Ceramic samples of (1−x)BiFeO3−xPbFe0.5Sb0.5O3(BFO–xPFS), (1−x)BiFeO3−xSrFe0.5Sb0.5O3(BFO–xSFS) where (x=0.05,0.1,…,0.9), (1−x)BiFeO3−xBaFe0.5Nb0.5O3 (BFO–xBFN) and (1−x)BiFeO3−xSrFe0.5Nb0.5O3 (BFO–xSFN) where (x=0,0.01,0.02,…,0.1,0.2,…,1) solid solutions with a perovskite structure were obtained. Mössbauer studies have shown that the Neel temperature TN concentration dependences of the systems studied are in good agreement with TN(x) calculated under the assumption of the ordered distribution of Fe3+ and nonmagnetic Sb5+ ions in the lattice. The TN values obtained for BFO–xBFN and BFO–xPFS are close to the values, calculated for cases of the disordered and ordered distribution of Fe3+ and nonmagnetic Nb5+ and Sb5+ ions in the lattice, respectively. The TN values of BFO–xSFN and BFO–xSFS are in the range between the calculated values for ordered and disordered cases. Moreover the anomaly on the TN(x) dependence for the BFO–xBFN and BFO–xSFN systems was found near x=0.7. This anomaly is most likely related to the destruction of the magnetic super exchange via the empty 6p state of Bi3+ ions.

The known multiferroics (MFs)-ternary oxides with perovskite-type structure PbB0,5′B0,5′′O3 that undergo successive phase transitions (PTs), ferroelectric (FE) or antiferroelectric (AFE) — at the Curie temperature, TC, and ferromagnetic (FM), antiferromagnetic (AFM) or ferrimagnetic at the Néel temperature, TN —and classical FEs and AFEs are considered. The dependences of the TC, TN on the interatomic bond A–O strains in their perovskite structures have been constructed. On constructed dependencies, some ternary MFs are discovered, which have comparatively high temperatures of first FE or AFE and second magnetic PTs but their difference TC–TN values are high comparatively with the binary MFs.

Constructed existence areas of different oxygen–octahedral structures of complex oxides are considered and compared. They are found on numerous facts of certain complex oxide compositions of three different structure types: successful and not-so-successful syntheses, on the one hand, and their interatomic bond characteristics calculation and analysis — on the other hand. Developed procedures of the crystal structure detailing the theoretical definition for every oxygen–octahedral structure and its constructing existence areas are shown. By using every structure existence area, one may predict the possibility of the specified complex oxides crystallization in the corresponding structure type.

Pure and superstoichiometric modified by 2wt.% Bi2O3 and 2wt.% manganese oxide (Mn2O3) ceramic samples of the binary system 0.71BiFeO3-0.29BaTiO3 were fabricated using conventional ceramic technology by double solid-phase synthesis with following sintering. Mechanical activation of synthesized powders was carried out at the stage of manufacturing press powders prepared for sintering. X-ray analysis at room temperature showed that all studied ceramics have pseudo-cubic symmetry. Grain morphology, dielectric and piezoelectric properties of selected solid solutions were investigated. The modification increased the homogeneity of the material, dielectric constant and piezomodulus d33 and also resulted in a decrease in the dielectric loss tangent. The highest piezoelectric coefficient d33=105 pC/N was obtained. Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior and region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 740–770K.

This paper demonstrates the influence of deposition parameters (temperature, power and time) and stoichiometric composition of thin aluminum nitride (AlN) coatings, the thickness of which varied from 320 to 1100nm deposited by DC reactive magnetron sputtering on their microstructure, mechanical and microtribological properties. The investigation revealed that high-deposition power (150W) and temperature (200∘C) lead to sputtering of coatings with high roughness, low mechanical and high microtribological properties. Such a phenomenon occurred due to the formation of a coarse-grained structure, high porosity and dendritic growth of the coating, which was observed on their cross-sections. Reducing the deposition temperature to 20∘C and power to 80–100W allowed to obtain a fine-crystalline structure demonstrating low-roughness values with crystallites evenly and compactly distributed over the surface. Such coatings showed higher mechanical and low microtribological properties. Surface resistivity was lower on coatings with a fine crystalline structure and correlated with the nitrogen content of the coating. In the course of the research, it was demonstrated that the optimal combination of microstructure, mechanical, microtribological properties and electrical resistivity for practical use in micro- and nanosensory applications may be achieved for the AlN coating with the thickness of 320nm and 29.71at.% N, deposited at 20∘C, 100W and 20min. Such a coating possesses the highest values of mechanical properties, low roughness and specific surface resistance, as well as low coefficient of friction and specific volumetric wear compared to all coatings under study.

The paper presents the results of experimental studies of synaptic plasticity in a memristive memory element based on nanocrystalline ZnO films grown by pulsed laser deposition. The obtained results can be used in the development of technological bases for the formation of high-performance multi-level artificial synapses for elements of neuroelectronics and hardware neural networks.

This paper studies the relaxation processes and electromechanical hysteresis in relaxor piezoceramics based on the PZT system. Measurements and analysis of the electric displacement and mechanical strain hysteresis loops recorded in bipolar AC electric fields in the frequency range 0.001–5Hz were performed by means of the electromechanical response characterization system (STEPHV) and program (STEP). It was found that the coercive field, remnant and saturation electric displacement, area of hysteresis loops and relative mechanical strain values are strongly dependent on frequency. As a result of this study, complete sets of parameters characterizing the switching and ferroelectric hysteresis processes in relaxor piezoceramics were obtained.

In this paper, we present the experimental results of the comprehensive study of the microstructural features and complex dielectric, elastic and electromechanical properties of the ferroelectrically “hard” piezoceramics based on the lead zirconate titanate (PZT) composition. For the measurements and analysis of the real and imaginary parts of the complex parameters of the studied piezoceramics as well as their frequency dependences, we used precision impedance analyzer Agilent 4294A and Piezoelectric Resonance Analysis Program (PRAP) software. We have found that the studied piezoceramics demonstrate a unique combination of dielectric, elastic and electromechanical parameters along with very low elastic and electromechanical losses and dispersion over a wide frequency range and can be used in various high-power ultrasonic applications.

A mathematical model of dynamic processes in a composite plate of prestressed piezoelectric (PE) and piezomagnetic (PM) layers is proposed. It is assumed that the initial strain state in the components of the plate is uniform and is induced by the action of initial mechanical stresses. In the quasi-static approximation, problems of shear horizontally polarized surface acoustic waves (SH-SAW) propagation in a PE/PM plate made of prestressed materials are considered. It is assumed that the materials of the plate layers in their natural state (NS) have symmetry class 6mm. The adhesion conditions are satisfied at the interface between the layers. The external surfaces of the heterostructure are in contact with the vacuum and are free from mechanical stress. Depending on the nature of the electrical and magnetic conditions specified on the external surfaces, four types of problems are considered. Using the example of a problem with electrically closed and magnetically open conditions on the external surfaces of a PZT-5H/CoFe2O4 plate, the features of the influence of the nature and magnitude of the initial mechanical effects on the velocities of SH waves are investigated. The possibility of changing the velocity characteristics of SAWs due to the initial mechanical effects is shown. The results are presented in dimensionless parameters and may be of significant interest for optimizing the structure of new materials in the development and design of devices and equipment operating on SH-SAW.

This paper discusses ways to search for lead-free functional materials for various applications. Using the example of the solid solution systems based on alkali metal niobates, the influence of the position on the phase diagram of the corresponding systems, the number of the components in them, and modification with mono- and combined metal oxides on their characteristics is shown. It has been established that the most effective in terms of piezoelectric characteristics are the solid solution systems in or near the morphotropic region, with 3 or 4 components. A number of materials have been developed to create highly sensitive electromechanical transducers, ultrasonic delay lines and other applications.

A model of a novel 1–3-type composite containing two ferroelectric components is put forward. In this composite, ferroelectric single crystal (SC) rods and ferroelectric ceramic rods are distributed in a polymer matrix. For a lead-free 1–1–3 composite based on domain-engineered [Lix(K1−yNay)1−x](Nb1−zTaz)O3:Mn SC, effective piezoelectric coefficients d3j∗ and g3j∗ and energy-harvesting figures of merit (FOMs) d3j∗g3j∗ are studied taking an active influence of the ferroelectric components into account. In a new m–mc diagram, regions of volume fractions of SC (m) and ceramic (mc) are determined where FOM d33∗g33∗ changes from 6⋅10−11 to 9⋅10−11 Pa−1. Effective parameters of the 1–1–3 and related 1–0–3 composites are compared, and consistency is shown. The large longitudinal piezoelectric coefficient g33∗ and FOM d33∗g33∗ of the lead-free 1–1–3 composite are to be of interest in piezoelectric sensorics and energy harvesting.

Polymer composites are emerging as critical materials for advanced dielectric energy storage due to their excellent flexibility, high dielectric constant (εr), and superior pressure resistance. They are ideal for next-generation devices requiring high power density and fast charge/discharge cycles. Strategic selection of fillers — optimizing their composition, structure, and surface properties within the polymer matrix — significantly enhances composite performance. This review examines recent advances in dielectric polymer composites, emphasizing the critical challenge of filler dispersion, which directly impacts homogeneity and overall performance. We categorize nanofillers based on size, shape, and material properties and discuss surface modification strategies to mitigate dielectric mismatches between fillers and matrices. We also explore the design of transition layers around nanofillers to improve filler-matrix interactions and enhance dielectric performance. Additionally, the spatial architecture of multilayer films is examined, demonstrating how layer arrangement optimizes electric field distribution and breakdown strength. Finally, we address critical challenges in developing high-performance dielectric polymer composites for capacitors and outline future research directions to improve recoverable energy density, stability, and scalability for commercial applications. This review offers valuable insights for researchers and engineers working to advance dielectric energy storage materials.

This work investigated the structure and dielectric behavior of precursor-derived spark plasma sintered (SPS) hafnium dioxide (HfO2). X-ray diffractograms confirmed the presence of monoclinic HfO2 (m-HfO2) and scanning electron micrographs revealed micron/nanosized grains and grain boundaries in SPS m-HfO2. The theoretical density of ceramics is 94%, and the porosity is very low. In the temperature interval of 25–200°C, the real part of the permittivity (ε′) is almost frequency- and temperature-independent and the ε′ value is about 21 in the frequency range 102?106Hz. ε′ of SPS ceramics is higher than that of traditionally sintered HfO2 ceramics. At temperatures above 225°C, there is a sharp increase in the permittivity and loss at low measuring frequencies. In order to comprehend the underlying conduction mechanisms, an analysis of the dispersion dependences of the dielectric response was undertaken. High permittivity values were attributed to the space charge polarization mechanism occurring at grain boundaries due to the thermally activated movement of oxygen vacancies. The DC conductivity of SPS m-HfO2 is thermally activated, and conductivity is determined by oxygen vacancies through hopping mechanism.

In this paper, we present the electric field controllable diffractive optical elements in strontium–barium niobate single crystals with stable tailored spiral-shaped domain structure and demonstrate the generation of optical beam with orbital angular momentum. The required domain pattern was created in the sample with initial domain structure by electric field application using the photolithographically defined liquid electrode. A series of bipolar triangular electric field pulses were applied to the sample for determination of the optimal parameters for complete polarization switching under the electrode. The stable tailored domain pattern of the spiral shape was created by the application of the unipolar pulse of a special shape. The complete switching under the electrode and partial switching under the photoresist layer have been revealed. The imaging by Cherenkov-type second harmonic generation microscopy confirmed that the created domain structure reaches the opposite polar surface. The imaging of the diffraction pattern of the laser beam passing through a voltage-biased DOE confirmed the formation of the beam with orbital angular momentum. The half-wave voltages of 237V and 302V for wavelength 632.8nm and 532nm, respectively, for 2-mm-thick sample were measured. The obtained knowledge can be used for the development of domain engineering methods in strontium–barium niobate single crystals for the creation of tailored domain structures for manufacturing of electric field controllable diffractive optical elements.

The primary aim of the current research is to explore the impact of yttrium-doping in barium stannate titanate (Ba1?1.5xYxTi1?zSnzO3) to investigate the variation in its structural and electrical properties. The specimens were synthesized using a solid-state method, wherein the precursors were heated together until they reacted to form the desired compounds. Subsequently, X-ray diffractometric analysis was employed to confirm the crystallographic phases. Archimedes’ method was used to determine the density of the material. An Electron Paramagnetic Resonance (EPR) study was conducted to examine the nature of defect centers and impurity ions within the synthesized ceramics. Furthermore, the impact of yttrium (Y) substitution on the system’s morphology and grain growth was evaluated through SEM micrographs. Selective compositions were found with enhanced dielectric properties of barium titanate ceramic, exhibiting a dielectric constant of 9816 at the transition point. The highest value among all studied samples had a clear indication of DC conductivity. Piezoelectric coefficient (d33) and P-E hysteresis loops were also investigated for these samples, indicating potential applications in electronic devices for the modified material’s improved ferroelectric properties.

By X-ray diffraction and dielectric spectroscopy, the crystal structure, phase composition, and properties of Sr0.6Ba0.4Nb2O6/Ba2NdFeNb4O15/Sr0.6Ba0.4Nb2O6/Ba2NdFeNb4O15/SrRuO3/MgO and Ba2NdFeNb4O15/Sr0.6Ba0.4Nb2O6/Ba2NdFeNb4O15/Sr0.6Ba0.4Nb2O6/SrRuO3/MgO multilayer heterostructures were studied. The heterostructures were manufactured under identical conditions but differing in the layer deposition sequence. It is shown that the orientation domains are formed in each Ba2NdFeNb4O15 (BNFN) and Sr0.6Ba0.4Nb2O6 (SBN) layers. BNFN and SBN layers have tetragonal unit cells with tensile out-of-plane strain and compression in-plane strain. At T=?100…100°C both heterostructures are characterized by fairly high relative permittivity values. The reasons for the revealed regularities are discussed.

Solid solutions (SS) with a quasi-binary cross-section of a four-component system of the composition (1?x)(Na0.5K0.5)NbO3–xPb(Ti0.5Zr0.5)O3, based on compositions with fundamentally different physical responses (Na, K)NbO3 (KNN), Pb(Ti, Zr)O3 (PZT), have been prepared by a two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. The influence of thermal cycling on the dielectric properties of ceramic SS with x=0.00,…,1.00 has been studied. It has been shown that thermally induced fatigue does not have a significant effect on the Curie temperature and the diffusing of the phase transition (PT) of SS containing only extreme components. It has been found that when the concentration of PZT in the studied system is varied, the ε′/ε0(T) dependencies take on a form characteristic of ferroelectrics with a diffuse PT. When the repolarisation cycles are varied, the diffusing parameter and the Curie and Burns temperatures show a wave-like behavior. The observed effects are explained by the interaction of different defect types. A conclusion is drawn on the possible practical applications of the studied SS.

Rare earth-doped ferroelectric (FE) ceramics have attracted much attention due to their great potential application for novel multifunctional optical-electro devices. This study successfully devised and fabricated tungsten bronze Sr2?xSmxAg0.2 Na0.8Nb5?xZrxO15 ceramics, demonstrating exceptional energy storage and luminescent properties suitable for multifunctional capacitors. Effects of co-doping Sm3+ and Zr4+ in A and B sites on the phases structure, FE, energy storage and photoluminescence properties of Sr2?xSmxAg0.2Na0.8Nb5?xZrxO15 ceramics were systematically investigated. Through employing various collaborative optimization strategies, encompassing the refinement of ceramic grains, the induction of nanodomain generation and the incorporation of large bandgap components, enhancement of breakdown strength and regulation of constructing relaxor FEs were achieved. Encouragingly, the high-performance multifunctional materials with remarkable recoverable energy storage metrics (Wrec～ 3.72J/cm3, η～ 82.7%), brilliant red-orange light emission and distinguished frequency and temperature stabilities within specific ranges were obtained in Sr1.7Sm0.3Ag0.2Na0.8Nb4.7Zr0.3O15 ceramics. Besides, the multifunctional ceramics demonstrated a high-power density (68.1MW/cm3), a substantial current density (908.1A/cm2) and a fast discharge time (51ns) at 190kV/cm. These findings suggest that the designed Sr2?xSmxAg0.2Na0.8Nb5?xZrxO15 ceramics hold promise as candidate materials for dielectric capacitors.

We conducted a study on Mn doping in 67Pb (Mg1∕3Nb2∕3)O3-33PbTiO3(67PMN-33PT), which is a ferroelectric material exhibiting a morphotropic phase boundary (MPB). The samples were doped with MnO2 at mass ratios ranging from 0.5 to 5.0wt.% and subsequently sintered at temperatures ranging from 1200 to 1260°C. Experimental analysis of electrical properties was performed within the temperature range of ?80–200°C. Electron paramagnetic resonance (EPR) testing was conducted on these samples to investigate Mn solubility in PMN-PT ceramics and their existence in different valence states. The results indicate that at a doping ratio of 0.5wt.% and sintering temperature of 1220–1240°C, Mn ions achieved a homogeneous dispersion within the crystal lattice, leading to the enhanced electromechanical Qm factor (510) and the reduced dielectric loss tan δ to minimum (0.30%) compared to the no doping Mn, however, as the Mn ions dopant content increase higher than 1.0wt.% and sintering temperatures 1200–1260°, the unexpected results have been observed that both Qm and tan δ are enhanced to about 1200, 0.87 up to 1.5wt.% MnO2, and then, Qm decreases to 510, but tan δ increases to 3.78% for 5 wt.% MnO2. The machinal Qm and dielectric loss can be understood by the (Mn-Vo) defect dipoles in lattice, domain wall and grain-bounary, together with the increasing of the MnO2, Mn2O3 or their mixed phase of Mn3O4 in the grain boundary.

With the rapid development of electronic integration technology, highly integrated chips are in urgent need of packaging materials that are thermally matched to printed circuit boards. Here, Zn1?xCoxAl2O4 (ZCAO, x= 0.00–0.20) ceramics are synthesized using the solid-state reaction method. The phase composition, microstructure, microwave dielectric properties and CTE of Zn2+ in the ZnAl2O4 ceramic substituted by Co2+ are systematically revealed. An appropriate amount of Co2+ substitution promotes a more homogeneous grain growth to form a dense microstructure. The average grain size, bulk density and relative density of ZCAO (x=0.10) ceramic are 1.59μm, 4.472g/cm3 and 97.4%, respectively. The optimal microwave dielectric properties (εr=8.2, Q×f=100,701GHz, τf=?66ppm/°C) of the ZCAO (x=0.10) ceramic sintered at 1450°C are achieved. More importantly, the ZCAO (x = 0.10) possesses a CTE = 11.59ppm/°C that is nearly thermally matched to the printed circuit boards (PCB, CTEPCB = 12ppm/°C). This ceramic has great potential for application in the electronic packaging of PCB devices.

The A-site rare earth-doped Bi4Ti3O12 (BTO) has been highly interested in nonvolatile ferroelectric random memory devices, piezoelectric devices, electro-optical devices, capacitors, sensors, transducers, etc., due to its low coercive field and superior fatigue resistance properties. However, single B-site doping has not received corresponding attention. In this work, BTO and Bi4Ti3.9Sn0.1O12 (BTS) thin films were prepared by sol–gel method, in which the doping of Sn effectively restrained the grain growth and decreased the grain size, as well as diminished the formation of oxygen vacancies and enhanced the breakdown field. This leads to a significant enhancement of the ferroelectric properties of the BTO films. The final BTS films exhibit excellent saturation P–E loops with a remnant polarization (2Pr) of 94.4μC/cm2 and a coercive field (2Ec) of 0.69MV/cm at a maximum electric field of 2.8MV/cm. The ferroelectric fatigue and dielectric properties of BTS film were also characterized. The results suggest that doping of Sn at B-site can effectively improve the breakdown strength and enhance the ferroelectric properties of the BTO film.

Ternary piezoelectric ceramics Pb(In1∕2Nb1∕2)O3–Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PIN–PMN–PT) exhibit excellent temperature stability and hold great potential for high-frequency and high-power applications. However, its piezoelectric performance is much lower than that of the famous binary Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PMN–PT) system. In this work, high-performance 15PIN–50PMN–35PT piezoceramics with piezoelectric coefficient d33 of 700 pC/N, electromechanical coupling coefficient kp of 66% and high Curie temperature TC of 199°C were fabricated. Effect of Samarium (Sm) doping content on the ferroelectric, dielectric, electromechanical and piezoelectric properties and structures of 15PIN–50PMN–35PT piezoelectric ceramics were investigated, and results reveal that increasing the amount of Sm doping leads to a significant decrease of d33, kp, TC and other properties. This phenomenon is different from the previously reported results in Sm-doped binary PMN–PT ceramics. The room temperature and variable temperature phase structure and room temperature microstructure were studied to explain this phenomenon.

As a newly emerging catalysis, tribocatalysis is receiving more and more attention with regard to the criteria to fabricate or choose materials as catalysts for it. In this study, two different commercial silicon (Si) powders, Si30 and Si300, were adopted as catalysts in tribocatalytic degradation of organic dyes. Only round nanoparticles from 30 to 100nm were observed in Si30, while some highly large and irregular particles, as large as 1000nm × 500nm and with a roughly flat major surface, could be observed in Si300. Stimulated through magnetic stirring using Teflon magnetic rotary disks, as much as 95% of 20 mg/L rhodamine B (RhB) solution and 97% of 20 mg/L methyl orange (MO) solution were degraded by Si300 after 3h and 50min, respectively; while only 73% of RhB and 83% of MO were degraded by Si30 after 5h and 4h, respectively. EPR spectra showed that more superoxide and hydroxyl radicals were generated by Si300 under magnetic stirring. It is proposed that in those large particles in Si300, their large flat major surfaces dramatically enhance their absorption of mechanical energy through friction and there are much less lattice defects to hinder electrons and holes from diffusing to the surface, which both results in the contrasting tribocatalytic degradations of organic dyes between Si300 and Si30. These findings reveal a huge difference in tribocatalytic performance among different materials of the same composition.

Electrocaloric (EC) refrigeration, which employs ferroelectric (FE) ceramics as a working medium, is regarded as a promising green refrigeration technology that could potentially replace vapor-compression refrigeration. One of the principal considerations in EC application is the capacity to attain high EC strength near room temperature. In this work, we investigated the EC effect in Sm/Mn co-doped BaTiO3 [(Ba1?1.5xSmx)(Ti0.99Mn0.01)O3] ceramics. As the smallest trivalent ion that can totally occupy the A site, Sm3+ is not only capable of shifting the Curie temperature but also of optimizing the EC effect. Furthermore, the introduction of the Mn element into the matrix results in the formation of defect dipoles, which also serves to enhance the EC performance. Therefore, large EC strengths of ΔT∕ΔE=0.49KmmkV?1 (@51°C), 0.34KmmkV?1 (@39°C) and 0.21KmmkV?1 (@30°C) were, respectively, achieved in x=0.05–0.07 ceramics, demonstrating the potential for future refrigeration applications.

Rare-earth elements Sm3+-, Pr3+-, Ho3+- and Er3+-doped (K0.5Na0.5)0.974La0.025Nb0.975Bi0.025O3 ceramics (abbreviated as KNLNB-0.1%RE) were prepared by conventional solid-phase sintering method. The structure, transparency, energy storage and photoluminescence properties of the samples are investigated. All ceramics have the pseudo-cubic phase structure without the impurity phase at room temperature. KNLNB-0.1%RE ceramics exhibit excellent optical transmittance, with KNLNB-0.1%Ho achieving 71.8% transmittance in the visible wavelength range (780nm) and largest effective energy storage density of 1.45J/cm3. In our experiments, rare-earth-doped KNLNB ceramics exhibit photoluminescence effects. This work facilitates the development of transparent energy storage ceramics with fluorescent effects.

In this work, a series of BiFeO3/ZnO composites with varying molar ratio of BiFeO3 to ZnO (Bi:Zn = 2.5:1, 5:1, 10:1, 20:1) have been synthesized via a one-step hydrothermal method and evaluated for their efficiency in rhodamine B (RhB) degradation performance. The morphology results reveal that the microsphere-shaped ZnO is dispersed on the surface of the blocky-like BiFeO3, with intimate contact between the two phases. It has been found that the maximum piezocatalytic activity could be achieved at BiFeO3/ZnO molar ratio of 5:1, with a degradation rate up to 92% for RhB. Compared with pure BiFeO3 and ZnO, the composites have superior piezocatalytic degradation performance. The reason for the enhanced piezocatalytic dye degradation rate may be that the BiFeO3/ZnO composites effectively separate the positive and negative charges to reduce the recombination of positive and negative charges. These active species, such as superoxide radicals (O2??) in the process of piezocatalytic, are proved on the active species capture experiments. The BiFeO3/ZnO composites have good piezocatalytic degradation performance, which provides an option for collecting vibration energy to degradation dye wastewater in the future.

Dielectrics with high permittivity and temperature stability are important for the development of high-temperature multilayer ceramic capacitors (MLCCs). In this study, Ca1?xNaxTi1?xNbxSiO5 (abbreviated as CTS?xNN) ceramics were prepared by solid-phase reaction method. The introduction of NN weakens the long-range ordered displacement of Ti, leading to a significant increase in the dielectric temperature stability. The CTS?2%NN samples exhibit high permittivity (53) and TCC ≤±170 ppm/°C in the range of ?55°C to 300°C. The CTS-based ceramics behave high dielectric temperature stability. In addition, the bandgap of the CTS-based ceramics increased significantly, which is favorable for improving the breakdown strength of the material. For x=4% samples, the breakdown strength reaches 621kV/cm. Thus, the designed CTS-based dielectrics are promising for high-temperature capacitors.

In this paper, silver (Ag) nanoparticle-modified zinc oxide (ZnO) nanowall photoconductive ultraviolet photodetector was prepared by using magnetron sputtering technology, electron beam evaporation method and hydrothermal method. The results showed that ZnO nanowalls exhibited a hexagonal wurtzite structure. ZnO nanowalls grew uniformly perpendicular to the substrate, and metallic Ag nanoparticles were uniformly attached to the surface of ZnO nanowalls, effectively improving the ZnO nanowall absorption capability in the ultraviolet light region. The dark current of the Ag-modified ZnO nanowall UV detector deposited by sputtering for 40s was 0.042mA, revealing a decrease of 44%. Under the irradiation of ultraviolet light with a wavelength of 325nm, the photocurrent reached 3.088mA, which increased by four times. The responsivity increased from 27.29 to 101.07mA/W, and the sensitivity increased from 8.07 to 73.52. In addition to the good repeatability and stability, the response time was reduced by 64%, and the recovery time was decreased by 50%.

Electronic and dielectric properties are essential for understanding many functional materials, predicting their behavior and optimizing their performance across different shapes, geometries and scales. Several approaches were developed and explored to investigate more or less deeply the appropriate properties. One of the most appealing, accurate and efficient approach is first principle simulations based on modern theory of polarization. Especially with the increased availability of powerful computational resources and techniques. Building upon these advancements, our contribution aims to elucidate an efficient methodology for studying electronic and dielectric properties by applying the Berry phase and Maximally Localized Wannier functions methods. Our exploration will initially focus on a systematic study of the electronic, chemical bonding, ferroelectric and piezoelectric properties of the well-known prototypical bulk system PbTiO3. Subsequently, we will extend our study to examine slab properties as surface termination and slab thickness effect on electronic properties, utilizing the robust Wannier-justified Tight Binding model.

In this paper, based on the developed statistical-thermodynamic model, which is based on data on the local structure of the compound and taking into account the striction interaction caused by the large sizes of the Ba and K cations, the formation of ferroelectric phases in BaTiO3 and KNbO3 perovskites has been studied. Based on the modified eight-minimum model, it has been possible to qualitatively identify the factors that determine the features of the thermodynamic behavior of these crystals and to reproduce the process of formation of the whole set of phase states observed in BaTiO3 and KNbO3.

Yttrium oxide–magnesium oxide (Y2O3–MgO) composite nanopowders were synthesized via three distinct methods: sol–gel, co-precipitation and glycine–nitrate process. The synthesized powders were calcined at various temperatures, and their microstructure, specific surface area and particle size were characterized. A comparative study was conducted to assess the impact of the synthesis method on the microstructure and transparency of the resulting ceramic sintering. Notably, the powder synthesized by the sol–gel technique exhibited the highest specific surface area and superior light transmittance, reaching a maximum of 85.33% at a wavelength of 5.31μm.

This paper presents the results of an experimental study of the percolation behavior of the complex dielectric constant of ceramic matrix composites (CMC). Samples of piezoactive CMC were obtained by joint sintering of synthesized PZT piezoceramic powder (matrix) and crushed particles of sintered PZT piezoceramics (filler) of different compositions. The experimental dependencies of real and imaginary parts of the complex dielectric constant of CMC on the porosity of piezoceramic matrix and volume content of ceramic filler particles were measured and analyzed. It was shown that the additional porosity of the ceramic matrix resulting from sintering of the CMC masks the dielectric percolation transition, that actually occurs at the volume concentration of ceramic filler close to percolation threshold (V ～ 1/3).

An analysis of heterophase states was carried out for ferro-active solid solutions of the system (1?x?y)NaNbO3?xKNbO3?yCdNb2O6. A complete stress relief at interfaces between phases in solid solutions with y=0.05 and x=0.10, 0.40, and 0.45 is realized at the single-domain state of the tetragonal and orthorhombic phases. In solid solutions with y=0.05 and x=0.05 and 0.20, as well as with y=0.075 and 0.10, and x=0.15, the formation of a planar interphase boundary being parallel to a zero-net-strain plane occurs at the elastic matching of the single-domain tetragonal and polydomain orthorhombic phases. In contrast to this, at y=0.05 and x=0.25, 0.30, and 0.35, the complete stress relief is associated with a co-existence of the single-domain orthorhombic and polydomain tetragonal phases, however in some cases, the tetragonal phase aims at a monodomainization.

In this paper, we present the study of the shape change on the polar surface and in the bulk of the walls of lamellar domains as a result of local switching by focused ion beam. Periodical lamellar domain structures (PDS) are created alternatively by two methods: (i) electric-field poling using photolithographically defined electrodes and (ii) ion beam poling. The dot irradiation of Z+ areas near the walls of lamellar domains leads to the formation of faceted or rounded hexagonal domains. For e-field PDS additional formation of nanodomain ensembles was observed. We have revealed two types of domain wall shape changes induced by irradiation: (1) merging of the hexagonal domain with the domain wall for Z+ areas; (2) formation of rounded distortion of the domain wall for Z? areas. For Z+ areas irradiation, the domain wall distortion was described by a simple model of independent growth of isolated domain with its subsequent merging with a static domain wall. For Z? surface irradiation, the domain wall shift increases linearly with the distance between the irradiation dot and the wall. It was revealed that the merging between the growing hexagonal pyramid domain and lamellar domain can be obtained in the bulk even for absence of merging at the surface. All obtained results have been explained within a kinetic approach to the domain wall motion by step generation. The switching field consists of inputs produced by: (i) the charges injected during dot irradiation into the photoresist layer and crystal bulk, (ii) the charges injected during the creation of i-beam PDS, (iii) the depolarization fields. The transition of the shapes of isolated domains and wall distortions from faceted to rounded ones with field increase was attributed to the transition from determined step generation to stochastic one.

0.7Bi(1?x)NdxFeO3–0.3BaTiO3 (BNFO–BTO, x=0.005, 0.010, 0.020 and 0.050) ceramics were fabricated using the high-temperature solid-state reaction method. The X-ray diffraction (XRD) patterns revealed that the primary phase in these ceramics was pseudocubic. The Scanning Electron Microscopy (SEM) micrographs exhibited dense microstructures throughout all BNFO–BTO ceramics. Furthermore, the temperature dependence of dielectric behaviors and ferroelectric hysteresis loop shapes suggested the occurrence of a relaxor ferroelectric-type phase transition in BNFO–BTO ceramics. Additionally, the frequency dispersion characteristics and remnant polarization were enhanced with increasing substitution of Bi3+ by Nd3+. Conducted impedance analysis on 0.7Bi(1?x)NdxFeO3–0.3BaTiO3 ceramics and two dielectric responses of the grain at high frequency and grain boundary at low frequency were illustrated, respectively. The combination of imaginary impedance (Z″) and imaginary modulus (M″) versus logf plots revealed that the charge carriers’ motion was not entirely long-range, short-range migration also exists. Through calculations based on Curie–Weiss Law, the relaxation activation energy (Ea) and conductance activation energy (Ec) were investigated, confirming that doping Nd3+ effectively mitigates the concentration of oxygen vacancies (OVs) and prevents the formation of oxygen vacancies clusters, ultimately suppressing conductivity in BNFO–BTO ceramics.

Dielectric relaxation behaviors of (1–x)BaTiO3–xBi(Zn1∕2Zr1∕2)O3 (BT–BZZ, 0.04≤x≤0.20) have been analyzed at various temperatures. Both Havriliak–Negami (H–N) and Jurlewicz–Weron–Stanislavsky (J–W–S) relaxations are identified in these ceramic compositions. H–N relaxation happens in compositions with a small mole ratio of Bi(Zn1∕2Zr1∕2)O3 (BZZ), while J–W–S type relaxation appears in compositions with a large mole ratio. Static dielectric constant, relaxation time and Jonscher indices are also obtained. The general trend of static dielectric constants decreases with increasing mole ratio of BZZ, while the relaxation time increases dramatically correspondingly. The low Jonscher index m is about 0.45 at low temperature for compositions with high mole ratio and increases with increasing of temperature. The high Jonscher index 1–n is around 0.1 at low temperature for compositions with high mole ratio and slightly decreases with increasing of temperature. Jonscher indices diagram with compositions of different mole ratios is plotted for easy identification of the relaxation types. Our results indicate that the relaxation behaviors in this BT–BZZ system show a strong deviation from the standard Debye model.

The Curie point of barium titanate (BaTiO3) has been a focal point of research since the discovery of its ferroelectric properties. Exploring methods to elevate the Curie point without relying on Pb as a dopant presents fresh opportunities for lead-free dielectric and/or piezoelectric materials. It is essential to avoid introducing ions like K+ and Na+, which could jeopardize the functional ceramic characteristics. This study delves into the stoichiometry of barium titanate, examining how impurities, point defects and doping techniques influence its Curie point, focus on the potential of doping and processing to enhance this property. BaTiO3 nanopowders were synthesized directly with varying Ba:Ti ratios in an ethanol–water solution at 60°C, followed by sintering at 1280°C and characterization through dielectric spectroscopy. A comparison was made with samples doped with Si, vapor-doped with Bi and vapor-doped with Pb. Results revealed that even minimal Si doping could boost the ferroelectric properties and elevate the Curie point, while vapor-doping with trace amounts of PbO or Bi2O3 significantly increased the Curie point, particularly in samples with higher Ti content. The impact of vapor dopants of PbO and Bi2O3 was similar, with a nominal doping level of 1mol% shifting the Curie point above 140°C. Notably, in samples with a Ba:Ti ratio of 0.95 vapor-doped with PbO, the Curie point rose to 146°C, a notable increase of 16°C, surpassing the traditional doping efficiency. This study offers fresh insights into enhancing the Curie point of barium titanate-based materials, exploring the intricate connections among chemical stoichiometry, dopants, point defects and dielectric properties. It highlights the significant influence of chemical composition, impurities, defects and doping strategies on the dielectric characteristics of barium titanate.

X-ray diffraction and dielectric studies were performed on synthesized ceramic samples of the section (1–x) (0.8PbMg1∕3Nb2∕3O3?0.2BiScO3)? x(0.8PbTiO3?0.2BiScO3) with x=0–1 of the ternary BiScO3–PbTiO3–PbMg1∕3Nb2∕3O3 (BS–PT–PMN) system, including the temperature dependence of thermally stimulated depolarization currents (TSDC). It was found that the samples are solid solutions with a perovskite structure, which have cubic symmetry in the range of x = 0–0.587 and tetragonal symmetry in the range of x = 0.680–1. In the intermediate composition range of x = 0.587–0.680 (morphotropic region — MR), the samples consist of a mixture of solid solutions of different symmetries. Data on the change in dielectric properties and TSDC(T) dependencies of solid solutions with a change in their composition were obtained. It was found that samples of compositions x =0–0.625 and 0.6875–1 exhibit relaxor-ferroelectric and conventional ferroelectric properties, respectively, while samples of compositions x = 0.625–0.6875 combine ferroelectric and relaxor-ferroelectric properties.

Via the method of cold sintering with post-annealing, the lead-free ceramics K0.45Na0.45Li0.1NbO3 were prepared. The cold sintered pellet without post-annealing shows a relative density (ρr) of 77.9%, which is larger than ρr of the green pellet via the conventional solid-state sintering (SSS) method (～65.1%). The cold sintered pellets were post-annealed at temperatures between 975°C and 1075°C. The effect of post-annealing temperatures on microstructure, dielectric, ferroelectric and piezoelectric properties of the ceramics was studied in detail. After being post-annealed, the relative densities and grain sizes of the ceramics were increased. The ceramics post-annealed at 1050°C show excellent dielectric, ferroelectric and piezoelectric properties. Compared to the conventional SSS method, the method of cold sintering with post-annealing is successful in preparing dense K0.45Na0.45Li0.1NbO3 lead-free ceramics in a wide temperature range and at relatively low temperatures.

An n-type channel transparent thin film field-effect transistor (FET) using a top-gate configuration on a sapphire substrate is presented. ZnO:Li film was used as a channel, and MgF2 film as a gate insulator. Measurements showed that ZnO:Li films are ferroelectrics with spontaneous polarization PS=1–5μC/cm2 and coercive field EC=5–10kV/cm. The dependences of drain–source current on drain–source voltage at various gate–source voltages in two antiparallel PS states were measured and the values of field-effect mobility and threshold voltage were determined for two PS states are as follows: (a) μ=1.5cm2/Vs, Uth=30V; (b) μ=1.7cm2/Vs, Uth=23V. Thus, PS switching leads to a change in FET channel parameters. Results can be used to create a bistable or, more precisely, digital FET.

Orientation anisotropy is a well-known essential character for polarization characteristics of ferroelectric materials, which has been widely investigated in conventional ferroelectric random access memories. In this work, we study the effects of orientation on the tunneling electroresistance (TER) of ferroelectric tunnel junctions (FTJs). Rhombohedral Pb(Zr0.7,Ti0.3)O3 (PZT) that has the polar axis along the ?111? orientation is adopted as potential barriers and two kinds of FTJs that are composed of (001)- and (111)-oriented PZT barriers and Nb:SrTiO3 (Nb:STO) electrodes, respectively, are fabricated. The (111)-oriented Pt/PZT/Nb:STO FTJ exhibits a giant ON/OFF ratio of ～1.9×105, about 30 times that of the (001)-oriented device, due to the lowered PZT barrier in the ON state and the widen Schottky barrier in the OFF state based on current and capacitance analyses. In addition, compared to the (001)-oriented device, the (111)-oriented FTJ shows a sharper and faster switching between the ON and OFF states according to the nucleation-limited-switching dynamics model, giving rise to good linearity in memristive behaviors for synaptic plasticity and reliable retention and endurance properties for the resistance switching. The improved TER properties are ascribed to larger effective polarizations and 180° switching in the (111)-oriented PZT barrier. These results facilitate the design and fabrication of high-performance FTJ devices with the optimization of crystallographic orientation and polarization switching characteristics.

Two 0.93(Na0.5Bi0.5)TiO3–0.07BaTiO3 ceramics were sintered for 2h and 3 h, respectively, by a conventional solid reaction method. The ceramic sintered for 2h showed a normal ferroelectric hysteresis loop and paramagnetic behavior, while the ceramic sintered for 3h showed a pinched ferroelectric hysteresis loop, weak ferromagnetism, and enhanced magnetoelectric coupling. The origins of the sintering time-related multiferroic properties are discussed in detail. The work offers a new way to induce multiferroicity in ceramics by tuning sintering time.

Piezocatalysis has emerged as a promising environmental remediation technique, and the exploration of environmentally friendly and high-performance piezocatalysts is crucial for their practical applications. In this work, the bismuth sodium titanate (Na0.5Bi0.5TiO3 (NBT)) exhibited efficient piezocatalytic activity toward typical organic pollutants degradation, including acid orange 7, methylene blue, rhodamine B and methyl orange. Notably, rhodamine B was degraded by 98.1% within 30min with a reaction rate constant of 0.130min?1. Furthermore, the NBT achieved a hydrogen peroxide production efficiency of 538μmol/g?h without the sacrificial agent, indicating that the NBT is a superior piezocatalyst for dye degradation and hydrogen peroxide generation. This work demonstrated that by using mechanical energy, the NBT can be used for degrading organic pollutants in wastewater and hydrogen peroxide generation.

N-doped titanium dioxide (TiO2) hollow nanospheres with abundant oxygen vacancies were successfully synthesized by coupling urea treatment and annealing in an N2 atmosphere. The pristine TiO2 hollow nanospheres exhibit a shallow donor level for electron trapping, while the urea treatment generates a N 2p acceptor level for hole trapping. After annealing in N2, the sufficient N atoms generate abundant oxygen vacancies for trapping electrons, resulting in further improved charge separation efficiency. The N-doped TiO2 exhibits the highest H2 evolution rate, reaching 2867μmolg?1h?1, which is six times higher than that of pristine TiO2 hollow nanospheres. The introduction of oxygen vacancies by interstitial N provides a promising way to improve the photocatalysis activity of photocatalysts.

In this work, dense CdCu3(Al1∕2Ta1∕2)xTi4?xO12 ceramics were prepared by a conventional solid phase method. The effect of Al3+/Ta5+ dopants on the dielectric properties of CdCu3Ti4O12 ceramics was systematically investigated. Upon Al3+/Ta5+ co-doping, the dielectric properties of CdCu3(Al1∕2Ta1∕2)xTi4?xO12 were significantly enhanced. Particularly, the CdCu3(Al1∕2Ta1∕2)0.05Ti3.95O12 material displays a decent dielectric property, where dielectric constants (εr～27181), loss tangent (tan δ～0.069) at a test frequency of 1kHz are able to satisfy the application temperature requirement of the Y6R capacitor. Surprisingly, the refined grains resulting from Al3+/Ta5+ co-doping lead to heightened resistance at grain boundaries, which is closely associated with enhanced dielectric properties. Meanwhile, the giant dielectric property of the materials can be attributed to the effect of the internal barrier layer capacitance. The obtained results are expected to provide a new idea for obtaining high dielectric constant and low loss tangent in CdCTO-based materials and promote the practical application of such materials.

Intrinsic SrTiO3 is a quantum paraelectric,but moderately Bi-doped SrTiO3 exhibits dielectric frequency dispersion similar to relaxor ferroelectrics. In this paper,detailed electron microscopic studies of the microstructures of Bi-doped SrTiO3 samples were presented. It was found that the Sr sites were replaced by off-central Bi,resulting in tensile strain in the strontium titanate (STO) lattice. In the Bi-doped SrTiO3 samples,the valence of titanium mainly showed the Ti4+ characteristic. According to the dielectric behavior and microstructure analysis,the polar nanoregions (PNRs) composed of strained SrTiO3 nanoclusters should be responsible for the ferroelectric relaxor behavior in samples with moderate Bi content.

The paper presents the results of a study of the microwave absorption properties of ceramic materials based on bismuth ferrite containing rare earth elements,as well as systems of solid solutions (1−x)BiFeO3–xPbFe1/2Nb1/2O3 in a wide range of component concentrations. The methodology for measuring and calculating the parameters of samples of the materials under study is described. The influence of structural and microstructural factors on the average and maximum level of microwave absorption of the materials under study in a wide frequency range is analyzed. A comparison of the microwave absorbing properties of these materials with industrial absorbers has been carried out,and prospects for application in microwave technology have been shown.

Ceramic samples of the (1−x)BaTiO3⋅xPbFe2/3W1/3O3,0≤x≤1 ((1−x)BT⋅xPFW) system were synthesized by solid-state reactions method. The samples were characterized by X-ray diffraction (XRD) and dielectric studies,as well as by the measurements of the thermally stimulated depolarization currents (TSDC). It was found that the predominant phase in the samples is presented by the (Ba1−xPbx)(Ti1−xFe2x/3Wx/3)O3 solid solutions with a perovskite structure,herewith the samples with 0≤x<0.25 are practically single-phase,and with 0.25≤x<1 contain the impurity phase BaWO4 (up to 15 mass.% at x=0.60–0.90). Information has been obtained about the changes in the structural and dielectric characteristics of the solid solutions with the change of their composition. It is established that the solid solutions crystal lattice symmetry at 296 K changes from tetragonal at x≤0.04 to cubic at x≥0.05. An increase in the PFW content in solid solutions causes a gradual change in their properties from ferroelectric at 0≤x<0.10 to relaxor ferroelectric at 0.10≤x≤0.25,and then to properties similar to those of the dipole glass with weak or zero correlation between dipoles at 0.25<x≲0.90. The addition of BT to PFW leads to rather quick degradation of the relaxor ferroelectric properties of PFW in the region x=0.9–1.0.

A high performance of novel three-component composites with 2–1–2 connectivity is reported and discussed. Layers of the composites are parallel-connected,and each layer contains the ferroelectric (FE) component. The layer of the first type (LFT) represents domain-engineered single crystal poled along either [0 0 1] or [0 1 1]. The layer of the second type is described as a system of long FE ceramic rods that have the shape of an elliptic cylinder and are aligned in a polymer medium. Piezoelectric coefficients d3j∗ and g3j∗ and sets of figures of merit (FOM) (energy-harvesting d3j∗g3j∗,modified F3j∗σ for a stress-driven harvester and modified F3j∗ξ for a strain-driven harvester) are analyzed to show their large values and specifics of the anisotropy when varying volume fractions of components and a rotation angle of the ceramic rod bases. For the first time,the studied parameters are compared in two directions: (i) the composite based on [0 0 1]-poled single crystal versus the composite based on [0 1 1]-poled single crystal and (ii) the lead-free composite versus the lead-containing composite (both based on [0 0 1]-poled single crystals). The advantages of the high-performance lead-free composite are discussed. The 2–1–2 composites put forward in this paper are of interest as advanced materials suitable for piezoelectric sensors,actuators and energy-harvesting systems operating at constant stress or strain.

The Mg2Al4Si5−xSnxO18 (0≤x≤0.20) ceramics were successfully synthesized via the solid-state reaction method. The XRD results show that the main phase of the ceramics is Mg2Al4Si5O18. When x=0,there is a second phase of Al2SiO5. With the increase of x,the content of Sn2+ gradually increased,the Al2SiO5 phase disappeared,and the SnO2 and MgAl2O4 phases appeared. In addition,the cell volume of the ceramic changes with the increase of x,which indicates that partial Sn2+ successfully enters the lattice with ion substitution and lattice distortion. The relative density and εr are highly correlated. The quality factor (Qf) is not only affected by the relative density but also by the symmetry of the [Si4Al2] ring. The bond strength as an evaluation of the stability of the crystal structure determines the magnitude of τf. Good microwave dielectric properties were achieved for samples at x=0.04 with sintering at 1400∘C: εr=4.86,Qf=17,000GHz and τf=−32ppm/∘C,demonstrating that Mg2Al4Si4.96Sn0.04O18 ceramics are an ideal candidate for microwave electronics.

New microwave dielectric ceramics of LiZnSbO4 were prepared by the reactive sintering method. Within the sintering temperature zone of 1350∘C–1385∘C,a single-phase LiZnSbO4 with an orthorhombic structure was identified by XRD refinement,which contains 10 molecular formula per unit cell (i.e.,Z=10). The relative density and average grain size had a main effect on εr and Q×f value of the LiZnSbO4 ceramics,whereas the phase assemblage was responsible for its τf. The 1375∘C-sintered LiZnSbO4 specimens owned comparable low εr∼6.5,but ultra-high Q×f∼74,500GHz (nearly three times) compared to LiZnPO4 and LiZnVO4 ultra-high Q×f∼74,500GHz (nearly three times) compared to LiZnPO4 and LiZnVO4 manufactured,which showed a return loss as low as 37.4dB,maximum gain of 5.7dB and a fractional bandwidth of 3.9% (11.95–12.43GHz).

In this work,solid-state reaction method and a two-step sintering procedure were successfully used to prepare neodymium-doped yttrium aluminum garnet (Nd:YAG) transparent dielectric ceramics. The effects of the microstructure and crystal structure of the ceramics on the microwave dielectric properties were investigated. Samples after vacuum sintered at 1600–1750∘C and further hot isostatic pressing (HIP) at 1700∘C had a pure YAG phase. The cell volume increased slightly after further HIP treatment compared to the vacuum-sintered ceramics. Combined with the disordered arrangement of the atoms in the HRTEM image,the lattice expansion could be explained by the entrance of larger ions into the YAG lattice. Moreover,the sintering drive provided by HIP could effectively eliminate the porosity in ceramics,increase the average grain size,and narrow the grain boundaries,which was conducive to the improvement of transmittance and quality factor (Qf) value. Finally,the sample that was vacuum sintered at 1700∘C and then exposed to HIP had outstanding microwave dielectric characteristics: εr=10.64,Qf=515,800GHz and τf=−21ppm/∘C.

Decreasing the scale of vanadium dioxide (VO2) structures is one of the ways to enhance the switching speed of the material. We study the properties of VO2 films of altered thicknesses in the range of 20–170nm prepared on c-sapphire substrates with a TiO2 sublayer by pulsed laser deposition (PLD) method. The synthesis regime to design a TiO2 film was preliminarily optimized based on XRD data. XRD patterns reveal an epitaxial growth of the VO2 films with distortion of the monoclinic cell to hexagonal symmetry. The positions of the lattice vibration modes in Raman spectra are similar to those in bulk VO2 when the film thickness is greater than ∼30nm. For VO2 films thicker that ∼20nm,a lattice strain results in the modes’ positions and intensity change. However,the electrically triggered transition in a ∼50nm thick VO2 film reveals forward and reverse switching times as short as 20ns and 400ns,correspondingly.

Two-dimensionality of the properties of a volumetric object may be defined by its anisotropy. Perovskite-like compounds of the family of Aurivillius–Smolensky phases (ASPs) have exactly this property. By studying perovskite-like compounds of the family of Aurivillius–Smolensky phases and the changes in the volume of the crystal lattice,occurring in them,namely the increase or decrease in the phase transition temperature (Curie temperature),the preferred direction of grain growth with an increase in the sintering temperature and,as a consequence,the increase in the relative permittivity,the main factor in all cases is the change in the linear parameters a and b,lying in the plane perpendicular to the c-axis.

As an important optical material,transparent polycrystalline alumina (PCA) ceramic is widely used in aerospace,high-temperature windows,medical due to its high strength,corrosion resistance,high hardness,and excellent stability at high temperatures. Since Al2O3 belongs to the crystal structure of the trigonal crystal system (a=b≠c),light is prone to birefringence when passing through the interior of the ceramic,and its transmittance is difficult to reach that of cubic crystal materials such as Y2O3 even under almost fully dense conditions. Using a special sintering process to decrease the sintering temperature and improve the real in-line transmittance of PCA ceramics has always been a research hotspot in related fields. In this work,a comprehensive review is made from the point of view of the sintering process based on the research status of transparent PCA ceramics in decades.

Low-temperature co-fired ceramics (LTCC) applied in millimeter/microwave and terahertz frequencies (5G/6G) have attracted a lot of attention recently. In this study, MgO-based dielectric ceramics were successfully sintered at 950°C with the sintering aids: x wt.% of LiF fluoride (x=2, 4, 6, 8, 10) and 0.5 wt.% of BBSZ (Bi2O3–B2O3–SiO2–ZnO) glass. BBSZ glass was introduced as another sintering aid to facilitate the sintering and densification. Crystalline structure and micro-morphology were investigated and analyzed. Dielectric properties (εr, Q×f, τf) at millimeter/microwave and terahertz wave frequencies were also studied. The ionic characteristics of Mg–O bond (fi), the lattice energy (U) and the bond energy (E) were calculated and analyzed. It is suggested that the optimal x=4, where εr=10.5, Q×f=120,000 GHz (@12 GHz) and τf=?26 ppm/°C at millimeter/microwave range. When the frequency was up to terahertz (1.0 THz), the εr values were 8.8–9.35 and the tanδ were 5.6×10?3–8.7×10?3. The experimental results indicated that the low-temperature sintered MgO-based ceramics have potential for millimeter/microwave and terahertz communication applications.

This paper presents the results of the first experimental observation of polarization reversal in the bulk of ferroelectric with a charged domain wall (CDW) under the action of an electric field on the example of a single crystal LiTaO3 plate. A CDW was obtained in the sample bulk at the locus of points with a sign change of the composition gradient which results from sample annealing in lithium rich atmosphere. Imaging of the domain structure in the bulk and its evolution on the surface made it possible to detect anomalous domain kinetics, which represents the growth of ledges on the CDW toward the polar surface. The main stages of the domain structure evolution on the polar surface, including the growth of isolated domains, as well as the formation and decay of the maze domain structure, were revealed. An analysis is made for the time dependence of the area fraction occupied by growing domains. We used a kinetic approach based on the analogy between the growth of domains and crystals to explain the obtained results.

Piezoelectric materials are commonly used in transducers to convert electromechanical signals due to their energy conversion characteristics. We designed a PIMNT/epoxy 2–2 composite to take full advantage of the excellent beam-mode piezoelectric and acoustic features of PIMNT single crystals. Following the approach used for piezoelectric ceramic composites, we selected PIMNT piezoelectric single crystal and EPO-TEK301-2 epoxy resin for the composite, and combined finite element analysis with experimental preparation. We prepared, tested and analyzed 2–2 piezoelectric single crystal composites with varying volume fractions, which showed high electromechanical coupling properties (kt>75%) and low acoustic impedance (Z<20 MRayl). These encouraging findings suggest the possibility of devising high-performance ultrasonic transducers utilizing the PIMNT/epoxy 2–2 composite.

In this paper, we studied the formation of self-organized domain arrays created by moving biased tip of scanning probe microscope (SPM) in deuterated TGS crystals. The shape of created domains depends significantly on scanning direction and applied voltage. For scanning along c axis, the domain shape drastically changed from arrays to stripe domains at 150 V. Scanning perpendicular to c axis led to formation of the array of the dashed domains. Increasing of the dashed domain length leads to change of domain shape from arrays of dashed domains to solid stripe domain. The obtained effect has been considered in terms of the kinetic approach as a result of formation of comb-like domain with charged domain walls in the bulk due to repetitive appearance of the domain spikes. The spontaneous backswitching under the action of the depolarization field leads to the fast growth of the tooth to the surface and results in the transformation of the domain shape. The computer simulation of the nonuniform motion of charged domain wall under the action of depolarization field has been done. The obtained results demonstrate the essential role of screening processes and pave the way for further improvement of domain engineering methods.

Graphene-oxide (GO) is one of the most commonly used carbon nanomaterials in advanced applications such as microwave absorption and EMI shielding, due to various advantages such as ease of synthesis and exfoliation, effective doping capability, and superior composite compatibility. In this study, we used the modified Hummer’s method to synthesize GO by exfoliating graphite powder, and a simple hydrothermal approach was employed for elemental doping and GO reduction. As nitrogen–sulfur (N, S) dual-doping precursors, thiourea and l-cysteine amino acids were utilized. The structural features and microporous network structure of GO aerogel foams were investigated. The microwave absorption capabilities of polyethersulfone-based nanocomposite films incorporating the as-produced nitrogen–sulfur enrich reduced GO (NS-rGO) are also explored. According to the physicochemical characterization, the existence of remarkable structural defects with a porous three-dimensional (3D) network was discovered due to heteroatom insertion and hydrothermal doping. Additionally, the dual-doped sample exhibited high Nitrogen and sulfur content of 8.93% and 13.19%, respectively. While NS-rGO possesses a higher conductivity of 174.7 μS compared to 12.65 μS for GO. The nanocomposites filled with NS-rGO foams demonstrated a high shielding efficiency (SE) of 45 dB in the X-band with a filler loading of 0.5 wt.%. This high SE arises from dopant heteroatoms and the heterogeneous interface, which induce interface polarization, thereby increasing microwave absorption and dielectric constant. It also results from multi-level reflections caused by the 3D porous structures. These findings offer valuable insights into the functionalization of carbon nanostructures and the development of 3D networks in GO-based functional materials, providing further guidance for engineering high-performance electromagnetic interference shielding materials.

This study focuses on the properties of Vanadium and Copper co-doped Barium Zirconate Titanate (BZT) for potential technological applications. Various doping ratios of CuO:V2O5 were used to synthesize the materials, and X-ray diffraction (XRD) confirmed a tetragonal phase in all samples. The grain density and dimensions decreased with higher concentrations of V2O5 and CuO. FTIR spectra confirmed the compositional structure and bonding of the samples. The impedance analysis indicated that higher doping concentrations facilitated charge conduction at grain boundaries. Dielectric relaxation was studied using the Havriliak–Negami model and electrical modulus behavior was analyzed. Activation energy values from Arrhenius fitting matched those from impedance data, suggesting the same type of charge carriers. The study revealed that elevated levels of V concentration induced charge carriers to exhibit hopping behavior, thereby enhancing conductivity. Conversely, higher Cu concentration impeded hopping, leading to a swift rise in activation energy.

Antimony sulfoiodide (SbSI) is a highly efficient energy conversion piezoelectric material. We obtained SbSI doped with tin (II) ions according to the formula Sb1-xSnxSI1-x (x=0.01–0.1). This heterovalent doping has been performed by the novel method of synthesis in an aqueous solution. The introduction of tin cations leads to a material Curie point increase of more than 10 K. The samples containing 5 mol.% of the dopant possess the best piezoelectric properties: piezomodule d33～750 pC/N, dielectric constant at a frequency of 1 kHz — 1758, dielectric loss tangent — 0.054, and piezosensitivity — 50 mV × m/N. Thus, tin-doped SbSI is a promising material for highly efficient electromechanical transducers and sensors.

Piezoelectric energy harvesting from mechanical vibrations has attracted considerable attention during the last decade. The homogeneous harvesters were studied experimentally or numerically by various models such as single degree of freedom (SDOF) modeling, finite element (FE) modeling as well as using analytical solutions. In this work, FE models for simulating a piezoelectric beam bimorph power harvester consisting of a laminated piezoelectric beam, a proof mass, and an electrical load (series or parallel connections) configurations are developed. The effects of the material and size of the substrate, the proof mass have been studied on the resonance frequencies and the output parameters of the piezoelectric generator (PEG). Numerical results obtained using the proposed procedure for piezoelectric bimorph power harvesters are in good agreement with the experimental data available in the literature. The proposed method can be used for modeling accurately this class of energy harvesting devices.

The integrable substrate for THz modulation directly influences both the quality of films and THz absorption. Currently, the available THz substrate candidate library is still not clear. Here, we have carried out a systematic investigation of commonly used commercial substrates, including Si, quartz SiO2, MgO, Al2O3, GdScO3 and TbScO3 in the range of 0.4–1.6 THz. It is found that low resistance Si, TSO and GSO are certainly not appropriate for THz light modulation due to their relatively higher absorption and dielectric constant, while the rest show better THz transmittance, low refractive index and loss. However, the dielectric constant and refractive index of high resistance Si are generally two times larger than quartz SiO2, Al2O3 and MgO. Compared with Al2O3 and MgO, quartz SiO2 shows at least 50% lower dielectric constant, refractive index and absorption, making it the best candidate. Our research is believed to build the rich substrate candidate library for THz range light modulation.

Statins are widely used in the treatment of hyperlipidemia disease, which are refractory in the municipal sewage treatment plant. The photocatalytic degradation of statins by the Z-scheme heterostructured photocatalyst is confirmed, but the degradation mechanism of statins needs to be further revealed. In this study, the effects of photocatalyst dosage, solution pH and humic acid (HA) on the photocatalysis of fluvastatin by ZnIn2S4/Bi2WO6 Z-scheme heterostructured photocatalyst (ZIS/BWO photocatalyst) were investigated and the degradation mechanism was proposed. Results showed that adsorption of fluvastatin was improved with the increase of photocatalyst dosage, but photoinduced desorption and light scattering resulted in the decrease of the removal of fluvastatin with high dosage. 0.2g/L of the ZIS/BWO photocatalyst was optimal dosage. 65.21% of fluvastatin was removed at pH=9, because high concentration of OH? was conducive to produce ?OH. The change of pH, competition of photons and active sites, and trapping of reactive oxygen species (ROS) by carboxyl group of HA combined to inhibit the photocatalysis of fluvastatin in the presence of HA. The C–C, C=C and C–N bonds of fluvastatin were attacked by a variety of ROS to generate degradable intermediates that were easily mineralized to H2O and CO2.

Calcium bismuth niobate (CBN) ceramic, as a core element of high-temperature piezoelectric sensors, has attracted widespread attention due to its high Curie temperature within the class of Aurivillius compounds. However, CBN usually faces two shortcomings: poor piezoelectric constant and low resistivity. In this work, CBN-based ceramics with donor–acceptor ions (W/Co) co-substituted at B-site were prepared by solid-state reaction method, and structure–property relationship of ceramics was studied in detail. Co-substitution of W/Co ions effectively improved the electrical property and hardness of CBN ceramics. CaBi2Nb1.91(W2/3Co1/3)0.09O9 exhibits enhanced electrical and mechanical properties including high resistivity of ～107Ω?cm at 500°C, piezoelectric constant of ～15.3 pC/N and hardness value of ～3.57GPa. These values are two orders of magnitude, over two times, and 1.36 times higher than those of pure CBN ceramic, respectively. This work provides a reference for exploring other bismuth-layered structural ceramics.

As a functional composite material, nickel-coated aluminum powder has been widely used in conductive fillers, electromagnetic shielding materials and other fields due to its advantages of low density, high conductivity and low cost. In this paper, nickel-plated aluminum powder was prepared by a sodium hypophosphite system. The effects of different nickel coating amounts (the percentage of nickel-plating quality to nickel-plated aluminum powder quality) on the morphology, phase, compaction resistivity and electromagnetic parameters of nickel-plated aluminum powder coating were studied. The X-Ray Diffraction (XRD) results proved the successful preparation of nickel-coated aluminum powders with different nickel coating amounts. The Scanning Electron Microscope (SEM) images clearly show the coating effect under different nickel coating amounts. By plating nickel on the surface of aluminum powder, the surface characteristics of aluminum powder are changed, so as to adjust its conductivity, resistance, stability and other properties, thus affecting its electromagnetic performance and wave absorption performance. The results show that the comprehensive absorbing performance is excellent when the nickel coating amount is 40%. The reflection loss of the sample with a thickness of 2.0mm is less than ?10dB in the frequency range of 10.17–12.38GHz. When the frequency is 10.72GHz, the minimum reflection loss reaches ?33.17dB.

Recently, high-performance lead zirconate titanate (Pb(Zr1?xTix)O3, PZT) ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range, better temperature stability, as well as larger piezoelectric properties and higher energy conversion efficiency. In this study, the perovskite-type ferroelectric ceramics with a chemical formula of Pb0.99?xGd0.01SrxZr0.53Ti0.47O3 (x=0 and 0.02, abbr. PGZT and PGSZT, respectively) were prepared by the traditional solid-state reaction route. The influences of Sr-doping on the phase structure, dielectric properties, ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated. The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10Hz and temperature range of 20–100°C. The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT, but also decreases its dielectric loss tangent, with the d33 value of 473pC/N, εr value of 1586 and tanδ value of 0.016 found in PGSZT. Also, PGSZT shows a high Curie temperature (TC) of 350°C. The underlying mechanisms of the property enhancement were identified as that the introduced Sr2+ replaces the volatile Pb2+ located at the A-site of the perovskite structure, thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics, consequently enhancing the dielectric and piezoelectric properties of PGZT. On the other hand, the frequency change in the low-frequency range (<1Hz) played a significant impact on the remanent polarization (Pr) and internal biased electric field (Ei) of PGSZT, but the frequency dependence of coercive field (Ec) tends to diminish in the high-frequency range (≥1Hz).

BiFeO3 (BFO), Mn-doped-BFO (BFMO), Ti-doped-BFO (BFTO), and (Mn,Ti)-codoped-BFO (BFMTO) thin films are fabricated on the Pt/TiO2/SiO2/Si substrates via a sol–gel method combined with spin-coating and the subsequent layer-by-layer annealing technique. Compared with BFO film, the BFMTO film exhibits the lowest leakage current density (～10?4A/cm2@290kV/cm). Notably, the polarization–electric field (P–E) loop of BFMTO film exhibits a positive displacement along the x-axis due to the existence of internal bias electric field, which is in agreement with the results of the PFM phase and amplitude curves. Especially, a very prominent inverse piezoelectric constant of d33～160pm/V was obtained, which overcomes other related thin films. The internal bias electric field of BFMTO film can be caused by the different work functions of the thin film and the bottom electrode, accumulation of oxygen vacancies and the formation of defect dipoles. Besides, the internal bias electric field of BFMTO film has a good stability at the same electric field after experiencing the test cycle from low electric field to high electric field (400–1900kV/cm). These results indicate that self-polarized BFMTO film can be integrated to devices without additional polarization process, and have a wide range of application in microelectromechanical systems.

In this work, a traditional solid-state method was adopted to prepare dense Ba0.85Ca0.15[(Zr0.1Ti0.9)1?x–(Nb0.5La0.5)x]O3(BCZT–xNL) lead-free relaxation ferroelectrics with excellent energy storage performance (ESP). Remarkably, a large breakdown field strength of BDS (～410kV/cm) resulting from decreased grain size by double ions doping at the B-site was achieved in BCZT–xNL ceramics. Especially, the BCZT–0.12NL ceramic displays a good recoverable energy density (Wrec) of 3.1J/cm3, a high efficiency of 86.7% (η) and a superior fatigue resistance, as well as a superior charge–discharge performance (CD～1623.14A/cm2, PD～162.31MW/cm3, WD～1.30J/cm3, t0.9～49.6ns) and good thermal stability. Besides, upon NL doping, the FE to RFE phase transition results in a dielectric behavior traversing the relaxation phase (γ～1.84) accompanied by frequency dispersion, which is beneficial to improve ESP. The superior ESP in this work indicates that BCZT–0.12NL ceramics are a promising candidate used in energy storage capacitors.

Polystyrene (PS) microspheres have the advantages of good stability, corrosion resistance and low density, which have a broad application prospect. In this paper, PS composite microspheres with 20% silver plating content were prepared by chemical plating method and incorporated into polydimethylsiloxane (PDMS) flexible matrix to prepare Ag@PS/PDMS flexible wave-absorbing materials. The electromagnetic parameters were adjusted to optimize the dielectric and wave-absorbing properties by varying the additional amount of Ag@PS composite microspheres in Ag@PS/PDMS composites. The X-ray diffraction (XRD) results proved the successful preparation of Ag@PS composite microspheres. The SEM and EDS images indicated that the Ag particles were attached to the external surface of PS. The presence of Ag particles in the Ag@PS composite microspheres enhances their electrical conductivity and enables the formation of a conductive network. This, in turn, improves the composites’ dielectric constant. The optimal wave-absorbing capability of the composites was achieved when the Ag@PS composite microspheres were added at a weight percentage of 50%. When the sample attains a thickness of 1.8mm, a reflection loss of at least ?39.8dB is attained at 10.4GHz, along with a bandwidth of 1.6GHz (9.1–10.7GHz) for the effective absorption bandwidth (EAB). The pressure-sensitive properties of the pliable composites were investigated as well. The optimal pressure-sensitive performance of Ag@PS/PDMS composites was achieved with a 60wt.% addition of Ag@PS composite microspheres. The resistance undergoes significant changes when subjected to pressure with a sensitivity of 9.7. The results indicate that the flexible composites’ wave-absorption and pressure-sensitivity properties can be modulated by adjusting the amount of Ag@PS composite microspheres added.

Pb(Mg0.5W0.5)O3–Pb(Ni1∕3Nb2∕3)O3–Pb(Zr0.5Ti0.5)O3 (PNN–PMW–PZT) piezoceramics were sintered at a low temperature of 900°C by the mixed metal oxide powder solid-state reaction route. CaCO3 and Li2CO3 as sintering aids and Yb2O3 as a dopant were added into the PNN–PMW–PZT ceramic system for low-temperature sintering and enhancement of electrical properties, respectively. The effects of different Yb2O3 doping amounts on the microstructure, dielectric, piezoelectric and ferroelectric properties of the samples were systematically investigated. The piezoceramics doped with 0.1mol% Yb2O3 have optimal electrical properties (d33=563pC/N, kp=0.66, εr=2728 (1kHz), tanδ=0.0176 (1kHz), and TC=301°C). While the piezoceramics doped with 0.3mol% Yb2O3 have optimal energy conversion properties: the piezoelectric voltage coefficient g33=26.7×10?3Vm/N and the effective piezoelectric energy conversion coefficient d33×g33=14366×10?15m2/N.

Bi0.5Na0.5TiO3 (BNT)-based lead-free ceramics with superior ferroelectric properties are considered to be extremely advantageous in energy storage capacitors for future green technologies. Here, we demonstrate an approach to achieve both ultrahigh energy density Wrec and efficiency η by regulating the multiscale electropolar structures and microstructure. A satisfactory energy storage performance of a high Wrec of 4.02J?cm?3, and a decent η of 80% under 415kV?cm?1 are attained in the 0.5(BNT-CS)-0.5SB0.2T ceramic (abbreviated as BNT-0.2SBT). Moreover, BNT-0.2SBT exhibits superior power density (PD=107MW?cm?3), ultrafast discharge time (t0.9=116ns) at 150kV?cm?1, and good temperature stability. The findings in this work not only demonstrate that a valid candidate, but also provide a new idea of how to achieve both high-energy storage density and efficiency in lead-free ferroelectric materials.

In order to improve the limited compatibility of existing polymer/ceramic dielectric composites and further enhance the energy storage density, MOF/polymer composite dielectrics have been explored, which exhibit good compatibility to the polymer matrix from abundant organic groups of the inorganic–organic hybrid metal-organic framework (MOF) fillers. However, they still lack a clear composition–structure–property rule, and the precise design of MOF fillers and polymer matrix becomes a prominent problem in these composites due to the diversity of the metal ions and the organic groups. Thus, in this paper, we present a series of formic acid MOFs/polylactic acid dielectric composites in which ferroelectric formic acid MOFs, namely PDLLA/[NH3(CH2)4NH3][MII(HCOO)3]2 and PDLLA/[CH3NH3][MII(HCOO)3]2, in which the formic acid MOFs are with different structures and different metal ions as fillers, including [NH3(CH2)4NH3][MII(HCOO)3]2 (namely MOF– Co (M = Co), MOF– Mg(M = Mg), MOF– Mn (M = Mn), with 1, 4-butanediamine ion as guest) and [CH3NH3][MII(HCOO)3]2 (namely MOF– Co2(M = Co), MOF– Ni2 (Ni), with methylamine ion as guest). The composition and morphology of composite films were characterized by XRD, IR, SEM, DSC and UV, respectively, while the dielectric characterizations of the composites including the dielectric permittivity, the dielectric loss, the breakdown field strength and the energy density were also performed. The composition–structure–property relationships were also investigated including the influence of MOF content and MOF category. With the introduction of MOFs, the dielectric constant of the polylactic acid substrate was improved slightly while the breakdown field strength can be improved in some systems. Interestingly, the Co(II)-containing formic acid MOF has advantages over other formic acid MOFs with similar structure for the enhancement of the dielectric constant and breakdown field strength. Also, in some composite films with methylamine ion guest MOF fillers and low-MOF content ( MOF– Co2 (1 vol.%) and MOF– Ni2 (1 vol.%)), the breakdown electric field enhanced significantly and further led to improved energy storage density which was about 43% higher than that of the polylactic acid matrix. The possible reason is that in these composites, the orientation of C–H bonds of MOFs seems more beneficial to the formation of hydrogen bonds between the carboxyl group of formic acid and the polylactic acid matrix. These relationships obtained from formic acid MOFs/polylactic acid composites are valuable to the design of high-performance polymer/MOF energy storage composites and may be a new perspective to the practical use of ferroelectric MOFs.

In this study, BNBT-KNN-xTa2O5 was designed and synthesized, successfully achieving a reduction in the relaxor-ferroelectric phase transition temperature. Synergy between temperature-dependent ferroelectric testing and dielectric spectroscopy confirmed that the depoling temperature gradually decreased with increasing doping concentration. Fitting of the relaxation parameter and freezing temperature substantiated that the incorporation of Ta2O5 increased the degree of relaxation in BNBT-KNN-xTa2O5, thereby effectively lowering the relaxor-ferroelectric phase transition temperature.

Developing environmental-friendly materials with high-density energy storage is of paramount importance to meet the burgeoning demands for energy storage. In this study, we harness the modulation of a multicomponent solid solution by introducing KNN as a third element into the BNT–BST system, thereby achieving a marked enhancement in both energy storage performance and the temperature stability of the dielectric constant. BNBST–4KNN stands out for its exceptional dielectric stability, with a dielectric constant variation rate within 10% across a broad temperature range of 40°C to 400°C, a feat attributed to the flattening and broadening of the Tm peak. BNBT–2KNN exhibits superior energy storage capabilities, with an energy storage density of 1.324 J/cm3 and an energy storage efficiency of 72.3%, a result of the P–E loop becoming more slender. These advancements are pivotal for the sustainable progression of energy storage technologies.

The development of multifunctional materials with optical and electrical properties has become a research hotspot in recent years. In this work, multifunctional 0.935(Bi0.5Na0.5)TiO3–0.065BaTiO3 (BNT–BT)-based ferroelectric ceramics doped with small amounts of CaMAlO4 (M=Dy, Ho) were prepared, and the effect of CaMAlO4 on the electrostrain and photoluminescence properties of the ceramics was studied. The results showed that the CaMAlO4 addition weakened the ferroelectric properties of the BNT–BT matrix, and promoted the improvement of the electrostrain performance. For samples doped with 1.5mol% CaMAlO4, the unipolar strain Suni reached the largest values, which were 0.33% (M=Dy) and 0.38% (M=Ho) under an electric field of 70kV/cm, corresponding to a large signal d33? (Smax∕Emax) of 471pm/V (M=Dy) and 543pm/V (M=Ho), respectively. In addition, due to the existing Dy3+ and Ho3+ luminescent ions, the modified samples exhibited excellent photoluminescence performance, which exhibited bright yellow emission (M=Dy) and green emission (M =Ho) under the blue excitation. Due to their multifunctional features, these materials have potential applications as “on-off” actuators, optical-electro integration and coupling devices.

This paper delves into the analysis of shear wave propagation with a sandwiched structure comprising a piezoelectric layer and an elastic layer, with a transversely isotropic layer in between. The frequency equation has been derived following Biot’s theory. The dimensionless phase velocities numerical values are computed and visually depicted to demonstrate their dependencies on anisotropy, piezoelectricity, initial stress and porosity in a comparative manner. The explicit demonstration of the relationship between each parameter and the geometry has been presented. The observation shows that as porosity in the medium increases, the phase velocity also increases. Furthermore, the existence of medium anisotropy results in a decrease in the phase velocity of shear waves. Moreover, a correlation is observed where higher tensile initial stress within the medium leads to a corresponding reduction in the phase velocity of shear waves. We conclude that considered parameters (viz. piezoelectricity, anisotropy, porosity, initial stress and thickness of layers) affect the velocity profile of the shear waves significantly. This study holds practical significance in the development of innovative-layered composites, surface acoustic wave (SAW) devices and sensors utilizing intelligent piezoelectric devices for engineering purposes.

Large-size electronic-grade polycrystalline silicon is an important material in the semiconductor industry with broad application prospects. However, electronic-grade polycrystalline silicon has extremely high requirements for production technology and currently faces challenges such as carbon impurity breakdown, microstructure and composition nonuniformity and a lack of methods for preparing large-size mirror-like polycrystalline silicon samples. This paper innovatively uses physical methods such as wire cutting, mechanical grinding and ion thinning polishing to prepare large-size polycrystalline silicon samples that are clean, smooth, free from wear and have clear crystal defects. The material was characterized at both macroscopic and microscopic levels using metallographic microscopy, scanning electron microscopy (SEM) with backscattered electron diffraction (EBSD) techniques and scanning transmission electron microscopy (STEM). The crystal structure changes from single crystal silicon core to the surface of the bulk in the large-size polycrystalline silicon samples were revealed, providing a technical basis for optimizing and improving production processes.

This paper focuses on the problems encountered in the production process of electronic-grade polycrystalline silicon. It points out that the characterization of electronic-grade polycrystalline silicon is mainly concentrated at the macroscopic scale, with relatively less research at the mesoscopic and microscopic scales. Therefore, we utilize the method of physical polishing to obtain polysilicon characterization samples and then the paper utilizes metallographic microscopy, scanning electron microscopy-electron backscatter diffraction technology, and aberration-corrected transmission electron microscopy technology to observe and characterize the interface region between silicon core and matrix in the deposition process of electronic-grade polycrystalline silicon, providing a full-scale characterization of the interface morphology, grain structure, and orientation distribution from macro to micro. Finally, the paper illustrates the current uncertainties regarding polycrystalline silicon.

High performance dielectric capacitors are ubiquitous components in the modern electronics industry, owing to the highest power density, fastest charge–discharge rates, and long lifetime. However, the wide application of dielectric capacitors is limited owing to the low energy density. Over the past decades, multiscale structures of dielectric ceramics have been extensively explored and many exciting developments have been achieved. Despite the rapid development of energy storage properties, the atomic structure of dielectric materials is rarely investigated. In this paper, we present a brief overview of how scanning transmission electron microscopy (STEM) is used as a tool to elucidate the morphology, local structure heterogeneity, atomic resolution structure phase evolution and the correlation with energy storage properties, which provides a powerful tool for rational design and synergistic optimization.

Interfacial engineering is important for ferroelectric thin-film heterostructures because of the modulation of boundary conditions of the spontaneous polarizations and their switching behaviors, which are essential for ferroelectric electronics. In this work, we study the effects of interfacial buffering layer, 5-nm-thick SrTiO3 (STO), on the imprint and domain switching of epitaxial Pt/Pb(Zr,Ti)O3/SrRuO3 (SRO) thin-film heterostructures and capacitors. By buffering the ultrathin SrTiO3 layer at the Pb(Zr,Ti)O3 surface, the imprint effect can be dramatically alleviated as observed in the piezoresponse force microscopy (PFM)-measured domain structures and polarization–electric field hysteresis loops in thin-film capacitors. However, when the SrTiO3 layer is buffered at the Pb(Zr,Ti)O3/SrRuO3 interface, the imprint effect is slightly increased. These phenomena are explained based on the band alignments among the Pt and SrRuO3 electrodes and the Pb(Zr,Ti)O3 layer associated with the existence of oxygen vacancies in the SrTiO3 layer. With the reduction of imprint effect, the domain switching dynamics are also improved in the SrTiO3-buffered Pb(Zr,Ti)O3 capacitor, in which the switching activation field is decreased by about 45.3% in comparison with that of the pristine capacitor. These results facilitate the design and optimization of ferroelectric devices with the improvements in domain configurations, switching behaviors and band alignments.

In this work, the frequency dependence of ferroelectric and electrocaloric properties in barium titanate-based ceramics was studied based on Maxwell relations. It is found that the maximum and remnant polarization will decrease while the coercive field increases a lot with rising frequency from 0.1 to 10Hz, indicating that polarization rotation and domain switching become difficult at high frequencies. The electrocaloric properties show the different frequency dependence at different phase structures. Isothermal entropy change (ΔS) and adiabatic temperature change (ΔT) are similar around/above Curie temperature (TC), showing tiny frequency dependence. However, ΔS and ΔT display the obvious frequency dependence below TC, especially in the orthorhombic–tetragonal phase-transition region with a stable ferroelectric phase, and this frequency dependence becomes more obvious under a low-electric field. It is also found that increasing the frequency can weaken the electric field dependence of electrocaloric strength. This work gives a general profile of frequency dependence for electrocaloric properties in ferroelectric ceramics.

Due to the strong magneto-elastic coupling in ferromagnetic/ferroelectric heterostructures and the potential applications in low-power magnetoelectric nanodevices, ferroelastic domains and the corresponding dynamic evolution under external stimuli have attracted intense research interest. Using pulsed laser deposition method, we have successfully grown layered-perovskite Bi2WO6 thin films on SrTiO3 (001) substrates. Interestingly, for the as-grown thin films with step-flow morphology, the relationship between ferroelastic domain number and size shows a normal distribution, which is similar to the Boltzman distribution for confined gas molecules at equilibrium. In addition, with post-annealing, the thin films with as-grown island-like morphology can be optimized for layered morphology, and the initial small ferroelastic domains can grow into large domains. This study provides an effective strategy for ferroelastic domain engineering, which can be applied for the design of multiferroic heterostructures and low-power nanodevices.

Ferroelectric materials are widely used in the applications of electronic devices due to their robust spontaneous polarization. The surface roughness of ferroelectric thin films, which is closely related to the morphology, can play an important role in determining the ferroelectric domain structures. In this work, we have investigated the influence of annealing conditions on the surface morphology of epitaxial BiFeO3 and SrRuO3 thin films prepared by pulsed laser deposition on SrTiO3 (001) substrates. It is found that the morphology of the thin films is sensitive to the annealing time and cooling rate, and the corresponding surface roughness decreases with increasing annealing time and decreasing cooling rate. In addition, the ferroelectric domain structures of BiFeO3 films have been investigated by piezoelectric force microscopy, which shows a significant improvement in domain size and reverse piezoelectric response in the thin films with decreasing surface roughness. This work provides a simple way to predict and improve the ferroelectric domain structures by in situ annealing.

The formation of the ferroelectric domain structure as a result of irradiation by focused ion beam of [100]-cut 0.61Pb(Mg1∕3Nb2∕3)O3–0.39PbTiO3 (PMN–PT) single crystals covered by surface artificial dielectric layer and with free surface was investigated. The dot irradiation resulted in formation of the wedge-like domains grown along [001?] direction. For irradiation of the free surface, the domains are mainly located under the surface, while at the irradiated surface with an artificial dielectric layer the domains are located at the surface. It was shown that the subsurface wedge-shaped part of the domain is unstable and completely disappears after a month due to spontaneous backswitching under the action of the residual depolarization field. The revealed nonlinear dose dependence of the domain sizes was attributed to the distribution of the electric field using the point charge model. The domain interaction for the distance between irradiated dots below 30μm has been revealed in all samples. It was shown that the decrease of the distance between irradiated dots in the created domain row leads to an increase in the length of the central domains, which is explained by the contribution of all injected charges to the switching field.

The creations and manipulations of vortexes in ferroelectric materials with external stimuli are expected to be used in the design and fabrication of sensing materials and multifunctional electronic devices. In this work, we investigated the surface charge-induced multi-vortex evolution using the phase-field simulations in BiFeO3. A combination of domain morphology, polarization distribution and winding number calculation was considered. The results show that vortex and anti-vortex exist simultaneously in pairs, and the total value of winding numbers is always 0. In addition, the minimum distance Δl between the surface charge regions is 9nm when the vortex domains are independent of each other. This work provides a reference for the manipulation of ferroelectric vortex induced by surface charges, which lays a theoretical foundation for the design and fabrication of high-density vortex memories.

Polymer-based dielectrics play an important role in electrostatic capacitor by their high energy density (Ue) and flexibility. Herein, we designed a simple high Ue polymer-based dielectrics by controlling the morphology and surface modification of inorganic fillers. To decrease the difference in dielectric properties between fillers and matrix of the nanocomposites, HfO2 acting as the buffer layer with high insulation and appropriate permittivity coated onto the surface of TiO2 nanosheets (TiO2 Ns) to form a core–shell structure. The introduction of HfO2@TiO2 nanosheets (HfO2@TiO2 Ns) makes the nanocomposite with higher dielectric permittivity and lower dielectric loss than poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) matrix. In addition, the HfO2@TiO2 Ns can establish an efficient barrier to limit the space charge conduction, hamper the growing electric trees, and the HfO2 layer with high insulation could hinder the mobility of charge carriers. The breakdown strength (Eb) of nanocomposite is superior to that of polymer matrix. A small addition of 3wt.% HfO2@TiO2 Ns into P(VDF-HFP) matrix can raise the Eb to 480.7MV/m and present a maximum discharged Ue of 13.9J/cm3. This work demonstrates that it is an effective strategy to improve the Ue via designing the structure and surface state of inorganic filler simultaneously.

Ferroelectric materials possessing exceptional piezoelectric attributes have garnered widespread utilization in various applications. Solid solution systems improve piezoelectric properties through multiphase mixing, but the methodologies for effective design remain wanting. Based on the Landau–Devonshire theory, we propose a theoretical design method. Binary materials with morphotropic phase boundary (MPB) compositions are added with new elements to increase the free energy of the original stabilized phase and lower the energy barrier (EB). Flatter EBsand higher piezoelectric coefficients are found at the phase boundaries of the ternary system. By calculating the phase diagram, piezoelectric coefficient, dielectric constant, polarization, and EBs, we reveal the origin of the highest piezoelectric coefficient at the phase boundaries. This study underscores the importance of the EBs for polarization rotation in characterizing piezoelectric properties and proposes a theoretical design method for exploring materials with high piezoelectric coefficients.

This review reports the latest trends in the ceramic composite matrix used for the magnetoelectric (ME) effect. In the last few years, ME composite has become the center of attraction for use in various electrically and magnetically coupled devices. The growth and use of electronic components everywhere have propulsively accelerated the exploration of self-powered electronic and sensor network devices. ME is a feasible technique for addressing difficulties of traditional batteries such as short life span and frequent recharge difficulties. Self-charging multiferroic components have been found for the constant working of mobile electronics that use multiferroic composites in response to magnetoelectric energy transformation. Researchers have rigorously studied the rigid and flexible magnetoelectric composites for their suitability in applications. This paper gives a comparative study between rigid and flexible magnetoelectric composites based on their properties and provides knowledge about the materials for such types of composites. It reviews the latest polymer-based ME materials as well as the related fabrication and polarization methods. The review finally encapsulates the applications in biomedicine, ranging from mechanical energy harvesters to sensors and actuators.

The solid solutions of the (1-x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3 system were produced by the conventional ceramic technology using mechanical activation of the synthesized product. It was found that in the (1-x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3 system at room temperature, a number of morphotropic phase transitions occur: rhombohedral → cubic → tetragonal → monoclinic phases. The introduction of a small amount of Na0.5K0.5NbO3 leads to an increase in the temperature stability of the dielectric properties of ceramics. A change in the relaxor properties of the solid solutions of the (1-x)Na0.5Bi0.5TiO3-xNa0.5K0.5NbO3 system was shown. The increase in energy density and energy efficiency was found at additive 10mol.% of Na0.5K0.5NbO3.

PbZrO3-based antiferroelectric (AFE) ceramics are promising dielectrics for high-energy-density capacitors due to their reversible phase transitions during charge–discharge cycles. In this work, a new composition series, [Pb0.93−xLa0.02(Li1∕2Bi1∕2)xSr0.04][Zr0.57Sn0.34Ti0.09]O3, with Li+ and Bi3+ substitution of Pb2+ at x=0, 0.04, 0.08, 0.12, 0.16 is investigated for the microstructure evolution, ferroelectric (FE) and dielectric properties. It is found that Li+ and Bi3+ substitution can significantly reduce the sintering temperature and simultaneously enhance the dielectric breakdown strength. An ultrahigh energy efficiency (94.0%) and a large energy density (3.22J/cm3) are achieved in the composition of x=0.12 with a low sintering temperature (1075∘C).

We studied the effect of titanium dioxide (TiO2) nanoparticles (NPs) on dielectric behavior of Na+ ion-conducting salt-complexed polymer nanocomposite system formed from a binary polymer blend of poly(ethylene oxide) (PEO) and polyvinyl pyrrolidone (PVP), with the addition of both sodium metaperiodate (NaIO4) at concentration 10wt.% and TiO2 NPs of size ∼10nm, at concentrations 1, 2, 3, 4 and 5wt.%. Free standing nanocomposite PEO/PVP/NaIO4/TiO2 films (150μm) were characterized at room-temperature by analyzing their complex electrical impedance and dielectric spectra in the range 1Hz–1MHz. At the concentration of 3wt.% of TiO2 NPs, both ion conductivity and dielectric permittivity of the PEO/PVP/NaIO4/TiO2 ion-conducting dielectrics reach an enhancement by more than one order of magnitude as compared to nanoadditive-free case.

In this paper, two optimized autofocusing metasurfaces (AFMs) with different desired focal distances are designed by using particle swarm optimization (PSO) algorithm. Based on the finite element simulation software COMSOL Multiphysics, the performance of ultrasound transducer (UT) with AFM at different design parameters in Airy distributions (r0,ω) and the bottom thickness (d) of AFM are simulated and analyzed. Based on the simulation data, the artificial neural network model is trained to describe the complex relationship between the design parameters of AFM and the performance parameters of UT. Then, the multiobjective optimization function for AFM is determined according to the desired performance parameters of UT, including focal position, lateral resolution, longitudinal resolution and absolute sound pressure. In order to obtain AFMs with the desired performance, PSO algorithm is adopted to optimize the design parameters of AFM according to the multiobjective optimization function, and two AFMs are optimized and fabricated. The experimental results well agree with the simulation and optimization results, and the optimized AFMs can achieve the desired performance. The fabricated AFM can be easily integrated with UT, which has great potential applications in wave field modulation underwater, acoustic tweezers, biomedical imaging, industrial nondestructive testing and neural regulation.

With the rapid development of modern industries, the high-temperature piezoelectric sensors that can work in extreme environments are in great demand. In this work, langasite (La3Ga5SiO14, LGS), as a high-temperature piezoelectric crystal with stable electro-elastic performance, is used as core element, and air and porous Al2O3 are selected as backing layers respectively to prepare two kinds of high-temperature acoustic emission (AE) sensors. The detection sensitivities at 25–500∘C are analyzed by the ball falling test and Hsu–Nielsen experiment. Under the condition of 25–500∘C, the received amplitude signals by both sensors are maintained above 90dB stimulated by the ZrO2 ceramic ball dropping. In the Hsu–Nielsen experiment, as the temperature rising from 25∘C to 500∘C, the signal amplitude of sensor with air backing layer decays from 447mV to 365mV, while the signal amplitude varies from 270mV to 203mV for the sensor with porous Al2O3 backing layer. Significantly, compared with the bandwidth of the air-backing sensor (37–183kHz), the sensor with porous Al2O3 backing layer broadens bandwidth to 28–273kHz. These results show that both these AE sensors have strong and stable response ability to AE signals at high-temperature of 500∘C. Therefore, piezoelectric AE sensor based on LGS has great potential application in the field of high-temperature structural health monitoring.

Flexoelectric effect describes the electromechanical coupling between the strain gradient and its internal polarization in all dielectrics. Despite this universality, the resulting flexoelectric field remains small at the macroscopic level. However, in nanosystems, the size-dependent effect of flexoelectricity becomes increasingly significant, leading to a notable flexoelectric field that can strongly influence the material’s physical properties. This review aims to explore the flexoelectric effect specifically at the nanoscale. We achieve this by examining strain gradients generated through two distinct methods: internal inhomogeneous strain and external stimulation. In addition, advanced synthesis techniques are utilized to enhance the properties and functionalities associated with flexoelectricity. Furthermore, we delve into other coupled phenomena observed in thin films, including the coupling and utilization of flexomagnetic and flexophotovoltaic effects. This review presents the latest advancements in these areas and highlights their role in driving further breakthroughs in the field of flexoelectricity.

Thin nanocomposite films based on tin dioxide with a low content of zinc oxide (0.5–5mol.%) were obtained by the sol–gel method. The synthesized films are 300–600nm thick and contains pore sizes of 19–29nm. The resulting ZnO–SnO2 films were comprehensively studied by atomic force and Kelvin probe force microscopy, X-ray diffraction, scanning electron microscopy, and high-resolution X-ray photoelectron spectroscopy spectra. The photoconductivity parameters on exposure to light with a wavelength of 470nm were also studied. The study of the photosensitivity kinetics of ZnO–SnO2 films showed that the film with the Zn:Sn ratio equal to 0.5:99.5 has the minimum value of the charge carrier generation time constant. Measurements of the activation energy of the conductivity, potential barrier, and surface potential of ZnO–SnO2 films showed that these parameters have maxima at ZnO concentrations of 0.5mol.% and 1mol.%. Films with 1mol.% ZnO exhibit high response values when exposed to 5–50ppm of nitrogen dioxide at operating temperatures of 200∘C and 250∘C.

Ferroelectric ceramics have the potential to be widely applied in the modern industry and military power systems due to their ultrafast charging/discharging speed and high energy density. Considering the structural design and electrical properties of ferroelectric capacitor, it is still a challenge to find out the optimal energy storage of ferroelectric ceramics during the phase-transition process of amorphous/nanocrystalline and polycrystalline. In this work, a finite element model suitable for the multiphase ceramic system is constructed based on the phase field breakdown theory. The nonlinear coupling relationship of multiple physical fields between multiphase ceramics was taken into account in this model. The basic structures of multiphase ceramics are generated by using the Voronoi diagram construction method. The specified structure of multiphase ceramics in the phase-transition process of amorphous/nanocrystalline and polycrystalline was further obtained through the grain boundary diffusion equation. The simulation results show that the multiphase ceramics have an optimal energy storage in the process of amorphous polycrystalline transformation, and the energy storage density reaches the maximum when the crystallinity is 13.96% and the volume fraction of grain is 2.08%. It provides a research plan and idea for revealing the correlation between microstructure and breakdown characteristics of multiphase ceramics. This simulation model realizes the nonlinear coupling of the multiphase ceramic mesoscopic structure and the phase field breakdown. It provides a reference scheme for the structural design and performance optimization of ferroelectric ceramics.

The paper presents the results of an experimental study of the local polarization reversal and creation of domains by a biased tip of scanning probe microscope (SPM) in lithium niobate single crystals of congruent composition with a surface layer modified by soft proton exchange (SPE). The depth dependence of H+ ions concentration in the SPE-modified layer measured by confocal Raman microscopy demonstrates a sufficient composition gradient. The creation of isolated domains and stripe domain structures has been done by two switching modes: (1) point switching by field application in separated points and (2) line scanning switching by motion of the biased tip being in contact with the sample surface. For point switching for pulse durations less than 10s, the logarithmic dependence of the domain diameter on the pulse duration was observed. The change of the dependence to a linear one for pulse duration above 10s has been attributed to the transition from the stochastic step generation at the domain wall to the deterministic one at the domain vertexes. The periodical structure of stripe domains was created in SPE CLN planar waveguides by scanning at elevated temperature. The revealed switching regime suppresses electrostatic interaction of neighboring domains and leads to a significant improvement of the domain structure regularity. The creation of the stable periodical domain structure with submicron periods in SPE CLN planar waveguides was demonstrated.

(Pb0.8Ba0.2)[(Zn1/3Nb2/3)0.7Ti0.3]O3 relaxor-type ferroelectric ceramics was obtained via classical solid-state reaction. The hysteresis loop results were discussed in the frame of ergodicity criterium around the characteristic ferroelectric relaxor freezing temperature. Slimer hysteresis loops were observed below the freezing temperature reflecting an ergodic relaxor behavior. Above this temperature, estimated around 223K for the studied system, larger and unsaturated like ferroelectric hysteresis loops were observed. This temperature also coincides with the slope change on maximum polarization and inflection point of remnant polarization curves. Energy storage, energy loss and efficiency values were determined in a wide temperature range. While the recoverable energy density shows relatively low values (0.23J/cm3), there are interesting behaviors for this parameter and for the efficiency, since the two physical quantities increase versus temperature and the efficiency even reaches the value of 97%.

BiFeO3–BaTiO3 is a promising lead-free piezoelectric ceramic, exhibiting high Curie temperature and superior electrochemical characteristics. In this work, (1−x)BiFeO3–xBaTiO3 (BF–xBT, x=0.26, 0.28, 0.30, 0.32, 0.34, 0.36) ceramics were fabricated using the conventional solid-state reaction method through precise composition control. Multiple characterization techniques, including X-ray powder diffraction (XRD), scanning electron microscope (SEM), and electrical property testing systems, were applied to systematically examine the crystallographic structure, microstructure, as well as the dielectric, ferroelectric and piezoelectric properties of the BF–xBT ceramics. The XRD results confirm that all compositions exhibit a typical perovskite structure, transitioning from a single rhombohedral phase to a rhombohedral–cubic phase mixture as the BT content increases. SEM shows apparent core–shell microstructures in the ceramics. Notably, the results demonstrated that the BF–0.30BT ceramic exhibits the maximum piezoelectric constant (d33) ∼217pC/N, while the BF–0.34BT ceramic displays the maximum converse piezoelectric constant (d33∗)∼323pm/V, which highlights the suitability of BF–BT ceramics for high-performance piezoelectric applications.

Monolayer molybdenum disulfide (MoS2) has weak light absorption due to its atomically-thin thickness, thus hindering the development of MoS2-based optoelectronic devices. CdSxSe1−x has excellent photoelectric performance in the visible light range, and its nanostructure shows great potential in new nanoscale electronic and optoelectronic devices. In this work, a composite photodetector device with the combination of monolayer MoS2 nanosheets and CdS0.42Se0.58 nanobelts has been successfully prepared, which can not only maintain the inherent excellent properties of the two blocks, but also play a synergistic role between them, thus improving the photoelectric performance of the device. The monolayer MoS2 nanosheet /CdS0.42Se0.58 nanobelt photodetector has a wide spectral response range (400–800nm), high responsivity (527.22A/W) and large external quantum efficiency (EQE) (1.06×105%). Compared with the isolated monolayer MoS2 nanosheet, both the responsivity and EQE of the hybrid photodetector are increased by 117.4 times under 620nm illumination. This study provides a way to prepare hybrid photodetectors with wide spectral response and high responsivity.

Ferroelectric nanocapacitors have attracted intensive research interest due to their novel functionalities and potential application in nanodevices. However, due to the lack of knowledge of domain evolution in isolated nanocapacitors, precise manipulation of topological domain switching in the nanocapacitor is still a challenge. Here, we report unique bubble and cylindrical domains in the well-ordered BiFeO3 nanocapacitor array. The transformation of bubble, cylindrical and mono domains in isolated ferroelectric nanocapacitor has been demonstrated via scanning probe microscopy (SPM). The bubble domain can be erased to mono domain or written to cylindrical domain and mono domain by positive and negative voltage, respectively. Additionally, the domain evolution rules, which are mainly affected by the depolarization field, have been observed in the nanocapacitors with different domain structures. This work will be helpful in understanding the domain evolution in ferroelectric nanocapacitors and providing guidance on the manipulation of nanoscale topological domains.

High-density ferroelectric BiFeO3 (BFO) nanodot arrays were developed through template-assisted tailoring of epitaxial thin films. By combining piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM) imaging techniques, we found that oxygen vacancies in nanodot arrays can be transported in the presence of an electric field. Besides triple-center domains, quadruple-center domains with different vertical polarizations were also identified. This was confirmed by combining the measurements of the domain switching and polarization vector distribution. The competition between the accumulation of mobile charges, such as oxygen vacancies, on the interface and the geometric constraints of nanodots led to the formation of these topological domain states. These abnormal multi-center topological defect states pave the way for improving the storage density of ferroelectric memory devices.

Two-dimensional α-In2Se3 exhibits simultaneous intercorrelated in-plane and out-of-plane polarization, making it a highly promising material for use in memories, synapses, sensors, detectors, and optoelectronic devices. With its narrow bandgap, α-In2Se3 is particularly attractive for applications in photodetection. However, relatively little research has been conducted on the out-of-plane photoconductive and bulk photovoltaic effects in α-In2Se3. This limits the potential of α-In2Se3 in the device innovation and performance modification. Herein, we have developed an α-In2Se3-based heterojunction with a transparent electrode of two-dimensional Ta2NiS5. The out-of-plane electric field can effectively separate the photo-generated electron–hole pairs in the heterojunction, resulting in an out-of-plane responsivity (R), external quantum efficiency (EQE), and specific detectivity (D*) of 0.78mA/W, 10−3% and 1.14×108 Jones, respectively. The out-of-plane bulk photovoltaic effect has been demonstrated by changes in the short circuit current (SCC) and open circuit voltage (Voc) with different optical power intensity and temperature, which indicates that α-In2Se3-based heterojunctions has application potential in mid-far infrared light detection based on its out-of-plane photoconductive and bulk photovoltaic effects. Although the out-of-plane photoconductive and bulk photovoltaic effects are relatively lower than that of traditional materials, the findings pave the way for a better understanding of the out-of-plane characteristics of two-dimensional α-In2Se3 and related heterojunctions. Furthermore, the results highlight the application potential of α-In2Se3 in low-power device innovation and performance modification.

Among the lead-free piezoceramics, (1−x)BiFeO3−xBaTiO3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature (TC>400∘C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO3 and BaTiO3, and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24h) of BiFeO3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO3 and BiFeO3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO3 increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO3–0.3BaTiO3 ceramics also improved. At the condition of a hydrothermal reaction time of 24h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant (Tkε=1.53×10−2/∘C between RT and 300∘C) and the highest Curie temperature (TC=471∘C at 100kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

Bi3.25La0.75Ti3O12(BLT) thin films are promising materials used in non-volatile memories. In this work, BLT films were deposited on Pt(111)/Ti/SiO2/Si substrates by rf-magnetron sputtering method followed by annealing treatments. The microstructures of BLT thin films were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). With the increase in annealing temperature, the grain size increased significantly and the preferred crystalline orientation changed. A well-saturated hysteresis loop with a superior remnant polarization of 15.4 μC/cm2 was obtained for BLT thin films annealed at 700°C. The results show that the dielectric constant decreased with the increase in grain sizes.

The lead-free ceramics (1?x)(0.94Bi0.47Na0.47Ba0.06TiO3-0.06BiAlO3)-xAgNbO3 (denoted as BNBTA-xAN) were synthesized via a solid-state sintering method. The effect of AgNbO3 doping amount on dielectric properties of the ceramics was studied systematically. X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectroscope were used to detect the structure of the ceramics. Temperature-dependent dielectric spectra, frequency-dependent dielectric constant and alternating current (ac) electric conductance at various temperatures were measured. The doping of AgNbO3 greatly reduces dielectric constant around Curie temperature and thus enhances the temperature stability of the dielectric constant. The ceramic BNBTA-0.03AN exhibits excellent temperature-stable dielectric properties with temperature coefficient of capacitance (TCC) ≤±15% between 55°C and 418°C with temperature window 363°C and small changes of dielectric constant and dielectric loss from 100 Hz to 1 MHz at different temperatures. The obtained ceramics are expected to be used in high-temperature capacitors due to its excellent temperature stability.

The photocatalytic water splitting kinetics has been analyzed in this paper. The experimental data are taken from the published works and fitted with different theoretical models. From the results, we find that the photocatalytic kinetics of water splitting can be described by Capelas-Mainardi–Vaz (CMV) model very well. This suggests that the water splitting kinetics can be regarded as a fractional first-order kinetics of the chemical reaction. Also, we notice that photocatalytic water splitting is not always completely a monotone kinetics process.

High entropy oxides (HEO) are single-phase solid solutions which are formed by the incorporation of five or more elements into a cationic sublattice in equal or near-equal atomic proportions. Its unique structural features and the possibility of targeted access to certain functions have attracted great interest from researchers. In this review, we summarize the recent advances in the electronic field of high-entropy oxides. We emphasize the following three fundamental aspects of high-entropy oxides: (1) The conductivity mechanism of metal oxides; (2) the factors affecting the formation of single-phase oxides; and (3) the electrical properties and applications of high-entropy oxides. The purpose of this review is to provide new directions for designing and tailoring the functional properties of relevant electronic materials via a comprehensive overview of the literature on the field of high-entropy oxide electrical properties.

We are examining the behavior of a composite made of ferroelectrics with strong dielectric properties and ferrites with magnetic properties due to the rising need for materials for multipurpose devices. Many application avenues will be favored by the pairing of these materials’ individual qualities with one another. Perovskite and U-type hexaferrite composite materials have been chosen for this study based on their magnetic and dielectric properties. The composites, (1?x) PLT?x(Ba1?3xNd2x)4Co2Fe36O60 where x = 0.52, 0.54, 0.56, 0.58 are prepared by solid state reaction method and phase formation was examined. Consideration has been given to the magnetic, dielectric, and magneto-dielectric properties. This work has established the link between the electric and magnetic domains while applying electric and magnetic forces to the materials. The magneto-dielectric research revealed magneto-electric coupling in all of the samples. However, the sample shows the maximum coupling for x = 0.54 with MDR% values of 93.17%, which might be because this sample appears to have a high magneto-resistance (161%).

Lead zirconate titanate (PZT) ceramics possess great potential for practical applications and thus improving their piezoelectric properties is crucial. Pb0.99?xSm0.01BaxZr0.53Ti0.47O3 (PSBZT) ceramics with high Curie temperature and excellent piezoelectric properties were fabricated via a conventional solid-state method, and the effect of Ba2+ doping on the structural, dielectric, piezoelectric and ferroelectric properties was studied in detail. It is shown that doping of Ba2+ significantly enhanced the piezoelectric properties of PSZT, the maximum d33～533 pC/N and Tc～361°C at x= 0.02 were acquired. Furthermore, PSZT and PSBZT ceramics were used to prepare single element ultrasonic transducers, and their performance were compared and evaluated. The results demonstrate that the PSBZT ceramic-based transducer possesses better sensitivity and bandwidth than the PSZT ceramic-based transducer.

CaCu3Ti4O12 (CCTO) is a potential dielectric material with giant permittivity, good stability over the wide temperature and frequency range. However, the dielectric responses of CCTO-based ceramics are mainly investigated in the frequency of 10 2–106 Hz, which is far low to clarify the intrinsic dielectric feature. So, microwave dielectric properties have been investigated for the CCTO porous ceramics sintered at low temperature (≤1000°C). Good microwave dielectric properties of permittivity ?? = 62.7, quality factor Qf = 3062 GHz and temperature coefficient of the resonant frequency τf = 179 ppm/°C are achieved for the CCTO ceramics sintered at 1000°C, the dielectric loss significantly decreases two orders to 0.002 compared to that of CCTO ceramics sintered at critical temperature of 1020°C confirmed by differential scanning calorimetry (DSC). This clue indicates that giant permittivity and high loss is not intrinsic for CCTO ceramics, but derives from composition segregation, liquid phase and defects associated with internal barrier layer capacitor (IBLC). It suggests that CCTO-based ceramics is a promising microwave dielectric materials with high permittivity.

Dielectric capacitors are receiving increasing attention due to the high-power density and fast charge–discharge speed. However, defects are inevitably induced during the preparation process and then weaken the breakdown strength, thereby limiting their energy density. The phenomenon gives rise to self-healing technology. The discovery of sol–gel-derived aluminum oxide with electrolysis and dielectric dual-characteristic provides a novel, simple and cost-effective self-healing method to heal defects and enhance energy density. In this paper, we systematically reviewed the current self-healing technologies and the important progress of electrolysis and dielectric co-existence dielectrics. Finally, we outlook the electrolysis and dielectric co-existence dielectrics and potential challenge.

This paper reviews the interpretation of impedance and capacitance spectra for different capacitor technologies and discusses how basic electrical characteristics can be inferred from them. The basis of the interpretation is the equivalent circuit for capacitors. It is demonstrated how the model parameters, such as capacitance and equivalent series resistance, can be extracted from the measured spectra. The aspects of measurement accuracy are exemplarily discussed on the measured spectra.

Nowadays, the demand for advanced functional materials in transducer technology is growing rapidly. Piezoelectric materials transform mechanical variables (displacement or force) into electrical signals (charge or voltage) and vice versa. They are interesting from both fundamental and application points of view. Ferrooelectrets (also called piezoelectrets) are a relatively young group of piezo-, pyro- and ferroelectric materials. They exhibit ferroic behavior phenomenologically undistinguishable from that of traditional ferroelectrics, although the materials per se are essentially non-polar space-charge electrets with artificial macroscopic dipoles (i.e., internally charged cavities). A lot of work has been done on ferroelectrets and their applications up to now. In this paper, we review and discuss mostly the work done at University of Potsdam on the research and development of ferroelectrets. We will, however, also mention important results from other teams, and prospect the challenges and future progress trend of the field of ferroelectret research.

The theory and application of resonances and vibrational modes are part of the foundation of science. In this contribution, examples of acoustical resonators are highlighted, and compared to electromagnetic modes. As an example from architecture, we describe the phenomenon of whispering galleries; such modes are nowadays known in dielectric and optical resonators. A specimen of a semicircular whispering bench in Park Sanssouci in Potsdam is acoustically investigated and demonstrated to show low losses for sound propagation. A special acoustical bug is discussed which was used for the espionage of the U.S. ambassador in Moscow. The Sovyets could interrogate this passive device by radio waves. Its working principle was based on the electromagnetic resonance of the cavity that the sound-sensitive membrane was part of. The underlying relation between excitation and resonance is compared to the sound production in flue organ pipes. A stopped flue organ pipe was investigated using a piezoelectric film sensor inside the pipe body. The results show that even-numbered modes, which are usually suppressed in the radiated sound of a stopped pipe, are still present in the vibrations inside the resonator.

More than 30 years ago, a group of researchers in Tampere–Finland developed a thin foamed polymeric material for capacitive sensors. Such soft-voided films exhibited electrical charging characteristics, forming a powerful combination, which resulted in a smart-material with ferroelectric properties. The discovery of the electro-thermo mechanical film (ETMF) has sparked the curiosity of the electret community, leading to the development of several studies. At that time, ETMF became known as cellular electrets and, later, as ferroelectrets or piezoelectrets regarding their electromechanical properties. This paper provides a timeline review of the research on ferroelectrets produced in Brazil, between the years 1990 and 2020, towards demonstrating how the interest in the electret electrical charging mechanism has resulted in the use of ferroelectrets with well-controlled cavities for ultrasound applications.

Vinylidene fluoride-trifluoroethylene copolymer films of molar ratio 70/30 with thickness of about 1 μm have been deposited from solution in ethyl methyl ketone to a glass substrate with an aluminum electrode by spin coating. The solution has been filtrated through a PTFE membrane filter with pore size 0.2 μm directly before spin coating or it has been used as is (unfiltrated). After deposition of a top electrode, the samples have been polarized by hysteresis loops with an electric field amplitude of about 100 V/μm. In samples, annealed at temperature 145∘C for 3 h, a high remanent polarization of about 7.5 μC/cm2 has been achieved, without significant differences between samples fabricated of filtrated or unfiltrated solution. Spherulitic lamella are growing in films fabricated of filtrated solution when they are heated above the melting temperature to 159∘C for 3 min before the further annealing process at 145∘C. These films show substantially lower remanent polarization below 4 μC/cm2. Pyroelectric images recorded with a pyroelectric laser scanning microscope show that the spherulites have very small pyroelectric activity, i.e., the spherulites consist of flat-on lamella. In contrast, no spherulitic lamella are growing in films fabricated of unfiltrated solution heated above the melting temperature, melted and annealed under the same conditions. An explanation for this observation is that filtrating changes the structure of the copolymer in solution from polymer coil to rod. Copolymer rods deposited on a substrate will crystallize in flat-on lamella when heated above the melting temperature, in contrast to copolymer coils which crystallize in edge-on lamella.

Flexible dielectric polymers that can withstand high electric field and simultaneously have high dielectric constant are desired for high-density energy storage. Here, we systematically investigated the impact of oxygen-containing ether and carbonyl groups in the backbone structure on dielectric properties of a series of cyclic olefin. In comparison to the influence of the –CF3 pendant groups that had more impact on the dielectric constant rather than the band gap, the change of the backbone structure affected both the dielectric constant and band gaps. The one polymer with ether and carbonyl groups in the backbone has the largest band gap and highest discharge efficiency, while it has the lowest dielectric constant. The polymer without any ether groups in the backbone has the smallest band gap and lowest discharge efficiency, but it has the highest dielectric constant. Polymers that have no dipolar relaxation exhibit an inversely correlated dielectric constant and band gap. Enhancing the dipolar relaxation through rational molecular structure design can be a novel way to break through the exclusive constraint of dielectric constant and band gap for high-density energy storage.

Ferroelectricity in biological system has been anticipated both theoretically and experimentally over the past few decades. Claims of ferroelectricity in biological systems have given rise to confusion and methodological controversy. Over the years, a “loop” of induced polarization in response to a varying applied electrical field and a consequent polarization reversal has prompted many researchers to claim ferroelectricity in biological structures and their building blocks. Other observers were skeptical about the methodology adopted in generating the data and questioned the validity of the claimed ferroelectricity as such, “loop” can also be obtained from linear capacitors. In a paper with somewhat tongue-in-cheek title, Jim Scott showed that ordinary banana peels could exhibit closed loops of electrical charge which closely resemble and thus could be misinterpreted as ferroelectric hysteresis loops in barium sodium niobate, BNN paraphrasing it as “banana”. In this paper, we critically review ferroelectricity in biological system and argue that knowing the molecular and crystalline structure of biological building blocks and experimenting on such building blocks may be the way forward in revealing the “true” nature of ferroelectricity in biological systems.

Lead-free piezoelectric sodium bismuth titanate ((Bi0.5Na0.5)TiO3, BNT) thin films were epitaxially grown onto (001)-, (110)-, and (111)-oriented Nb:SrTiO3 (STO) single crystal substrates prepared by sol–gel processing. Highly oriented growth in (001), (110), and (111) BNT thin films was obtained in this work benefiting from the lattice match between the BNT film and the STO substrate. The different growth models in thin films with various orientations result in various surface morphologies dependent on the film orientation. The piezoresponse of the BNT thin films was represented exhibiting a strong orientation dependence that (110)>(001)>(111). This is contributed by the various domain switching contribution related to the crystal symmetry and polarization distribution in the three oriented thin films.

The characterization of pyroelectric materials is essential for the design of pyroelectric-based devices. Pyroelectric current measurement is the commonly employed method, but can be complex and requires surface electrodes. Here, we present noncontact electrostatic voltmeter measurements as a simple but highly accurate alternative, by assessing thermally-induced pyroelectric surface potential variations. We introduce a refined model that relates the surface potential variations to both the pyroelectric coefficient and the characteristic figure of merit (FOM) and test the model with square-shaped samples made from PVDF, LiNbO3 and LiTaO3. The characteristic pyroelectric coefficient for PVDF, LiNbO3 and LiTaO3 was found to be 33.4, 59.9 and 208.4 μC m−2 K−1, respectively. These values are in perfect agreement with literature values, and they differ by less than 2.5% from values that we have obtained with standard pyroelectric current measurements for comparison.

Dielectric materials with high energy storage density (Wrec) and efficiency (η) are expected for energy storage capacitors. In this work, 〈001〉-textured Na0.7Bi0.1NbO3 (NBN) ceramics were prepared by a templated grain growth technique. The effects of microstructure and orientation degree on dielectric properties, polarization and energy storage performance were investigated. The textured ceramic with an optimized orientation degree (70%) showed a high Wrec of 2.4 J/cm3 and η of 85.6%. The excellent energy storage properties of textured ceramic originate from the co-effect of interfacial polarization and clamping effect. The results indicate that texture development is a potential candidate to optimize the energy storage properties of functional ceramics.

In this report, the processes of texture formation in grain-oriented ferroelectric ceramics based on layer-structured ferroelectric Bi4Ti3O2 (LSBT) prepared by hot forging method are considered. The microstructural and X-ray methods revealed the axial textured formation in ferroelectric ceramic that are used to estimate the orientation factor of ceramics. For the first time, the domain structure changes when poling the anisotropic ferroelectric ceramics are investigated. The anisotropy of electromechanical, piezoelectric and ferroelectric properties of ferroelectric ceramics due to the crystal texture existence in it is studied. The aim of this study is to study the processes of crystalline texture formation in polycrystalline BLSF and to establish the dependence of the electrophysical properties of ceramics on the degree of texturing. Ceramics were textured using the hot stamping (HS) method developed at the Research Institute of Physics. The mechanism of the method is that the workpiece is subjected to uniaxial pressure and free radial deformation occurs due to the plastic flow of the material until the workpiece fills the free volume of the mold, which is created by placing the workpiece in the mold with a gap. The study of the microstructure of ceramics showed that an increase in the firing temperature in the range 950–1050∘C causes a sharp decrease in porosity and increases the density to 7.95 g/cm3, which is 98% of theoretical. An X-ray analysis was performed and microstructural studies were carried out, which revealed the formation of an axial texture in ceramics. The features of the switching processes of textured ceramics are revealed. The characteristics of the polarization switching of ceramics in the directions parallel and perpendicular (⊥) of the pressure axis during hot processing were obtained from the dielectric hysteresis P(E) loops, i.e., axis axial texture. The ⊥-cut ceramics are characterized by a more complete polarization switching, which is associated with the additional orientation of the (001) crystallographic planes in the textured material, as well as the presence of a threshold switching field. In the temperature range from -196 to + 600∘C, the anisotropy of the electro physical properties of ceramics due to the presence of a crystalline texture in it was studied. The dielectric constant, electrical conductivity, piezoelectric and elastic coefficients were measured for sections of ceramics of different orientations relative to the axis of the texture. The anisotropy of the dielectric constant and electrical conductivity manifests itself weakly at room temperature and increases sharply when approaching the Curie temperature. In the temperature range +20–400∘C, the high thermal stability of the piezoelectric module d33, measured by the quasistatic method, was established.

Lead-free (K0.5Na0.5)NbO3 (KNN) and Li0.06(K0.5Na0.5)0.94NbO3 (LKNN) thin films were fabricated by a sol-gel method. The effects of Li substitution on crystal structure, microstructure and electrical properties of KNN film were systematically studied. Li doping can enhance the ferroelectric and piezoelectric properties of KNN film. Compared with pure KNN film, the LKNN film possesses larger remanent polarization (Pr∼ 9.3 μC/cm2) and saturated polarization (Ps∼ 41.2 μC/cm2) and lower leakage current density (∼10−5A/cm2 at 200 kV/cm). Meanwhile, a typical butterfly shaped piezoelectric response curve is obtained in the LKNN film with a high piezoelectric coefficient (d33∼ 105 pm/V). Excellent fatigue resistance (∼109 switching cycles) and aging resistance (∼ 180 days) demonstrate the long-term working stability of LKNN film. These findings indicate that KNN-based lead-free piezoelectric films have a broad application prospect in microelectromechanical systems (MEMS).

Enhancing the availability and reliability of dielectric ceramic energy storage devices is of great importance. In this work, (1-x)Na0.5Bi0.5TiO3–xBi(Mg0.5Hf0.5)O3 (NBT–xBMH) lead-free ceramics were created utilizing a solid-state reaction technique. All NBT–xBMH ceramics have a single perovskite structure. With increasing BMH doping, the grain size shrinks drastically, which greatly enhances the breakdown electric field (310 kV/cm at x = 0.25). Additionally, the relaxation behaviors of NBT–xBMH ceramics with high BMH content are more remarkable. Among all designed components, the NBT–0.25BMH ceramic exhibits the best energy storage performance with a high Wrec of 4.63 J/cm3 and an η of 75.1% at 310 kV/cm. The NBT–0.25BMH ceramic has exceptional resistance to fluctuations in both frequency (5–500 Hz) and temperature (30–100∘C). Charge–discharge test shows that the NBT–0.25BMH ceramic has a quick discharge rate (t0.9< 110 ns). With these properties, the NBT–0.25BMH ceramic may have applications in microdevices as well as in ultra-high power electronic systems.

MnO2-modified Pb0.9625Sm0.025(Mg1/3Nb2/3)0.71Ti0.29O3 ceramics were prepared via a solid-state reaction approach. Results of detailed characterizations revealed that the addition of MnO2 has influence on the grain size, and all samples exhibit a pure perovskite structure. As the content of manganese increases, the volume of tetragonal phase increases. The ceramics with 1.5 mol.% MnO2 show a high electro-strain of 0.151% at 2 kV/mm. Therefore, this study provides a new insight into the role of MnO2 addition in tailoring the electrical properties of the Sm-PMN-PT ceramics by acceptor doping.

We report a straightforward tool to investigate insulator-metal transition in RCoO3 (R = Pr, and Nd) nanoparticles prepared by a sol–gel technique. Thermogravimetric analysis (TGA) of the as-prepared gel is performed to get the lowest possible calcination temperature of RCoO3 nanoparticles. The Rietveld refinement of the powder X-ray diffraction (XRD) patterns for both samples shows that the samples crystallize in the orthorhombic (Pnma) phase at room temperature. The particle size of the sample is determined by scanning electron microscopy. Ac conductivity of the materials is analyzed in the temperature range from 303 K to 673 K and in the frequency range from 42 Hz to 1.1 MHz. The insulator-to-metal transition of PrCoO3 and NdCoO3 is analyzed by ac impedance spectroscopy. DC resistivity measurement is also done to cross check the insulator-metal transition in RCoO3 system.

The domain wall structure of ferroelectric/ paraelectric superlattices can be much more complex due to the influence of the superlattice stacking structure, the in-plane strain induced by the substrate and environmental temperature. In this study, we employed a phase field model to investigate the domain wall state of the SrTiO3/BaTiO3 superlattice structure. The domain wall thickness for the SrTiO3/BaTiO3 layer was measured using a hyperbolic function. Based on the simulation results, here, we show a domain wall state diagram to distinguish the hard and soft domain states. The polarization profiles across hard/ soft domain walls were illustrated and analyzed. Our simulation results offer a useful concept for the control of the domain wall state in the ferroelectric superlattice.

High-quality single crystals of Bi2WO6 are grown using a flux method. With different flux growth recipes, we aim to control the crystallization temperature to be lower and higher than the ferroelectric transition temperature, resulting in mono-domain and multi-domain Bi2WO6 crystals, respectively. Abundant ferroelastic orthorhombic twin domains are observed in the multi-domain crystals under an optical microscope. PFM studies unveil the 90∘ polarization change across those ferroelastic domain walls, as well as the absence of 180∘ ferroelectric domains in the as-grown multi-domain crystals, indicating a high energy cost of 180∘ ferroelectric domains. Moreover, a 45∘ tilt of the 90∘ ferroelectric domain walls is discovered, and this tilt creates a new type of charged 90∘ ferroelectric walls, which have not been observed in other bulk ferroelectrics.

Driven by the minimization of total energy, the multi-domain morphology is preferred in as-grown ferroelectrics to reduce the depolarization and strain energy during the paraelectric to ferroelectric phase transition. However, the complicated multi-domain is not desirable for certain high-performance ferroelectric electro-optic devices. In this work, we achieve a reproducible and stable large-area monodomain in as-grown bulk ferroelectric single crystal Sn2P2S6. The monodomain dominates the entire single crystal, which is attributed to the internal charge carriers from the photoexcited disproportionation reaction of Sn ions. The charge carriers effectively screen the depolarization field and therefore decrease the depolarization energy and facilitate the formation of monodomain. This work offers a potential approach for engineering bulk ferroelectrics with a stable monodomain, which is desirable for the high-performance ferroelectric electro-optic devices.

In this paper, Lead-free based on 0.97(K0.48Na0.48Li0.04)(Nb0.8Ta0.2)O3–0.03Bi0.5Na0.5TiO3 with additives La2O3 (1, 2, 3, 4 wt.%) was prepared by the solid reaction method, and the effect of La dopant on the structural and electrical properties is investigated. The result indicates La dopant considerably decreases the optical band gap compared to the undoped composition. On the other hand, La doping leads to the higher dielectric property in a wider temperature, providing possibilities and directions for the subsequent development of ferroelectric photovoltaic materials with electrical properties and low optical band gap in a dramatical manner.

The purpose of this work is to study the processes of interfacial interactions, their influence on the piezoelectric properties in highly elastic composite structures, to establish the patterns that determine the volume-sensitive piezoelectric characteristics of composites and to create effective piezoelectric materials for hydroacoustic receiving devices. In the process of this work, the development of a method for obtaining anisotropic ferropiezoelectric ceramics, the development of methods for the preparation of perfect ceramic powders and composite materials based on thermoplastic fluoropolymers and the study of composite materials based on lead–calcium titanate were carried out. As a result of the study, the dependences of the hydrostatic parameters of the composites on the degree of filling, particle size distribution, piezoelectric anisotropy of the active phase and the elastic properties of the polymer matrix were established. Composite materials were based on ceramics of the PT–CT system and thermoplastic fluoropolymers F-2ME, F-62, F-2N with a degree of filling with a ceramic phase from 30 to 60% vol. The dependences of the hydrostatic piezoelectric moduli gh and dh, and the quality factor gh⋅dh on the degree of filling of the composite for polymers F-62 and F-2ME with different average sizes of ceramic particles are plotted. It has been established that the maximum values gh = 119.1⋅10−3V⋅m/N and the quality factor gh⋅dh = 6074⋅10−15 m2/N are achieved for a polymer with a higher elastic compliance (F-62) at a degree of filling of 60% vol. and the use of granular filler.

The polarization orientation effect and porosity effect on the piezoelectric properties and related parameters are studied in 2–2-type composites based on domain-engineered relaxor-ferroelectric [011]-poled single crystals. The parameters, which are of great interest, are an anisotropy of the piezoelectric coefficients d3j*, an anisotropy of the energy-harvesting figures of merit d3j*g3j* and the hydrostatic piezoelectric coefficient dh*. An orientation of the main crystallographic axes in each polydomain single-crystal layer is described by angles β and γ. Diagrams built for the first time show the (β,γ) regions, where a large anisotropy of d3j* (or d3j*g3j*) is achieved, and where inequality dh*> 1000 pC/N holds. A large local max dh* = 1930 pC/N is achieved in a 2–2–0 PZN–0.065PT-based composite at the longitudinal piezoelectric coefficient d33* = 2290 pC/N and figure of merit d33*g33* = 1.02.10 − 9 Pa − 1. The aforementioned large parameters are to be of value in piezoelectric sensing, energy harvesting and hydroacoustics.

B0.77Ca0.23TiO3 (BCT) single crystal has been widely studied as a promising lead-free ferroelectric material. In this work, high-quality BCT crystal was successfully grown by the Czochralski (CZ) method. The as-grown crystal is crack-free and shows black coloration. It possesses a high dielectric stability over a wide temperature range, while the dielectric loss is rather small below 90∘C. Furthermore, it possesses excellent ferroelectric properties with residual polarization strength (Pr) and coercive field (Ec) of 17.93 μC/cm2 and 8.47 kV/cm, respectively. Besides, BCT crystal shows large electromechanical coupling factors, with kt, k31, k33 and k15 of 0.535, 0.254, 0.714 and 0.721, respectively. The piezoelectric coefficients d31, d33 and d15 are measured to be − 36.5, 130 and 246 pC/N, respectively.

Most widely used dielectrics for MLCC are based on BaTiO3 composition which inevitably shows performance degradation during the application due to the migration of oxygen vacancies (Vo⋅⋅). Here, the BaTiO3, (Ba0.97Ca0.03)TiO3, Ba(Ti0.98Mg0.02)O3, (Ba0.97Ca0.03)(Ti0.98Mg0.02)O3, (Ba0.96Ca0.03Dy0.01)(Ti0.98Mg0.02)O3 ceramics (denoted as BT, BCT, BTM, BCTM and BCDTM, respectively) were prepared by a solid-state reaction method. The core-shell structured grains (∼200 nm) featured with 10-20 nm wide shell were observed and contributed to the relatively flat dielectric constant-temperature spectra of BTM, BCTM and BCDTM ceramics. The TSDC study found that the single/ mix doping of Ca2+, especially the Mg2+, Mg2+/Ca2+ and Mg2+/Ca2+/Dy3+ could limit the emergence of Vo⋅⋅ during the sintering and suppress its long-range migration under the electric-field. Because of this, the highly accelerated lifetimes of the ceramics were increased and the value of BCDTM is 377 times higher than that of BT ceramics. The p−n junction model was built to explain the correlation mechanism between the long-range migration of Vo⋅⋅ and the significantly increased leakage current of BT-based dielectrics in the late stage of HALT.

The paper reports results on the complex study on ferroelectric ceramics that represent solid solutions containing components with a perovskite-type or columbite-type structure. Solid solutions of a three-component (1−x−y)NaNbO3−xKNbO3−yCdNb2O6 system are manufactured at x = 0.05–0.20 and y = 0.10. Domain structures in ceramic grains are studied. The consistency between experimental and calculated results is examined for coexisting phases split into non-180∘ domains (mechanical twins) in the solid solution with x = 0.15. A correlation between the internal structure (crystal, domain, granular, and defect) and fundamental electromechanical and polarization properties is stated for the studied three-component solid solutions.

Plate-like single-crystalline BaBi4Ti4O15 particles were synthesized by the molten salt synthesis (MSS) method. The effects of sintering temperature, holding time, and NaCl–KCl molten salt content on the phase structure and morphology of plate-like BaBi4-Ti4O15 particles were investigated. The results show that plate-like BaBi4Ti4O15 particles can be synthesized when the sintering temperature is above 800∘C. The size of particles increases with increasing sintering temperature and molten salt content. Largely anisotropic plate-like BaBi4Ti4O15 particles with diameter ≥10μm and thickness of ∼0.3 μm can be obtained under the optimum process parameters. The crystal structure of BaBi4Ti4O15 was determined as A21am by TEM, which should be attributed to the Bi3+ and Ba2+ diffusing into [TiO6] octahedrons.

One of the key points in the physics of the relaxors is their response to the applied DC field. Many studies of this topic were made, in particular on the influence of the field on the dielectric properties. However, practically, in all the cases, the measurements were performed at a fixed frequency and usually with the change in the temperature at the fixed field strength. In this paper, we report the evolution of the dielectric spectra at low frequencies (0.1 Hz <ω< 1 kHz) at fixed temperature 246 K on changing the DC electric field applied in (111) from 1 kV to 7 kV. Cole-Cole function was used to describe the spectra and the field dependences of the mean relaxation time τ, the oscillation strength Δ𝜀 and the width parameter α were determined. The obtained τ(E) and Δ𝜀(E) provide evidence of the field-induced transition from the nonpolar glass-like phase to the nonpolar paraelectric phase at around 1.5 kV/cm. In the paraelectric phase, very fast hardening of the spectra was observed with τ changing from 10 s to about 10−4s. The performed analysis demonstrated that the earlier reported positive C-V effect is completely determined by the spectra hardening, while Δ𝜀 does not show any change in the glass-like phase and monotonously decreases with a field increase in the paraelectric state. For complete understanding of the microscopic origin of the observed phenomena, a detailed study on the short-and long-range structures at the same condition is necessary.

Dielectric capacitors with high capacitive energy storage are urgently needed to meet the growing demand for high-performance energy storage devices. Herein, a novel lead-free Sr5BiTi3Nb7O30 (SBTN) tungsten bronze relaxor ferroelectric ceramic is prepared and explored for potential energy storage applications. A high recoverable energy densityWrec (∼ 3.72 J/cm3) and ultrahigh efficiencyη (∼ 94.2%) at 380 kV/cm are achieved simultaneously. BothWrec andη exhibit superior stabilities against temperature (30–140∘C), cycles (100 –105) and frequency (1–500 Hz). In addition, a high current density of 796 A/cm2 and a large power density of 71.7 MW/cm3 are achieved, together with good thermal endurance and fatigue resistance. These results demonstrate that the obtained SBTN ceramic can be deemed as the promising candidates for dielectric capacitor applications.Dielectric capacitors with high capacitive energy storage are urgently needed to meet the growing demand for high-performance energy storage devices. Herein, a novel lead-free Sr5BiTi3Nb7O30 (SBTN) tungsten bronze relaxor ferroelectric ceramic is prepared and explored for potential energy storage applications. A high recoverable energy densityWrec (∼ 3.72 J/cm3) and ultrahigh efficiencyη (∼ 94.2%) at 380 kV/cm are achieved simultaneously. BothWrec andη exhibit superior stabilities against temperature (30–140∘C), cycles (100 –105) and frequency (1–500 Hz). In addition, a high current density of 796 A/cm2 and a large power density of 71.7 MW/cm3 are achieved, together with good thermal endurance and fatigue resistance. These results demonstrate that the obtained SBTN ceramic can be deemed as the promising candidates for dielectric capacitor applications.

Flexible dielectric materials with environmental-friendly, low-cost and high-energy density characteristics are in increasing demand as the world steps into the new Industrial 4.0 era. In this work, an elastomeric nanocomposite was developed by incorporating two components: cellulose nanofibrils (CNFs) and recycled alum sludge, as the reinforcement phase and to improve the dielectric properties, in a bio-elastomer matrix. CNF and alum sludge were produced by processing waste materials that would otherwise be disposed to landfills. A biodegradable elastomer polydimethylsiloxane was used as the matrix and the nanocomposites were processed by casting the materials in Petri dishes. Nanocellulose extraction and heat treatment of alum sludge were conducted and characterized using various techniques including scanning electron microscopy (SEM), thermogravimetric analysis/derivative thermogravimetric (TGA/DTG) and X-ray diffraction (XRD) analysis. When preparing the nanocomposite samples, various amount of alum sludge was added to examine their impact on the mechanical, thermal and electrical properties. Results have shown that it could be a sustainable practice of reusing such wastes in preparing flexible, lightweight and miniature dielectric materials that can be used for energy storage applications.Flexible dielectric materials with environmental-friendly, low-cost and high-energy density characteristics are in increasing demand as the world steps into the new Industrial 4.0 era. In this work, an elastomeric nanocomposite was developed by incorporating two components: cellulose nanofibrils (CNFs) and recycled alum sludge, as the reinforcement phase and to improve the dielectric properties, in a bio-elastomer matrix. CNF and alum sludge were produced by processing waste materials that would otherwise be disposed to landfills. A biodegradable elastomer polydimethylsiloxane was used as the matrix and the nanocomposites were processed by casting the materials in Petri dishes. Nanocellulose extraction and heat treatment of alum sludge were conducted and characterized using various techniques including scanning electron microscopy (SEM), thermogravimetric analysis/derivative thermogravimetric (TGA/DTG) and X-ray diffraction (XRD) analysis. When preparing the nanocomposite samples, various amount of alum sludge was added to examine their impact on the mechanical, thermal and electrical properties. Results have shown that it could be a sustainable practice of reusing such wastes in preparing flexible, lightweight and miniature dielectric materials that can be used for energy storage applications.

In this work, novel (1 − x)(0.75Na0.5Bi0.5TiO3)-0.25Sr(Zr0.2Sn0.2Hf0.2Ti0.2Nb0.2)O3-xNaNbO3 (NBT-SZSHTN-xNN,x = 0.1, 0.15, 0.2, 0.25) ceramics were fabricated. The influence of co-doping of NN and high entropy perovskite oxide (SZSHTN) on the phase structure, microstructure and dielectric properties of NBT-based lead-free ceramics was investigated. Dense microstructure with a grain size of∼5μm is observed. Whenx = 0.25, a wide dielectric temperature stable range of − 35.4–224.3∘C with a low temperature coefficient of capacitance of 10% is achieved, fulfilling the industry standard of Y9P specification. Furthermore, excellent energy storage performance with recoverable energy density of 2.4 J/cm3, discharge efficiency of 71%, power density of 25.495 MW/cm3 and discharge rate 200 ns are simultaneously obtained, which shows great potential for high temperature capacitor applications.In this work, novel (1 − x)(0.75Na0.5Bi0.5TiO3)-0.25Sr(Zr0.2Sn0.2Hf0.2Ti0.2Nb0.2)O3-xNaNbO3 (NBT-SZSHTN-xNN,x = 0.1, 0.15, 0.2, 0.25) ceramics were fabricated. The influence of co-doping of NN and high entropy perovskite oxide (SZSHTN) on the phase structure, microstructure and dielectric properties of NBT-based lead-free ceramics was investigated. Dense microstructure with a grain size of∼5μm is observed. Whenx = 0.25, a wide dielectric temperature stable range of − 35.4–224.3∘C with a low temperature coefficient of capacitance of 10% is achieved, fulfilling the industry standard of Y9P specification. Furthermore, excellent energy storage performance with recoverable energy density of 2.4 J/cm3, discharge efficiency of 71%, power density of 25.495 MW/cm3 and discharge rate 200 ns are simultaneously obtained, which shows great potential for high temperature capacitor applications.

It is crucial to discover lead-free materials with ultrahigh recoverable energy density (Wrec) that can be employed in future pulse power capacitors. In this work, a highWrecof 4.51 J/cm3 was successfully obtained in lead-free Nd-doped AgNb0.8Ta0.2O3 antiferroelectric ceramics at an applied electric field of 290 kV/cm. It is discovered that Nd doping paired with Nb-site vacancies could stabilize the antiferroelectric phase by lowering the temperatures of the M1–M2 and M2–M3 phase transitions, which leads to higher energy storage efficiency. Furthermore, Nd and Ta co-doping will contribute to the electrical homogeneity and low electrical conductivity, resulting in large breakdown strengths. Aliovalent doping in Ag-site with Nb-site vacancies serves as a novel strategy for the construction of AgNbO3-based ceramics with excellent energy storage performance.It is crucial to discover lead-free materials with ultrahigh recoverable energy density (Wrec) that can be employed in future pulse power capacitors. In this work, a highWrecof 4.51 J/cm3 was successfully obtained in lead-free Nd-doped AgNb0.8Ta0.2O3 antiferroelectric ceramics at an applied electric field of 290 kV/cm. It is discovered that Nd doping paired with Nb-site vacancies could stabilize the antiferroelectric phase by lowering the temperatures of the M1–M2 and M2–M3 phase transitions, which leads to higher energy storage efficiency. Furthermore, Nd and Ta co-doping will contribute to the electrical homogeneity and low electrical conductivity, resulting in large breakdown strengths. Aliovalent doping in Ag-site with Nb-site vacancies serves as a novel strategy for the construction of AgNbO3-based ceramics with excellent energy storage performance.

Lead-free relaxor ceramics (1 − x)K0.5Na0.5NbO3 − xBi(Mn0.5Ni0.5)O3 ((1 − x )KNN-xBMN) with considerable charge–discharge characteristics and energy storage properties were prepared by a solid state method. Remarkable, a BMN doping level of 0.04, 0.96KNN–0.04BMN ceramic obtained good energy storage performance with acceptable energy storage densityWrec of 1.826 J/cm3 and energy storage efficiencyη of 77.4%, as well as good frequency stability (1–500 Hz) and fatigue resistance (1–5000 cycles). Meanwhile, a satisfactory charge–discharge performance with power densityPD∼ 98.90 MW/cm3, discharge timet0.9 ∘C) was obtained in 0.96KNN–0.04BMN ceramic. The small grain size (∼150 nm) and the high polarizability of Bi3+ are directly related to its good energy storage capacity. This work proposes a feasible approach for lead-free KNN-based ceramics to achieve high-energy storage and ultra-fast charge–discharge performance as well as candidate materials for the application of advanced high-temperature pulse capacitors.Lead-free relaxor ceramics (1 − x)K0.5Na0.5NbO3 − xBi(Mn0.5Ni0.5)O3 ((1 − x )KNN-xBMN) with considerable charge–discharge characteristics and energy storage properties were prepared by a solid state method. Remarkable, a BMN doping level of 0.04, 0.96KNN–0.04BMN ceramic obtained good energy storage performance with acceptable energy storage densityWrec of 1.826 J/cm3 and energy storage efficiencyη of 77.4%, as well as good frequency stability (1–500 Hz) and fatigue resistance (1–5000 cycles). Meanwhile, a satisfactory charge–discharge performance with power densityPD∼ 98.90 MW/cm3, discharge timet0.9 ∘C) was obtained in 0.96KNN–0.04BMN ceramic. The small grain size (∼150 nm) and the high polarizability of Bi3+ are directly related to its good energy storage capacity. This work proposes a feasible approach for lead-free KNN-based ceramics to achieve high-energy storage and ultra-fast charge–discharge performance as well as candidate materials for the application of advanced high-temperature pulse capacitors.

In this work, (1 − x)(0.92NaNbO3–0.08BaTiO3)–xCa0.7La0.2TiO3 (NNBT –xCLT) ceramics were successfully designed and prepared by the solid-state reaction method. Investigations on the structure, dielectric, and energy storage properties were performed. The NNBT – 0.25CLT ceramic with orthorhombic phase at room temperature was found to exhibit extremely small grain size and compacted microstructure. A largeWrec of 3.1 J/cm3 and a highη of 91.5% under the electric field of 360 kV/cm were achieved simultaneously in the sample. In addition, the energy storage performance of the sample exhibits thermal stability over the temperature range of 25–140∘C and the frequency range of 5–500 Hz. The charge and discharge tests reveal that the ceramic shows a large current densityCD of 965 A/cm2 and power densityPD of 154 MW/cm3. This work demonstrates that the NNBT–0.25CLT ceramic is a prospective energy storage material for potential application in the field of pulsed power devices.In this work, (1 − x)(0.92NaNbO3–0.08BaTiO3)–xCa0.7La0.2TiO3 (NNBT –xCLT) ceramics were successfully designed and prepared by the solid-state reaction method. Investigations on the structure, dielectric, and energy storage properties were performed. The NNBT – 0.25CLT ceramic with orthorhombic phase at room temperature was found to exhibit extremely small grain size and compacted microstructure. A largeWrec of 3.1 J/cm3 and a highη of 91.5% under the electric field of 360 kV/cm were achieved simultaneously in the sample. In addition, the energy storage performance of the sample exhibits thermal stability over the temperature range of 25–140∘C and the frequency range of 5–500 Hz. The charge and discharge tests reveal that the ceramic shows a large current densityCD of 965 A/cm2 and power densityPD of 154 MW/cm3. This work demonstrates that the NNBT–0.25CLT ceramic is a prospective energy storage material for potential application in the field of pulsed power devices.

Ferroelectric materials are considered to be the most competitive energy storage materials for applications in pulsed power electronics due to excellent charge–discharge properties. However, the low energy storage density is the primary problem limiting their practical application. In this study, (1 − x)Na0.5Bi0.5TiO3 – xSr0.7La0.2TiO3[(1 − x)NBT–xSLT] ferroelectric ceramics are found to exhibit excellent energy storage performances through a synergistic strategy. As the SLT concentration increases, the relaxation characteristic increases significantly and the breakdown strength increases dramatically from 150 kV/cm to 220 kV/cm. The recoverable energy storage density of the 0.55NBT–0.45SLT ceramic is 2.86 J/cm3 with an energy storage efficiency of 88% under an electric field of 220 kV/cm. Furthermore, the ceramic withx = 0.45 mol exhibited excellent energy storage stability in the ranges of 20–180∘C (temperature) and 1–125 Hz (frequency). These excellent properties demonstrate the potential of (1 − x)NBT–xSLT ceramics when used as dielectric capacitors in pulsed power systems.Ferroelectric materials are considered to be the most competitive energy storage materials for applications in pulsed power electronics due to excellent charge–discharge properties. However, the low energy storage density is the primary problem limiting their practical application. In this study, (1 − x)Na0.5Bi0.5TiO3 – xSr0.7La0.2TiO3[(1 − x)NBT–xSLT] ferroelectric ceramics are found to exhibit excellent energy storage performances through a synergistic strategy. As the SLT concentration increases, the relaxation characteristic increases significantly and the breakdown strength increases dramatically from 150 kV/cm to 220 kV/cm. The recoverable energy storage density of the 0.55NBT–0.45SLT ceramic is 2.86 J/cm3 with an energy storage efficiency of 88% under an electric field of 220 kV/cm. Furthermore, the ceramic withx = 0.45 mol exhibited excellent energy storage stability in the ranges of 20–180∘C (temperature) and 1–125 Hz (frequency). These excellent properties demonstrate the potential of (1 − x)NBT–xSLT ceramics when used as dielectric capacitors in pulsed power systems.

Dielectric polymer film capacitors with a high-power density as well as efficient charge and discharge rates have great potential for application to fulfill the miniaturized and lightweight requirements of the electronic and stationary power systems. It was reported that the elastic recovery rate and energy storage density of poly (vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] polymer film can be enhanced through thermostatic uniaxial stretching. But it is unknown about the relationship between the stretching rate and above properties. In this study, we investigated the effect of different stretching rates on the conformation, elastic recovery, dielectric constant, and energy storage density of stretched P(VDF-CTFE) polymer films. It was found that the stretching rate significantly affected the formation of polarβ-crystal phase, causing different dielectric properties. The degrees of elastic recovery of P(VDF-CTFE) film vary with stretching rates. Among them, the elastic recovery rate of the P(VDF-CTFE) 94/6 film is 46.5% at a stretching rate of 15 mm/min, the dielectric constant is 12.25 at 100 Hz, and the energy density reaches 3.95 J/cm3 with the energy loss of 39% at 200 MV/m field.Dielectric polymer film capacitors with a high-power density as well as efficient charge and discharge rates have great potential for application to fulfill the miniaturized and lightweight requirements of the electronic and stationary power systems. It was reported that the elastic recovery rate and energy storage density of poly (vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] polymer film can be enhanced through thermostatic uniaxial stretching. But it is unknown about the relationship between the stretching rate and above properties. In this study, we investigated the effect of different stretching rates on the conformation, elastic recovery, dielectric constant, and energy storage density of stretched P(VDF-CTFE) polymer films. It was found that the stretching rate significantly affected the formation of polarβ-crystal phase, causing different dielectric properties. The degrees of elastic recovery of P(VDF-CTFE) film vary with stretching rates. Among them, the elastic recovery rate of the P(VDF-CTFE) 94/6 film is 46.5% at a stretching rate of 15 mm/min, the dielectric constant is 12.25 at 100 Hz, and the energy density reaches 3.95 J/cm3 with the energy loss of 39% at 200 MV/m field.

With the increasing demand of high-power and pulsed power electronic devices, environmental-friendly potassium sodium niobate ((Na0.5K0.5)NbO3, KNN) ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density (Wrec). Nevertheless, the dielectric loss also increases as the external electric field increases, which will generate much dissipated energy and raise the temperature of ceramic capacitors. Thus, an effective strategy is proposed to enhance the energy storage efficiency (η) via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na0.5K0.5)-NbO3–0.1Bi(Zn2/3(NbxTa1−x)1/3)O3 ceramics. On the one hand, the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short–range polar nanoregions (PNRs), resulting in the highη. On the other hand, the introduction of Ta ions could boost the intrinsic band energy gap and thus improve theEb. As a result, highWrec of 3.29 J/cm3 and ultrahighη of 90.1% at the high external electric field of 310 kV/cm are achieved inx = 0.5 sample. These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.With the increasing demand of high-power and pulsed power electronic devices, environmental-friendly potassium sodium niobate ((Na0.5K0.5)NbO3, KNN) ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density (Wrec). Nevertheless, the dielectric loss also increases as the external electric field increases, which will generate much dissipated energy and raise the temperature of ceramic capacitors. Thus, an effective strategy is proposed to enhance the energy storage efficiency (η) via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na0.5K0.5)-NbO3–0.1Bi(Zn2/3(NbxTa1−x)1/3)O3 ceramics. On the one hand, the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short–range polar nanoregions (PNRs), resulting in the highη. On the other hand, the introduction of Ta ions could boost the intrinsic band energy gap and thus improve theEb. As a result, highWrec of 3.29 J/cm3 and ultrahighη of 90.1% at the high external electric field of 310 kV/cm are achieved inx = 0.5 sample. These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.

In this work, we show that a d33～150 pC/N can be obtained in nonpoled poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) copolymer films with an arch structure. The copolymer films, which are often thought to be homogeneous, are in fact inhomogeneous in microstructure and physical properties after film fabrication. Although a large proportion of the copolymer film is nonpolar, as expected in a nonpoled ferroelectric film, the surface regions of the film are spontaneously polarized. We propose that inhomogeneous stress in the surface regions, which is either from the constraint of the substrate or skin layer effect formed during the film fabrication, generates a flexoelectric response and orients the spontaneous polarization of the ferroelectric film. As a result of the polar surface regions, the nonpoled films exhibit a piezoelectric response. The piezoelectric response is further amplified by the special arch structure of the films, leading to the observed large effective piezoelectric response. This study not only discovers the polar surface effect in ferroelectric polymer films, but also proposes an approach to design polymer materials with a strong piezoelectric response.In this work, we show that a d33～150 pC/N can be obtained in nonpoled poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) copolymer films with an arch structure. The copolymer films, which are often thought to be homogeneous, are in fact inhomogeneous in microstructure and physical properties after film fabrication. Although a large proportion of the copolymer film is nonpolar, as expected in a nonpoled ferroelectric film, the surface regions of the film are spontaneously polarized. We propose that inhomogeneous stress in the surface regions, which is either from the constraint of the substrate or skin layer effect formed during the film fabrication, generates a flexoelectric response and orients the spontaneous polarization of the ferroelectric film. As a result of the polar surface regions, the nonpoled films exhibit a piezoelectric response. The piezoelectric response is further amplified by the special arch structure of the films, leading to the observed large effective piezoelectric response. This study not only discovers the polar surface effect in ferroelectric polymer films, but also proposes an approach to design polymer materials with a strong piezoelectric response.

BiScO3–PbTiO3 binary ceramics own both high Curie temperature and prominent piezoelectric properties, while the high dielectric loss needs to be reduced substantially for practical application especially at high temperatures. In this work, a ternary perovskite system of (1–x–y)BiScO3–yPbTiO3–xBi(Mn2/3Sb1/3)O3 (BS–yPT–xBMS) with x = 0.005, y = 0.630–0.645 and x = 0.015, y = 0.625–0.640 was prepared by the traditional solid-state reaction method. The phase structure, microstructure, dielectric/piezoelectric/ferroelectric properties were studied. Among BS–yPT–xBMS ceramic series, the BS–0.630PT–0.015BMS at morphotropic phase boundary possesses the reduced dielectric loss factor (tanδ = 1.20%) and increased mechanical quality factor (Qm = 84), and maintains a high Curie temperature ( TC = 410°C) and excellent piezoelectric properties (d33 = 330 pC/N) simultaneously. Of particular importance, at elevated temperature of 200°C, the value of tanδ is only increased to 1.59%. All these properties indicate that the BS–0.630PT–0.015BMS ceramic has great potential for application in high-temperature piezoelectric devices.BiScO3–PbTiO3 binary ceramics own both high Curie temperature and prominent piezoelectric properties, while the high dielectric loss needs to be reduced substantially for practical application especially at high temperatures. In this work, a ternary perovskite system of (1–x–y)BiScO3–yPbTiO3–xBi(Mn2/3Sb1/3)O3 (BS–yPT–xBMS) with x = 0.005, y = 0.630–0.645 and x = 0.015, y = 0.625–0.640 was prepared by the traditional solid-state reaction method. The phase structure, microstructure, dielectric/piezoelectric/ferroelectric properties were studied. Among BS–yPT–xBMS ceramic series, the BS–0.630PT–0.015BMS at morphotropic phase boundary possesses the reduced dielectric loss factor (tanδ = 1.20%) and increased mechanical quality factor (Qm = 84), and maintains a high Curie temperature ( TC = 410°C) and excellent piezoelectric properties (d33 = 330 pC/N) simultaneously. Of particular importance, at elevated temperature of 200°C, the value of tanδ is only increased to 1.59%. All these properties indicate that the BS–0.630PT–0.015BMS ceramic has great potential for application in high-temperature piezoelectric devices.

The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 μm-thick Bi(Fe0.93Mn0.05Ti0.02)O3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 μC/cm2, and a remanent polarization of 70 μC/cm2. Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field (P?E) loops with a positive shift along the x-axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of P?E loops on frequency (1–50 kHz) and temperature (25–125°C) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems.The BiFeO3-based film is one of the most promising candidates for lead-free piezoelectric film devices. In this work, the 1 μm-thick Bi(Fe0.93Mn0.05Ti0.02)O3 (BFMT) films are grown on the ITO/glass substrate using a sol-gel method combined with spin-coating and layer-by-layer annealing technique. These films display a large saturated polarization of 95 μC/cm2, and a remanent polarization of 70 μC/cm2. Especially, the films are self-poled caused by an internal bias field, giving rise to asymmetric polarization-electric field (P?E) loops with a positive shift along the x-axis. A stable self-polarization state is maintained during the applied electric field increasing to 1500 kV/cm and then decreasing back. The weak dependence of P?E loops on frequency (1–50 kHz) and temperature (25–125°C) indicate that the internal bias field can be stable within a certain frequency and temperature range. These results demonstrate that the self-polarized BFMT thick films can be integrated into devices without any poling process, with promising applications in micro-electro-mechanical systems.

To improve the acoustic radiation performance of the spherical transducer, a prestressed layer is formed in the transducer through fiber winding. The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress (Tr) and acoustic impedance, respectively. First, a theoretical estimation of Tr is established with a thin shell approximation of the prestressed layer. Then, the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer. Further, the ideal effects of Tr on the sound radiation performances of the transducer are analyzed through finite element analysis (FEA). Finally, four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer. The results show that with the growth of Tr, the acoustic impedance of the prestressed layer grows, mitigating the enormous impedance mismatch between the piezoelectric ceramic and water, while increasing attenuation of the acoustic energy, resulting in a peak value of the maximum transmitting voltage response (TVRmax) at 1.18 MPa. The maximum drive voltage increases with Tr, leading to a steady growth of the maximum transmitting sound level (SLmax), with a noticeable ascend of 3.9 dB at a 3.44 MPa Tr. This is a strong credibility that the prestressed layer could improve the sound radiation performance of the spherical transducer.To improve the acoustic radiation performance of the spherical transducer, a prestressed layer is formed in the transducer through fiber winding. The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress (Tr) and acoustic impedance, respectively. First, a theoretical estimation of Tr is established with a thin shell approximation of the prestressed layer. Then, the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer. Further, the ideal effects of Tr on the sound radiation performances of the transducer are analyzed through finite element analysis (FEA). Finally, four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer. The results show that with the growth of Tr, the acoustic impedance of the prestressed layer grows, mitigating the enormous impedance mismatch between the piezoelectric ceramic and water, while increasing attenuation of the acoustic energy, resulting in a peak value of the maximum transmitting voltage response (TVRmax) at 1.18 MPa. The maximum drive voltage increases with Tr, leading to a steady growth of the maximum transmitting sound level (SLmax), with a noticeable ascend of 3.9 dB at a 3.44 MPa Tr. This is a strong credibility that the prestressed layer could improve the sound radiation performance of the spherical transducer.

In this work, Li2CO3 was added into 0.7BiFeO3?0.3BaZr0.02Ti0.98O3?0.01molMnO2 (70BFBTMn) piezoelectric ceramics to reduce their sintering temperatures. 70BFBTMn ceramics were sintered by a conventional solid reaction method, and their structural, dielectric, piezoelectric and ferroelectric properties were studied. These results indicate that 0.5% (mole) Li2CO3 is the optimized content and it can reduce the sintering temperature by 100°C, making the possibility of the piezoelectric ceramics cofiring with Ag electrodes at low temperatures to manufacture multilayer piezoelectric actuators.In this work, Li2CO3 was added into 0.7BiFeO3?0.3BaZr0.02Ti0.98O3?0.01molMnO2 (70BFBTMn) piezoelectric ceramics to reduce their sintering temperatures. 70BFBTMn ceramics were sintered by a conventional solid reaction method, and their structural, dielectric, piezoelectric and ferroelectric properties were studied. These results indicate that 0.5% (mole) Li2CO3 is the optimized content and it can reduce the sintering temperature by 100°C, making the possibility of the piezoelectric ceramics cofiring with Ag electrodes at low temperatures to manufacture multilayer piezoelectric actuators.

Relaxor-based ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals and ceramics are promising candidates for high-performance electromechanical conversion devices. It is known that the domain structure and dielectric diffusion–relaxation characteristics are crucial to the excellent performances of relaxor ferroelectrics. In this work, we prepared the PIN–PMN–PT ceramics with various PIN/PMN proportions and systematically investigated their domain structure and dielectric diffusion–relaxation properties. The effect of PIN/PMN proportion on the domain size and dielectric diffusion–relaxation characteristics was also studied. The investigations showed that PIN–PMN–PT ceramics presented multi-type domain patterns comprising irregular island domains and regular lamellar domains. Moreover, the dependent relations of PIN/PMN proportions on the dielectric diffusion and domain size indicated that the PIN composition has a stronger lattice distortion than PMN composition; increasing the PIN proportion can enhance the dielectric diffusion and decrease the domain size. Our results could deepen the understanding of structure–property relationships of multicomponent relaxor ferroelectrics and guide the design and exploration of new high-performance ferroelectric materials.Relaxor-based ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) single crystals and ceramics are promising candidates for high-performance electromechanical conversion devices. It is known that the domain structure and dielectric diffusion–relaxation characteristics are crucial to the excellent performances of relaxor ferroelectrics. In this work, we prepared the PIN–PMN–PT ceramics with various PIN/PMN proportions and systematically investigated their domain structure and dielectric diffusion–relaxation properties. The effect of PIN/PMN proportion on the domain size and dielectric diffusion–relaxation characteristics was also studied. The investigations showed that PIN–PMN–PT ceramics presented multi-type domain patterns comprising irregular island domains and regular lamellar domains. Moreover, the dependent relations of PIN/PMN proportions on the dielectric diffusion and domain size indicated that the PIN composition has a stronger lattice distortion than PMN composition; increasing the PIN proportion can enhance the dielectric diffusion and decrease the domain size. Our results could deepen the understanding of structure–property relationships of multicomponent relaxor ferroelectrics and guide the design and exploration of new high-performance ferroelectric materials.

Recent studies have shown that nitrogen doping of carbon nanotubes (CNTs) can lead to the formation of piezoelectric properties in them, not characteristic of pure CNTs. In this work, nitrogen-doped CNTs were grown by plasma-enhanced chemical vapor deposition and the effect of the aspect ratio of the nanotube length to its diameter on its piezoelectric coefficient d33 was shown. It was observed that as the aspect ratio of the nanotube increased from 7 to 21, the value of d33 increased linearly from 7.3 to 10.7 pm/V. This dependence is presumably due to an increase in curvature-induced polarization because of an increase in the curvature and the number of bamboo-like “bridges” in the nanotube cavity formed as a result of the incorporation of pyrrole-like nitrogen into the nanotube structure. The obtained results can be used in the development of promising elements of nanopiezotronics (nanogenerators, memory elements, and strain sensors).Recent studies have shown that nitrogen doping of carbon nanotubes (CNTs) can lead to the formation of piezoelectric properties in them, not characteristic of pure CNTs. In this work, nitrogen-doped CNTs were grown by plasma-enhanced chemical vapor deposition and the effect of the aspect ratio of the nanotube length to its diameter on its piezoelectric coefficient d33 was shown. It was observed that as the aspect ratio of the nanotube increased from 7 to 21, the value of d33 increased linearly from 7.3 to 10.7 pm/V. This dependence is presumably due to an increase in curvature-induced polarization because of an increase in the curvature and the number of bamboo-like “bridges” in the nanotube cavity formed as a result of the incorporation of pyrrole-like nitrogen into the nanotube structure. The obtained results can be used in the development of promising elements of nanopiezotronics (nanogenerators, memory elements, and strain sensors).

The present investigations mainly focused on the colossal dielectric response and complex impedance analysis of LaFeO3 ceramics. The studied sample was prepared by a citrate gel method. Structural and microstructural properties are analyzed from the XRD pattern and SEM micrograph. The anomalies in the dielectric constant versus temperature plots are analyzed on the basis of polarization induced by the Maxwell-Wagner mechanisms and ferromagnetic interaction between the Fe3+ ions driven by the oxygen vacancy mediated Fe3+–Vo –Fe3+ exchange interaction A giant dielectric permittivity in the order of ∼105 was observed in the sample even at the room temperature for 100 Hz. The colossal dielectric constant in LaFeO3 is mainly driven by the internal barrier layer capacitor (IBLC) formation. The formation of IBLC was explained on the basis of highly insulating grain boundary and less resistive/semiconducting grain, which was confirmed from both the resistance and capacitance of grain and grain boundary from the impedance analysis. The non-Debye-type relaxation process associated with the grain and grain boundary effect was investigated from the broad and asymmetric relaxation peak. The relaxation time for both the grain and grain boundary effect was also calculated. In addition to this, we have also analyzed the normalized bode plot of imaginary part of impedance and electrical modulus which suggests the relaxation process dominated by the short-range movement of charge carriers.The present investigations mainly focused on the colossal dielectric response and complex impedance analysis of LaFeO3 ceramics. The studied sample was prepared by a citrate gel method. Structural and microstructural properties are analyzed from the XRD pattern and SEM micrograph. The anomalies in the dielectric constant versus temperature plots are analyzed on the basis of polarization induced by the Maxwell-Wagner mechanisms and ferromagnetic interaction between the Fe3+ ions driven by the oxygen vacancy mediated Fe3+–Vo –Fe3+ exchange interaction A giant dielectric permittivity in the order of ∼105 was observed in the sample even at the room temperature for 100 Hz. The colossal dielectric constant in LaFeO3 is mainly driven by the internal barrier layer capacitor (IBLC) formation. The formation of IBLC was explained on the basis of highly insulating grain boundary and less resistive/semiconducting grain, which was confirmed from both the resistance and capacitance of grain and grain boundary from the impedance analysis. The non-Debye-type relaxation process associated with the grain and grain boundary effect was investigated from the broad and asymmetric relaxation peak. The relaxation time for both the grain and grain boundary effect was also calculated. In addition to this, we have also analyzed the normalized bode plot of imaginary part of impedance and electrical modulus which suggests the relaxation process dominated by the short-range movement of charge carriers.

Epitaxial VO2 films grown by pulsed laser deposition (PLD) method with superior phase transition related switching characteristics are successfully embedded to SAW devices using concept of the “impedance loaded SAW sensor”. A resistance of VO2 sensor abruptly drops from 0.7 MΩ to 90 Ω when it is heated above ∼65∘C and shows a narrow hysteresis loops when switching. Two designs of SAW devices are examined in which RF signal is reflected back from interdigital transducer (IDT) or a surface acoustic waves (SAW) is transferred through a coupler and the RF response is altered 2 and 3 times correspondingly upon the phase transition in VO2. In the proposed devices with external load, a SAW does not propagate via VO2 film and therefore is not attenuated which is beneficiary for wireless applications. Additionally, a SAW phase shift as great as 50∘ is induced to the SAW transferred through the coupler due to the phase transition in VO2. The proposed approach may boost the development of remotely controlled autonomous sensors, including those based on VO2 metamaterials and hybrid plasmonic structures for near IR/middle IR and sub-THz/THz applications.Epitaxial VO2 films grown by pulsed laser deposition (PLD) method with superior phase transition related switching characteristics are successfully embedded to SAW devices using concept of the “impedance loaded SAW sensor”. A resistance of VO2 sensor abruptly drops from 0.7 MΩ to 90 Ω when it is heated above ∼65∘C and shows a narrow hysteresis loops when switching. Two designs of SAW devices are examined in which RF signal is reflected back from interdigital transducer (IDT) or a surface acoustic waves (SAW) is transferred through a coupler and the RF response is altered 2 and 3 times correspondingly upon the phase transition in VO2. In the proposed devices with external load, a SAW does not propagate via VO2 film and therefore is not attenuated which is beneficiary for wireless applications. Additionally, a SAW phase shift as great as 50∘ is induced to the SAW transferred through the coupler due to the phase transition in VO2. The proposed approach may boost the development of remotely controlled autonomous sensors, including those based on VO2 metamaterials and hybrid plasmonic structures for near IR/middle IR and sub-THz/THz applications.

A method for obtaining a new type of surface acoustic wave (SAW) transducer operating at double frequency with a single-phase closed-loop lattice and a piezoelectric zinc oxide film is developed and experimentally investigated. A method for calculating such a transducer has been developed, its equivalent circuit has been compiled, taking into account propagation losses, losses in the metal film and the inductance of the connecting wires. When the frequency is doubled, the SAW attenuation per unit length increases.A method for obtaining a new type of surface acoustic wave (SAW) transducer operating at double frequency with a single-phase closed-loop lattice and a piezoelectric zinc oxide film is developed and experimentally investigated. A method for calculating such a transducer has been developed, its equivalent circuit has been compiled, taking into account propagation losses, losses in the metal film and the inductance of the connecting wires. When the frequency is doubled, the SAW attenuation per unit length increases.

To solve the problem of directional arrangement of small template particles, we designed a lamination technique for the preparation of dense ceramics with high texture degree based on the phase-field simulation. Referring to the experimental data, the initial microstructures of the template and matrix layers were constructed. The effect of the average length of template on the coarsening behavior of the template layer was investigated in detail. The results suggested that there was a stable stage in the growth process of template grains, which would be conducive to the densification of textured ceramics. This phenomenon has been confirmed by corresponding experiments. In addition, we demonstrated a critical thickness of matrix layer for the preparation of highly textured ceramics by using the template with various average lengths. The grain size of highly textured ceramics could be controlled by adjusting the template size and thickness of matrix layer.To solve the problem of directional arrangement of small template particles, we designed a lamination technique for the preparation of dense ceramics with high texture degree based on the phase-field simulation. Referring to the experimental data, the initial microstructures of the template and matrix layers were constructed. The effect of the average length of template on the coarsening behavior of the template layer was investigated in detail. The results suggested that there was a stable stage in the growth process of template grains, which would be conducive to the densification of textured ceramics. This phenomenon has been confirmed by corresponding experiments. In addition, we demonstrated a critical thickness of matrix layer for the preparation of highly textured ceramics by using the template with various average lengths. The grain size of highly textured ceramics could be controlled by adjusting the template size and thickness of matrix layer.

The (1−x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO 3)–xKTaO3(BNBT–xKT) lead-free ferroelectric ceramics were produced using the traditional solid-state sintering technique, and the phase structure, surface morphology, electrical properties were all thoroughly examined. Every ceramic has a single perovskite structure and there is no second phase, as shown by the XRD patterns and Raman spectra. Scanning electron microscopy revealed that all samples displayed dense microstructure and cubic grain. In addition, KT encourages grain growth due to the oxygen vacancies induced by doping or volatilization of ions at high temperatures. The Tmof the ceramics decreases with increasing doping levels due to oxygen vacancies acting as dipoles upon the addition of KT, and the dielectric loss of all samples is low at ambient temperature. In comparison to the pure BNBT ceramic’s bipolar strain value of 0.12%, the BNBT–2KT ceramic achieved a maximum bipolar strain of ∼0.506% and unipolar strain of ∼ 0.430% with the corresponding d33*up to 538 pm/V under 80 kV/cm field. Performance significantly improved as a result of this. A test of the correlation between temperature and ferroelectric properties shows that the largest strain value of the BNBT–2KT ceramic occurs at ambient temperature and that the phase change from ferroelectric to relaxor is complete. Additionally, it is discovered that the BNBT–3KT ceramic can sustain a stable strain across a broad temperature range, suggesting that it has good temperature stability. The aforementioned findings demonstrate that lead-based ceramics may be replaced with BNBT–xKT ceramics.The (1−x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO 3)–xKTaO3(BNBT–xKT) lead-free ferroelectric ceramics were produced using the traditional solid-state sintering technique, and the phase structure, surface morphology, electrical properties were all thoroughly examined. Every ceramic has a single perovskite structure and there is no second phase, as shown by the XRD patterns and Raman spectra. Scanning electron microscopy revealed that all samples displayed dense microstructure and cubic grain. In addition, KT encourages grain growth due to the oxygen vacancies induced by doping or volatilization of ions at high temperatures. The Tmof the ceramics decreases with increasing doping levels due to oxygen vacancies acting as dipoles upon the addition of KT, and the dielectric loss of all samples is low at ambient temperature. In comparison to the pure BNBT ceramic’s bipolar strain value of 0.12%, the BNBT–2KT ceramic achieved a maximum bipolar strain of ∼0.506% and unipolar strain of ∼ 0.430% with the corresponding d33*up to 538 pm/V under 80 kV/cm field. Performance significantly improved as a result of this. A test of the correlation between temperature and ferroelectric properties shows that the largest strain value of the BNBT–2KT ceramic occurs at ambient temperature and that the phase change from ferroelectric to relaxor is complete. Additionally, it is discovered that the BNBT–3KT ceramic can sustain a stable strain across a broad temperature range, suggesting that it has good temperature stability. The aforementioned findings demonstrate that lead-based ceramics may be replaced with BNBT–xKT ceramics.

This work promotes the room temperature energy storage properties of the multiferroics. In this approach, impacts of PrFeO3 doping on PT-based solid solutions (Pb1−xPrxTi1−xFexO3, x = 0.21, 0.22, 0.23, 0.24, 0.25 and 0.26) have been explored. X-ray diffraction (XRD) patterns were used to estimate the crystallographic parameters, confirming the single phase tetragonal structure. The ferroelectric Curie temperature (TcFE) is observed to drop from 410 K to below room temperature as the Pr concentration increases. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The sample x = 0.24 achieved the maximum value of energy storage density of 362.25 mJ/cm3 with the efficiency of 40.5%. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The validity of magnetoelectric coupling in all samples was confirmed by magneto-dielectric studies and found that the sample x = 0.24 shows the maximum response with the coupling coefficient (γ) = 15.54 g2/emu2.This work promotes the room temperature energy storage properties of the multiferroics. In this approach, impacts of PrFeO3 doping on PT-based solid solutions (Pb1−xPrxTi1−xFexO3, x = 0.21, 0.22, 0.23, 0.24, 0.25 and 0.26) have been explored. X-ray diffraction (XRD) patterns were used to estimate the crystallographic parameters, confirming the single phase tetragonal structure. The ferroelectric Curie temperature (TcFE) is observed to drop from 410 K to below room temperature as the Pr concentration increases. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The sample x = 0.24 achieved the maximum value of energy storage density of 362.25 mJ/cm3 with the efficiency of 40.5%. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The validity of magnetoelectric coupling in all samples was confirmed by magneto-dielectric studies and found that the sample x = 0.24 shows the maximum response with the coupling coefficient (γ) = 15.54 g2/emu2.

Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics, the limitation of weak piezoelectric response and their temperature sensitivity to applications is worth exploring. Herein, the textured (1-x)(K0.5Na0.5)(Nb0.96Sb0.04)O3-x(Bi0.5Na0.5)HfO3(x = 0.01−0.045) lead-free ceramics were synthesized by templated grain-growth method. The high piezoelectric performance (d33 of 474 pC/N and strain of 0.21%) and excellent temperature stability (unipolar strain maintained within 4.3% change between 30∘C and 165∘C) were simultaneously achieved in the textured KNNS-0.03BNH ceramics. The high piezoelectric performance can be attributed to the summation of the crystallographic anisotropy and phase structure contributions in textured ceramics. The superior temperature stability of piezoelectric properties can be interpreted by the contribution of crystal anisotropy to piezoelectric properties reduces the effect of phase transition on piezoelectric properties deterioration. This study provides an effective strategy for simultaneously achieving high piezoelectric properties and superior temperature stability in KNN-based textured ceramics.Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics, the limitation of weak piezoelectric response and their temperature sensitivity to applications is worth exploring. Herein, the textured (1-x)(K0.5Na0.5)(Nb0.96Sb0.04)O3-x(Bi0.5Na0.5)HfO3(x = 0.01−0.045) lead-free ceramics were synthesized by templated grain-growth method. The high piezoelectric performance (d33 of 474 pC/N and strain of 0.21%) and excellent temperature stability (unipolar strain maintained within 4.3% change between 30∘C and 165∘C) were simultaneously achieved in the textured KNNS-0.03BNH ceramics. The high piezoelectric performance can be attributed to the summation of the crystallographic anisotropy and phase structure contributions in textured ceramics. The superior temperature stability of piezoelectric properties can be interpreted by the contribution of crystal anisotropy to piezoelectric properties reduces the effect of phase transition on piezoelectric properties deterioration. This study provides an effective strategy for simultaneously achieving high piezoelectric properties and superior temperature stability in KNN-based textured ceramics.

Solid solution samples of the three-component system (1 − x)Pb(Ti0.5Zr0.5)O3−xCdNb2O6 with x = 0.0125–0.0500, Δx = 0.0125 were obtained by solid phase synthesis followed by sintering using conventional ceramic technology. The crystal structure, microstructure, electrophysical, and thermophysical properties of these ceramics have been studied. It is shown that all studied solid solutions can be divided into two groups (with x = 0.0125 and with x> 0.0125), characterized by different characteristics of the change in properties with variations in external influences. This is probably due to the transition from a perovskite-type structure with a tetragonal (T) unit cell to inhomogeneous solid solutions consisting of a series of T-phases with similar cell parameters. A conclusion is made about the expediency of using the data obtained in the development of similar materials for devices based on them.Solid solution samples of the three-component system (1 − x)Pb(Ti0.5Zr0.5)O3−xCdNb2O6 with x = 0.0125–0.0500, Δx = 0.0125 were obtained by solid phase synthesis followed by sintering using conventional ceramic technology. The crystal structure, microstructure, electrophysical, and thermophysical properties of these ceramics have been studied. It is shown that all studied solid solutions can be divided into two groups (with x = 0.0125 and with x> 0.0125), characterized by different characteristics of the change in properties with variations in external influences. This is probably due to the transition from a perovskite-type structure with a tetragonal (T) unit cell to inhomogeneous solid solutions consisting of a series of T-phases with similar cell parameters. A conclusion is made about the expediency of using the data obtained in the development of similar materials for devices based on them.

Dielectric properties and structure of pure and carbon-modified nanocomposites on the base of porous glasses with an average pore diameter of 6 nm (PG6) with embedded KNO3 have been studied at the temperature diapason of 300–430 K and at frequencies of 0.1–3 × 106 Hz on cooling. X-ray diffraction studies of these samples have shown, that in modified and unmodified composites there is a mixture of the low-temperature paraelectric phase (α-phase) and the ferroelectric γ-phase. In modified composites, a decrease in permittivity and conductivity is observed. Dielectric response has been analyzed in the framework of modern theoretical models. Two relaxation processes have been identified and their origin has been determined. It has been found that the main contribution to the dielectric response of nanocomposite material PG6+KNO3 is provided by charge polarization on interfaces, which can be governed by modifying the inner pore surfaces. DC-conductivity of both composites has been estimated and the activation energies have been determined. Activation energy change observed in a vicinity of 360 K is attributed to the phase transformation and the appearance of KNO3α-phase.Dielectric properties and structure of pure and carbon-modified nanocomposites on the base of porous glasses with an average pore diameter of 6 nm (PG6) with embedded KNO3 have been studied at the temperature diapason of 300–430 K and at frequencies of 0.1–3 × 106 Hz on cooling. X-ray diffraction studies of these samples have shown, that in modified and unmodified composites there is a mixture of the low-temperature paraelectric phase (α-phase) and the ferroelectric γ-phase. In modified composites, a decrease in permittivity and conductivity is observed. Dielectric response has been analyzed in the framework of modern theoretical models. Two relaxation processes have been identified and their origin has been determined. It has been found that the main contribution to the dielectric response of nanocomposite material PG6+KNO3 is provided by charge polarization on interfaces, which can be governed by modifying the inner pore surfaces. DC-conductivity of both composites has been estimated and the activation energies have been determined. Activation energy change observed in a vicinity of 360 K is attributed to the phase transformation and the appearance of KNO3α-phase.

This paper presents a theoretical model for describing the thermodynamic properties of doped ferroelectric crystals based on a modified Weiss mean-field approach. Accounting for quadrupole and octupole terms in the expression for the effective field within the Weiss model makes it possible to move from the Langevin equation to the Landau–Ginzburg equation. Furthermore, the coefficients of the Landau–Ginzburg equation can be expressed in terms of the physical parameters of the crystal lattice. For these parameters, analytical expressions are proposed that describe their change when adding dopants in ceramic matrix composites. Perovskite barium titanate ceramics with a variety of inclusions is considered as an application example of the developed method. The obtained agreement between the analytical and experimental results for barium titanate ceramics with lanthanum/magnesium/zirconium dopants gives us hope of the applicability of the present theory to the calculation of other doped ferroelectrics as well.This paper presents a theoretical model for describing the thermodynamic properties of doped ferroelectric crystals based on a modified Weiss mean-field approach. Accounting for quadrupole and octupole terms in the expression for the effective field within the Weiss model makes it possible to move from the Langevin equation to the Landau–Ginzburg equation. Furthermore, the coefficients of the Landau–Ginzburg equation can be expressed in terms of the physical parameters of the crystal lattice. For these parameters, analytical expressions are proposed that describe their change when adding dopants in ceramic matrix composites. Perovskite barium titanate ceramics with a variety of inclusions is considered as an application example of the developed method. The obtained agreement between the analytical and experimental results for barium titanate ceramics with lanthanum/magnesium/zirconium dopants gives us hope of the applicability of the present theory to the calculation of other doped ferroelectrics as well.

Domain pattern is the carrier of electromechanical property. A novel domain pattern will open a gate for ferroelectric nanodevice. A distinctive topological domain pattern termed as hierarchical vortex (Hvo) has been found in polycrystalline ferroelectric based on the first-principles-based atomistic method. The Hvo pattern displays a unique structure, which is a flux-closing vortex encircle an anti-vortex or a vortex and anti-vortex pair (VA). Each Hvo structure could be regarded as a single vortex to forming a vortex–anti-vortex pair with anti-vortex or forming a vortex–vortex array with the vortex. The mechanism of HVo obtained in polycrystalline ferroelectric has been found that the grain boundary (GB) equals the domain wall when the first-order vortex is in the vortex. The HVo will open a new view of the domain topology pattern and its evolution.Domain pattern is the carrier of electromechanical property. A novel domain pattern will open a gate for ferroelectric nanodevice. A distinctive topological domain pattern termed as hierarchical vortex (Hvo) has been found in polycrystalline ferroelectric based on the first-principles-based atomistic method. The Hvo pattern displays a unique structure, which is a flux-closing vortex encircle an anti-vortex or a vortex and anti-vortex pair (VA). Each Hvo structure could be regarded as a single vortex to forming a vortex–anti-vortex pair with anti-vortex or forming a vortex–vortex array with the vortex. The mechanism of HVo obtained in polycrystalline ferroelectric has been found that the grain boundary (GB) equals the domain wall when the first-order vortex is in the vortex. The HVo will open a new view of the domain topology pattern and its evolution.

This paper is devoted to a comprehensive study on a new type of microwave structures named magnetoelectric (ME) gradient structures. These structures are studied in this paper to understand the possibilities and application principles in feasible devices. The structure under study was calculated at different values of the applied electric field and different values of the relative permittivity of the artificial dielectric layer. The layered multiferroic structure in inhomogeneous electric and magnetic fields was calculated on the basis of the previously proposed mathematical model. The eigenwaves spectrum for several considered cases was the result of the performed calculation. The concept of using ME gradient structures in the design of electronically controlled microwave devices is formed on the basis of the results of a numerical experiment. Structures of this type will preferably be used in electronically controlled devices for the directional transmission of microwave signals, as it was shown in the theoretical part of the paper.This paper is devoted to a comprehensive study on a new type of microwave structures named magnetoelectric (ME) gradient structures. These structures are studied in this paper to understand the possibilities and application principles in feasible devices. The structure under study was calculated at different values of the applied electric field and different values of the relative permittivity of the artificial dielectric layer. The layered multiferroic structure in inhomogeneous electric and magnetic fields was calculated on the basis of the previously proposed mathematical model. The eigenwaves spectrum for several considered cases was the result of the performed calculation. The concept of using ME gradient structures in the design of electronically controlled microwave devices is formed on the basis of the results of a numerical experiment. Structures of this type will preferably be used in electronically controlled devices for the directional transmission of microwave signals, as it was shown in the theoretical part of the paper.

Solid solutions (SS) of 3- and 4-component systems based on lead titanate-zirconate were prepared by the method of solid-phase reactions and uniaxial hot pressing. The dependences of the relative permittivity of polarized samples on the electronegativity (EN) of their constituent cations have been studied. The ferro-hardness of the SS (the stability of the domain structure to external influences) is shown to be directly dependent on the EN of elements B in the corresponding oxidation states, i.e., the degree of covalence of the B–O bond. The deviation from this dependence in SS with Ni and Cd is explained by their individual features, which result in changes in the degree of bond covalence in both cationic sublattices. The conducted crystal-chemical analysis made it possible to choose promising SS when creating ferroelectric materials, including textured piezoelectric ceramic materials for piezoelectric transducers for various purposes: Piezotransformers, piezoelectric motors, ultrasonic emitters, filter devices, ultrasonic flaw detectors, accelerometers, etc.Solid solutions (SS) of 3- and 4-component systems based on lead titanate-zirconate were prepared by the method of solid-phase reactions and uniaxial hot pressing. The dependences of the relative permittivity of polarized samples on the electronegativity (EN) of their constituent cations have been studied. The ferro-hardness of the SS (the stability of the domain structure to external influences) is shown to be directly dependent on the EN of elements B in the corresponding oxidation states, i.e., the degree of covalence of the B–O bond. The deviation from this dependence in SS with Ni and Cd is explained by their individual features, which result in changes in the degree of bond covalence in both cationic sublattices. The conducted crystal-chemical analysis made it possible to choose promising SS when creating ferroelectric materials, including textured piezoelectric ceramic materials for piezoelectric transducers for various purposes: Piezotransformers, piezoelectric motors, ultrasonic emitters, filter devices, ultrasonic flaw detectors, accelerometers, etc.

In this paper, 0.36Pb(Ni1/3Nb2/3)O3–0.24PbZrO3–0.40PbTiO3(PNN-PZT) ceramic was prepared, and texture engineering was performed on this PNN-PZT ceramic to improve its electromechanical properties and temperature stability. Single element ultrasonic transducers were prepared using PNN-PZT, PNN-PZT textured ceramics, and their performance were evaluated and compared using a PZT-5H ceramic based transducer as the benchmark. It is shown that the sensitivity and bandwidth of the PNN-PZT textured ceramic-based transducer are much superior to regular PNN-PZT ceramic and PZT-5H ceramic based transducers.In this paper, 0.36Pb(Ni1/3Nb2/3)O3–0.24PbZrO3–0.40PbTiO3(PNN-PZT) ceramic was prepared, and texture engineering was performed on this PNN-PZT ceramic to improve its electromechanical properties and temperature stability. Single element ultrasonic transducers were prepared using PNN-PZT, PNN-PZT textured ceramics, and their performance were evaluated and compared using a PZT-5H ceramic based transducer as the benchmark. It is shown that the sensitivity and bandwidth of the PNN-PZT textured ceramic-based transducer are much superior to regular PNN-PZT ceramic and PZT-5H ceramic based transducers.

Crystallographic texturing enables the design of piezoelectric polycrystals that outperform traditional random polycrystals by exhibiting outstanding piezoelectric properties. In this work, phase-field modeling and computer simulation were employed to study the effect of crystallographic texture on the piezoelectric properties of ferroelectric polycrystals at the domain level. Domain evolutions for single crystal, random polycrystal, and textured polycrystal are systematically simulated. The simulations reveal that the [001]-textured polycrystal can fully exploit the intrinsic anisotropic properties of piezoelectric materials by exhibiting a piezoelectric coefficient that is as large as that of single crystal while being much larger than that of random polycrystal. To better understand the mechanism of piezoelectricity enhancement by crystallographic texturing, a theoretical analysis based on Landau theory is provided. In comparison with random polycrystal, the textured polycrystal manifests a flatter energy landscape and thus possesses a higher piezoelectric coefficient.Crystallographic texturing enables the design of piezoelectric polycrystals that outperform traditional random polycrystals by exhibiting outstanding piezoelectric properties. In this work, phase-field modeling and computer simulation were employed to study the effect of crystallographic texture on the piezoelectric properties of ferroelectric polycrystals at the domain level. Domain evolutions for single crystal, random polycrystal, and textured polycrystal are systematically simulated. The simulations reveal that the [001]-textured polycrystal can fully exploit the intrinsic anisotropic properties of piezoelectric materials by exhibiting a piezoelectric coefficient that is as large as that of single crystal while being much larger than that of random polycrystal. To better understand the mechanism of piezoelectricity enhancement by crystallographic texturing, a theoretical analysis based on Landau theory is provided. In comparison with random polycrystal, the textured polycrystal manifests a flatter energy landscape and thus possesses a higher piezoelectric coefficient.

This paper studies the dielectric spectra of solid solutions (SS) of the system (1 − x − y)NaNbO3–xKNbO3 –yCdNb2O6y= 0.075, x= 0.05 ÷ 0.30 in the temperature range (10 ÷ 900) K. The formation of a local maximum was established in the interval (260 ÷ 300) K at small x values, which, as KNbO3 increases, is gradually blurred and becomes an inflection point. Detected in SS with x = 0.05 ÷ 0.10, the shift of the maxima of dependences 𝜀′/ 𝜀0(T) and 𝜀′′/𝜀0 (T), depending on the frequency of the electric field at the temperature ranges (300 ÷ 304) K and (258 ÷ 271) K, is not related to relaxation. This anomaly may indicate a crystallographic disorder to A and B positions. The conclusion is made about the expediency of using the obtained results for the development of functional ferroactive materials.This paper studies the dielectric spectra of solid solutions (SS) of the system (1 − x − y)NaNbO3–xKNbO3 –yCdNb2O6y= 0.075, x= 0.05 ÷ 0.30 in the temperature range (10 ÷ 900) K. The formation of a local maximum was established in the interval (260 ÷ 300) K at small x values, which, as KNbO3 increases, is gradually blurred and becomes an inflection point. Detected in SS with x = 0.05 ÷ 0.10, the shift of the maxima of dependences 𝜀′/ 𝜀0(T) and 𝜀′′/𝜀0 (T), depending on the frequency of the electric field at the temperature ranges (300 ÷ 304) K and (258 ÷ 271) K, is not related to relaxation. This anomaly may indicate a crystallographic disorder to A and B positions. The conclusion is made about the expediency of using the obtained results for the development of functional ferroactive materials.

The theoretical possibility of the temperature-activation process of the temperature dependence of the dielectric constant of samples of ferroelectric ceramics lead zirconate titanate (PZT) at temperatures below the Curie point is considered. The model takes into account the 180° motion of the domain wall, which is located in the potential well. The values of activation energies (∼ 0.01, 0.1, 1 eV) were obtained from the experimental dependences of the logarithm of the dielectric constant on the reciprocal temperature. This is associated with three processes: initial vibrations of domain walls; separation of domain walls (DWs) from oxygen vacancies; the motion of DWs as a result of the motion of oxygen vacancies.The theoretical possibility of the temperature-activation process of the temperature dependence of the dielectric constant of samples of ferroelectric ceramics lead zirconate titanate (PZT) at temperatures below the Curie point is considered. The model takes into account the 180° motion of the domain wall, which is located in the potential well. The values of activation energies (∼ 0.01, 0.1, 1 eV) were obtained from the experimental dependences of the logarithm of the dielectric constant on the reciprocal temperature. This is associated with three processes: initial vibrations of domain walls; separation of domain walls (DWs) from oxygen vacancies; the motion of DWs as a result of the motion of oxygen vacancies.

In this work, Ba1−xCaxTi0.88Zr0.12O3 (x= 0.00–0.25) ceramics were prepared by a solid-state reaction method, and the variation of dielectric, ferroelectric and piezoelectric characteristics has been investigated together with the structure evolution. The crystal structure varies from rhombohedral to tetragonal at room-temperature and the morphotropic phase boundary (MPB) is determined around x= 0.10, where the significantly enhanced ferroelectric and piezoelectric properties are achieved. With the increase of Ca content, the system gradually evolves into a relaxor ferroelectric. This work provides useful guidance for future research on lead-free piezoelectric materials.In this work, Ba1−xCaxTi0.88Zr0.12O3 (x= 0.00–0.25) ceramics were prepared by a solid-state reaction method, and the variation of dielectric, ferroelectric and piezoelectric characteristics has been investigated together with the structure evolution. The crystal structure varies from rhombohedral to tetragonal at room-temperature and the morphotropic phase boundary (MPB) is determined around x= 0.10, where the significantly enhanced ferroelectric and piezoelectric properties are achieved. With the increase of Ca content, the system gradually evolves into a relaxor ferroelectric. This work provides useful guidance for future research on lead-free piezoelectric materials.

A phase-field model is developed in this paper based on the similarity between mechanical fracture and dielectric breakdown. Electrical treeing is associated with the dielectric breakdown in solid dielectrics by the application of high voltages. Instead of explicitly tracing the propagation of conductive channel, this model initializes a continuous phase field to characterize the extent of damage. So far, limited research has been conducted for simulating the effect of nanofiller dispersion on electrical treeing. No study has modeled the effect of uniform and nonuniform dispersion of nanofillers with varying filler concentration on treeing. Since electrical treeing tends to decrease the breakdown strength of solid dielectrics therefore, nanofillers are widely used to distract the tree from a straight channel to distribute its energy in multiple paths. Diverting a straight treeing channel into multiple paths reduces the chances of its propagation from live to dead-end hence, improving the breakdown strength. The physical and chemical nature of nanofillers has a crucial impact on increasing the resistance to treeing. In this paper, phase-field model is developed and used to simulate electrical treeing in polyethylene for varying concentrations of alumina nanofiller using COMSOL Multiphysics. Tree inception time, tree-growth patterns, and corresponding changes in dielectric strength is studied for both dispersions. Electrical treeing under different concentrations of alumina nanofillers with uniform and nonuniform dispersion is investigated in polyethylene as a base material. It is observed that fillers with uniform dispersion increases the resistance to treeing and tree inception time. Highest resistance to treeing is observed by adding 1% nanoalumina uniformly in raw polyethylene. Moreover, in uniform dispersion the tree deflects into multiple branches earlier than nonuniform dispersion impeding the damage speed as well.A phase-field model is developed in this paper based on the similarity between mechanical fracture and dielectric breakdown. Electrical treeing is associated with the dielectric breakdown in solid dielectrics by the application of high voltages. Instead of explicitly tracing the propagation of conductive channel, this model initializes a continuous phase field to characterize the extent of damage. So far, limited research has been conducted for simulating the effect of nanofiller dispersion on electrical treeing. No study has modeled the effect of uniform and nonuniform dispersion of nanofillers with varying filler concentration on treeing. Since electrical treeing tends to decrease the breakdown strength of solid dielectrics therefore, nanofillers are widely used to distract the tree from a straight channel to distribute its energy in multiple paths. Diverting a straight treeing channel into multiple paths reduces the chances of its propagation from live to dead-end hence, improving the breakdown strength. The physical and chemical nature of nanofillers has a crucial impact on increasing the resistance to treeing. In this paper, phase-field model is developed and used to simulate electrical treeing in polyethylene for varying concentrations of alumina nanofiller using COMSOL Multiphysics. Tree inception time, tree-growth patterns, and corresponding changes in dielectric strength is studied for both dispersions. Electrical treeing under different concentrations of alumina nanofillers with uniform and nonuniform dispersion is investigated in polyethylene as a base material. It is observed that fillers with uniform dispersion increases the resistance to treeing and tree inception time. Highest resistance to treeing is observed by adding 1% nanoalumina uniformly in raw polyethylene. Moreover, in uniform dispersion the tree deflects into multiple branches earlier than nonuniform dispersion impeding the damage speed as well.

Ferroelectric tunnel junction (FTJ) has attracted considerable attention for its potential applications in nonvolatile memory and neuromorphic computing. However, the experimental exploration of FTJs with high ON/OFF ratios is a challenging task due to the vast search space comprising of ferroelectric and electrode materials, fabrication methods and conditions and so on. Here, machine learning (ML) is demonstrated to be an effective tool to guide the experimental search of FTJs with high ON/OFF ratios. A dataset consisting of 152 FTJ samples with nine features and one target attribute (i.e., ON/OFF ratio) is established for ML modeling. Among various ML models, the gradient boosting classification model achieves the highest prediction accuracy. Combining the feature importance analysis based on this model with the association rule mining, it is extracted that the utilizations of {graphene/graphite (Gra) (top), LaNiO3 (LNO) (bottom)} and {Gra (top), Ca0.96Ce0.04MnO3 (CCMO) (bottom)} electrode pairs are likely to result in high ON/OFF ratios in FTJs. Moreover, two previously unexplored FTJs: Gra/BaTiO3 (BTO)/LNO and Gra/BTO/CCMO, are predicted to achieve ON/OFF ratios higher than 1000. Guided by the ML predictions, the Gra/BTO/LNO and Gra/BTO/CCMO FTJs are experimentally fabricated, which unsurprisingly exhibit ≥1000 ON/OFF ratios (∼8540 and ∼7890, respectively). This study demonstrates a new paradigm of developing high-performance FTJs by using ML.Ferroelectric tunnel junction (FTJ) has attracted considerable attention for its potential applications in nonvolatile memory and neuromorphic computing. However, the experimental exploration of FTJs with high ON/OFF ratios is a challenging task due to the vast search space comprising of ferroelectric and electrode materials, fabrication methods and conditions and so on. Here, machine learning (ML) is demonstrated to be an effective tool to guide the experimental search of FTJs with high ON/OFF ratios. A dataset consisting of 152 FTJ samples with nine features and one target attribute (i.e., ON/OFF ratio) is established for ML modeling. Among various ML models, the gradient boosting classification model achieves the highest prediction accuracy. Combining the feature importance analysis based on this model with the association rule mining, it is extracted that the utilizations of {graphene/graphite (Gra) (top), LaNiO3 (LNO) (bottom)} and {Gra (top), Ca0.96Ce0.04MnO3 (CCMO) (bottom)} electrode pairs are likely to result in high ON/OFF ratios in FTJs. Moreover, two previously unexplored FTJs: Gra/BaTiO3 (BTO)/LNO and Gra/BTO/CCMO, are predicted to achieve ON/OFF ratios higher than 1000. Guided by the ML predictions, the Gra/BTO/LNO and Gra/BTO/CCMO FTJs are experimentally fabricated, which unsurprisingly exhibit ≥1000 ON/OFF ratios (∼8540 and ∼7890, respectively). This study demonstrates a new paradigm of developing high-performance FTJs by using ML.

A novel category of polyphenylene oxide/high-impact polystyrene (PPO/HIPS) alloy was used as the polymer matrix (abbreviated as mPPO) and loaded with different volume fractions (0, 10, 20, 30, 40, 50 vol.%) of MgTiO3–Ca0.7La0.2TiO3 (abbreviated as MTCLT) ceramics to prepare composites by injection molding. Its micromorphology, density, dielectric, thermal and mechanical properties were analyzed in detail. The experimental results show that the composites possess a compact microstructure because HIPS increases the fluidity of PPO. Due to the excellent dielectric properties of both mPPO and MTCLT, the composites have an extremely low dielectric loss. The realization of the high ceramic filler fraction greatly limits the thermal expansion of the polymer chain by introducing the interphase, so that the coefficient of thermal expansion of the composite material could be as low as 21.8 ppm/∘C. At the same time, the presence of ceramic particles could reinforce the mechanical property of the composites. When the ceramic filler fraction is higher than 20 vol.%, the bending strength of the composite material is around 110 MPa. When the ceramic filler fraction is 40 vol.%, the composite possesses the best comprehensive performance. The dielectric constant is 6.81, the dielectric loss is 0.00104, the thermal expansion coefficient is as low as 25.3 ppm/∘C, and the bending strength is 110.4 MPa. Due to its excellent properties, this material can be a good candidate in the field of microwave communication.A novel category of polyphenylene oxide/high-impact polystyrene (PPO/HIPS) alloy was used as the polymer matrix (abbreviated as mPPO) and loaded with different volume fractions (0, 10, 20, 30, 40, 50 vol.%) of MgTiO3–Ca0.7La0.2TiO3 (abbreviated as MTCLT) ceramics to prepare composites by injection molding. Its micromorphology, density, dielectric, thermal and mechanical properties were analyzed in detail. The experimental results show that the composites possess a compact microstructure because HIPS increases the fluidity of PPO. Due to the excellent dielectric properties of both mPPO and MTCLT, the composites have an extremely low dielectric loss. The realization of the high ceramic filler fraction greatly limits the thermal expansion of the polymer chain by introducing the interphase, so that the coefficient of thermal expansion of the composite material could be as low as 21.8 ppm/∘C. At the same time, the presence of ceramic particles could reinforce the mechanical property of the composites. When the ceramic filler fraction is higher than 20 vol.%, the bending strength of the composite material is around 110 MPa. When the ceramic filler fraction is 40 vol.%, the composite possesses the best comprehensive performance. The dielectric constant is 6.81, the dielectric loss is 0.00104, the thermal expansion coefficient is as low as 25.3 ppm/∘C, and the bending strength is 110.4 MPa. Due to its excellent properties, this material can be a good candidate in the field of microwave communication.

This work harmonizes the experimental and theoretical study of electrocaloric effect (ECE) in (Pb0.8Bi0.2)(Zr0.52Ti0.48)O3 solid solution by optimizing sintering temperature. Bi3+-doped PbZr0.52Ti0.48O3 solid solutions were synthesized by the conventional solid-state reaction method. Different samples were prepared by varying the sintering temperature. X-ray diffraction study confirms the crystalline nature of all the samples. An immense value of polarization has been acquired in the optimized sample. The maximum adiabatic temperature change of order 2.53 K with electrocaloric strength of 1.26 K mm kV−1 has been achieved experimentally. Whereas a comparatively close value of ECE has been acquired from the theoretical calculations using a phenomenological approach. Furthermore, a large value (218 mJ cm−3) of thermal energy conversion has been obtained using the Olsen cycle.This work harmonizes the experimental and theoretical study of electrocaloric effect (ECE) in (Pb0.8Bi0.2)(Zr0.52Ti0.48)O3 solid solution by optimizing sintering temperature. Bi3+-doped PbZr0.52Ti0.48O3 solid solutions were synthesized by the conventional solid-state reaction method. Different samples were prepared by varying the sintering temperature. X-ray diffraction study confirms the crystalline nature of all the samples. An immense value of polarization has been acquired in the optimized sample. The maximum adiabatic temperature change of order 2.53 K with electrocaloric strength of 1.26 K mm kV−1 has been achieved experimentally. Whereas a comparatively close value of ECE has been acquired from the theoretical calculations using a phenomenological approach. Furthermore, a large value (218 mJ cm−3) of thermal energy conversion has been obtained using the Olsen cycle.

A series of (100−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMN−xPT, x= 24, 25, 26) ceramics were prepared by solid-state reaction technique using MgNb2O6 precursor. The results of the detailed characterizations reveal that the content of PT has negligible influence on the grain size, and all samples possess the perovskite structure. As the PT content increases, the samples changed from the normal ferroelectric phase to the ergodic relaxor state at room temperature. As a result, PMN–xPT ceramics are endowed with electro-strain of 0.08% at a relatively low electric field of 2 kV/mm, and effective piezoelectric coefficient of 320 pm/V was obtained. Simultaneously, the PMN–xPT ceramics have exceptional pyroelectric performance, exhibiting a high pyroelectric coefficient p∼5.5 – 6.3 × 10−8 C⋅cm−2⋅K−1. This study demonstrates the great potential of PMN–xPT for piezoelectric and pyroelectric device applications.A series of (100−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 (PMN−xPT, x= 24, 25, 26) ceramics were prepared by solid-state reaction technique using MgNb2O6 precursor. The results of the detailed characterizations reveal that the content of PT has negligible influence on the grain size, and all samples possess the perovskite structure. As the PT content increases, the samples changed from the normal ferroelectric phase to the ergodic relaxor state at room temperature. As a result, PMN–xPT ceramics are endowed with electro-strain of 0.08% at a relatively low electric field of 2 kV/mm, and effective piezoelectric coefficient of 320 pm/V was obtained. Simultaneously, the PMN–xPT ceramics have exceptional pyroelectric performance, exhibiting a high pyroelectric coefficient p∼5.5 – 6.3 × 10−8 C⋅cm−2⋅K−1. This study demonstrates the great potential of PMN–xPT for piezoelectric and pyroelectric device applications.

The polycrystalline NaMgPO4 ceramic, synthesized via a high-temperature solid-state reaction route, has been characterized by using different experimental procedures. The X-ray powder diffraction confirmed the phase formation of the synthesized compound in the orthorhombic phase. It assumed an olivine-type structure made up of corners linked between tetrahedral PO4 and octahedral NaO6 and MgO6 groups. Infrared and Raman spectroscopies confirmed the presence of PO43− groups. Local structure and chemical bonding between MgO6 octahedral and PO43− tetrahedral groups investigated by diffusion Raman is the feature in the phase transition at T= 693 K. The temperature dependences of the real 𝜀′ and imaginary 𝜀′ parts of dielectric permittivity show a distribution of relaxation times. From Nyquist plots, the presence of grain and grain boundary effect in the material is noticed. The impedance spectroscopy measurement showed a non-Debye-type process. From the impedance data, the determined grain resistance reduces with increment of temperature showing negative temperature coefficient of resistance (NTCR)-type nature of the material which also confirmed from conductivity analysis. The temperature dependence of σdc reveals an Arrhenius-type behavior with two activation energies, 0.98 eV in region I and 0.67 eV in region II. Studied sample’s conduction is assured by Na+ ions’ hopping in tunnels and its mechanism was discussed.The polycrystalline NaMgPO4 ceramic, synthesized via a high-temperature solid-state reaction route, has been characterized by using different experimental procedures. The X-ray powder diffraction confirmed the phase formation of the synthesized compound in the orthorhombic phase. It assumed an olivine-type structure made up of corners linked between tetrahedral PO4 and octahedral NaO6 and MgO6 groups. Infrared and Raman spectroscopies confirmed the presence of PO43− groups. Local structure and chemical bonding between MgO6 octahedral and PO43− tetrahedral groups investigated by diffusion Raman is the feature in the phase transition at T= 693 K. The temperature dependences of the real 𝜀′ and imaginary 𝜀′ parts of dielectric permittivity show a distribution of relaxation times. From Nyquist plots, the presence of grain and grain boundary effect in the material is noticed. The impedance spectroscopy measurement showed a non-Debye-type process. From the impedance data, the determined grain resistance reduces with increment of temperature showing negative temperature coefficient of resistance (NTCR)-type nature of the material which also confirmed from conductivity analysis. The temperature dependence of σdc reveals an Arrhenius-type behavior with two activation energies, 0.98 eV in region I and 0.67 eV in region II. Studied sample’s conduction is assured by Na+ ions’ hopping in tunnels and its mechanism was discussed.

Pb0.96Sr0.04(Zr,Ti)0.7(Zn1/3Nb2/3)0.3O3 (PZN–PZT) piezoceramics with various Zr/Ti ratios and Li2CO3 sintering aid were sintered at 900∘C by the solid-state reaction route. The samples with different Zr/Ti ratios were compared according to microstructure, phase structure, piezoelectricity, ferroelectricity, and dielectric relaxation. The Zr/Ti ratio in the PZN–PZT ceramics greatly affects the electrical properties. The Zr/Ti ratio affects the proportion between the rhombohedral and tetragonal phases and also affects the grain size. The PZN–PZT ceramics with the Zr/Ti ratio of 53:47 have the largest grain size and have optimized piezoelectric properties (kp = 0.58, d33 = 540 pC/N, and TC = 250∘C). The larger the grain size, the lesser the grain boundary, the easier the domain wall motion, and the better the piezoelectric properties. The PZT ceramic with Zr/Ti ratio of 53:47 locates the morphotropic phase boundary (MPB) region which is one of the key factors for the high piezoelectric properties of the PZT.Pb0.96Sr0.04(Zr,Ti)0.7(Zn1/3Nb2/3)0.3O3 (PZN–PZT) piezoceramics with various Zr/Ti ratios and Li2CO3 sintering aid were sintered at 900∘C by the solid-state reaction route. The samples with different Zr/Ti ratios were compared according to microstructure, phase structure, piezoelectricity, ferroelectricity, and dielectric relaxation. The Zr/Ti ratio in the PZN–PZT ceramics greatly affects the electrical properties. The Zr/Ti ratio affects the proportion between the rhombohedral and tetragonal phases and also affects the grain size. The PZN–PZT ceramics with the Zr/Ti ratio of 53:47 have the largest grain size and have optimized piezoelectric properties (kp = 0.58, d33 = 540 pC/N, and TC = 250∘C). The larger the grain size, the lesser the grain boundary, the easier the domain wall motion, and the better the piezoelectric properties. The PZT ceramic with Zr/Ti ratio of 53:47 locates the morphotropic phase boundary (MPB) region which is one of the key factors for the high piezoelectric properties of the PZT.

This paper reports the impact of the laser pulse repetition frequency on growth processes, morphological and electro-physical parameters of nanocrystalline LiNbO3 thin films obtained by the pulsed laser deposition technique. It was found that the nucleation process in LiNbO3 films could controllably change by increasing the laser pulse repetition frequency. The film obtained at the repetition frequency of 4 Hz consists of local islands and clusters with a diameter of 118.1 ± 5.9 nm. Nanocrystalline films, grown at the repetition frequency of 10 Hz, possess a continuous granular structure with a grain diameter of 235 ± 11.75 nm. Achieved results can be used for the development of promising “green” energy devices based on lead-free piezoelectric energy harvesters.This paper reports the impact of the laser pulse repetition frequency on growth processes, morphological and electro-physical parameters of nanocrystalline LiNbO3 thin films obtained by the pulsed laser deposition technique. It was found that the nucleation process in LiNbO3 films could controllably change by increasing the laser pulse repetition frequency. The film obtained at the repetition frequency of 4 Hz consists of local islands and clusters with a diameter of 118.1 ± 5.9 nm. Nanocrystalline films, grown at the repetition frequency of 10 Hz, possess a continuous granular structure with a grain diameter of 235 ± 11.75 nm. Achieved results can be used for the development of promising “green” energy devices based on lead-free piezoelectric energy harvesters.

The comparative analysis of the dielectric properties of bismuth-containing pyrochlores with different manifestation of atomic order/disorder was carried out. We examined the dielectric properties (including behavior in electric fields) of two pyrochlore compounds: BZN (presumably a composition close to Bi1.5Zn0.5Nb1.5O6.5) ceramics with chemical disorder in both A and B cation sublattices and Bi2Ti2O7 single crystal with fully chemical ordered structure. The fundamental differences between the dielectric properties of the BZN ceramics and Bi2Ti2O7 single crystal were shown. In particular, in the dielectric relaxation behavior (which cannot be described via Arrhenius law in the Bi2Ti2O7) or in the influence of the electric fields on the dielectric permittivity (splitting of the field-cooled and zero-field-cooled behaviors was observed for Bi2Ti2O7 below estimated freezing temperature). The results of this study highlights the special role of Bi2Ti2O7 as a candidate material for studying aspects of geometric frustration related with pyrochlore structure in non-magnetic medium and specifies the future directions of research.The comparative analysis of the dielectric properties of bismuth-containing pyrochlores with different manifestation of atomic order/disorder was carried out. We examined the dielectric properties (including behavior in electric fields) of two pyrochlore compounds: BZN (presumably a composition close to Bi1.5Zn0.5Nb1.5O6.5) ceramics with chemical disorder in both A and B cation sublattices and Bi2Ti2O7 single crystal with fully chemical ordered structure. The fundamental differences between the dielectric properties of the BZN ceramics and Bi2Ti2O7 single crystal were shown. In particular, in the dielectric relaxation behavior (which cannot be described via Arrhenius law in the Bi2Ti2O7) or in the influence of the electric fields on the dielectric permittivity (splitting of the field-cooled and zero-field-cooled behaviors was observed for Bi2Ti2O7 below estimated freezing temperature). The results of this study highlights the special role of Bi2Ti2O7 as a candidate material for studying aspects of geometric frustration related with pyrochlore structure in non-magnetic medium and specifies the future directions of research.

In this paper, a comprehensive study of microstructure/properties interrelations for porous piezoceramics based on PZT composition was performed. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. Porosity dependencies of elastic, dielectric, piezoelectric and electromechanical coefficients of the porous ceramics in the relative porosity range 0-50% were obtained and analyzed. As a result of microstructure analysis, it was found that at any connectivity type (3–0, 3–3) and porosity up to 50% the real structures of porous piezoceramics were close to the matrix medium structure with continuous piezoceramic skeleton. It was also revealed that the microstructural features of porous piezoceramics define the character of the dependences of the dielectric, piezoelectric and electromechanical properties of porous piezoelectric ceramics on porosity. In conclusion, microstructure/properties interrelations, as well as new applications of porous piezoceramics were discussed.In this paper, a comprehensive study of microstructure/properties interrelations for porous piezoceramics based on PZT composition was performed. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. Porosity dependencies of elastic, dielectric, piezoelectric and electromechanical coefficients of the porous ceramics in the relative porosity range 0-50% were obtained and analyzed. As a result of microstructure analysis, it was found that at any connectivity type (3–0, 3–3) and porosity up to 50% the real structures of porous piezoceramics were close to the matrix medium structure with continuous piezoceramic skeleton. It was also revealed that the microstructural features of porous piezoceramics define the character of the dependences of the dielectric, piezoelectric and electromechanical properties of porous piezoelectric ceramics on porosity. In conclusion, microstructure/properties interrelations, as well as new applications of porous piezoceramics were discussed.

Solid solutions of the composition Ba1−x−y(Mg, Ln)xSryTiO3 (x = 0.01; 0.025; 0.04; y = 0.20; 0.50; 0.80; Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tu, Yb) were prepared by two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. The influence of rare-earth elements on the microstructure of the prepared ceramic samples was investigated. It was found that regardless of the type of modifiers introduced, the grain landscape of the studied solid solutions with different amounts of SrTiO3 is refined (in the initial system, the average grain size, d̄, at x = 0.20 is 6 μm; at x = 0.50 is 4 μm; at x = 0.80 is 18 μm) to crystallite sizes not exceeding (2-3) μm, and compacted. The using of mechanical activation procedures leads to an even greater decrease in the size and an increase in the density of ceramics. The increasing in the concentration of modifiers in each group (within the considered range of dopant variation) against the background of such a fine-grained structure has little effect on the dynamics of changes in d̄. It is concluded that it is advisable to use the data obtained in the development of functional materials based on BST/(Mg, Ln) and devices with the participation of these compositions.Solid solutions of the composition Ba1−x−y(Mg, Ln)xSryTiO3 (x = 0.01; 0.025; 0.04; y = 0.20; 0.50; 0.80; Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tu, Yb) were prepared by two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. The influence of rare-earth elements on the microstructure of the prepared ceramic samples was investigated. It was found that regardless of the type of modifiers introduced, the grain landscape of the studied solid solutions with different amounts of SrTiO3 is refined (in the initial system, the average grain size, d̄, at x = 0.20 is 6 μm; at x = 0.50 is 4 μm; at x = 0.80 is 18 μm) to crystallite sizes not exceeding (2-3) μm, and compacted. The using of mechanical activation procedures leads to an even greater decrease in the size and an increase in the density of ceramics. The increasing in the concentration of modifiers in each group (within the considered range of dopant variation) against the background of such a fine-grained structure has little effect on the dynamics of changes in d̄. It is concluded that it is advisable to use the data obtained in the development of functional materials based on BST/(Mg, Ln) and devices with the participation of these compositions.

In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.In this paper, the results of experimental study of dispersion characteristics of complex electromechanical parameters of ferroelectrically “hard” porous piezoceramics based on PZT composition were presented. Experimental samples of porous piezoceramics were fabricated using a modified method of burning-out a pore former. The complex constants of porous piezoceramics with relative porosity 16% and their frequency dependences were measured using the piezoelectric resonance analysis method. As a result of experimental studies, regions of elastic, piezoelectric and electromechanical dispersion, characterized by anomalies in the frequency dependences of the imaginary and real parts of the complex constants of porous piezoelectric ceramics were found. It was revealed also that the microstructural features of porous piezoceramics determine the character of frequency dependences of complex electromechanical parameters of porous piezoelectric ceramics. In conclusion, the microstructural and physical mechanisms of electromechanical losses and dispersion in porous piezoceramics were discussed.

Erbium-doped barium titanate (BaTiO3:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate (SrTiO3) xerogel film on Si substrate after annealing at 800∘C or 900∘C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2, 4F9/2→4I15/2 and 4I9/2→4I15/2 transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO3:Er\porous SrTiO3\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.Erbium-doped barium titanate (BaTiO3:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate (SrTiO3) xerogel film on Si substrate after annealing at 800∘C or 900∘C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to 2H11/2→4I15/2, 4S3/2→4I15/2, 4F9/2→4I15/2 and 4I9/2→4I15/2 transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO3:Er\porous SrTiO3\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.

In this study, the double-layered Aurivillius phases CaBi2Ta2O9 (CBT) and PbBi2Ta2O9 (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A21am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca2+ compared to Pb2+. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of A-site cations (Ca2+ and Pb2+) strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca2+ cations induced a higher structural distortion, which resulted in higher bandgap (Eg) energy and ferroelectric transition temperature (Tc) of CBT, compared to those of PBT.In this study, the double-layered Aurivillius phases CaBi2Ta2O9 (CBT) and PbBi2Ta2O9 (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an A21am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca2+ compared to Pb2+. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of A-site cations (Ca2+ and Pb2+) strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca2+ cations induced a higher structural distortion, which resulted in higher bandgap (Eg) energy and ferroelectric transition temperature (Tc) of CBT, compared to those of PBT.

Ceramics of quasi-binary concentration section (x = 0.50, 0.1 ≤y≤ 0.2, Δy = 0.025) of the ternary solid solution system (1−x−y)BiFeO3–xPbFe0.5Nb0.5O3–yPbTiO3 were prepared by the conventional solid-phase reaction method. By using X-ray diffraction technique, the phase diagram of the system was constructed, which was shown to contain the regions of cubic and tetragonal symmetry and the morphotropic phase boundary between them. Grain morphology, dielectric and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient d33= 260 pC/N was obtained. Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior, a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 350–500 K.Ceramics of quasi-binary concentration section (x = 0.50, 0.1 ≤y≤ 0.2, Δy = 0.025) of the ternary solid solution system (1−x−y)BiFeO3–xPbFe0.5Nb0.5O3–yPbTiO3 were prepared by the conventional solid-phase reaction method. By using X-ray diffraction technique, the phase diagram of the system was constructed, which was shown to contain the regions of cubic and tetragonal symmetry and the morphotropic phase boundary between them. Grain morphology, dielectric and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient d33= 260 pC/N was obtained. Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior, a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 350–500 K.

Some of the known binary ABO3perovskites with ferro- (FE) or antiferroelectric (AFE) at TC and different magnetic phase transitions (PT): ferro-and antiferromagnetic at TN and also some of their solid solutions are considered. Some correlations between their FE or AFE and/or magnetic PTs temperatures, on the one hand, and their interatomic bond A–O strains, on the other hand, have been constructed. It is shown that in the plotted diagrams these temperatures change with a change in δAO values as follows: classical FEs are followed by multiferroics, starting with BiFeO3 and ending with YVO3, followed by classical AFEs. At the same time, the temperatures TC and TN experience maxima at the corresponding points for BiFeO3, then quickly decrease, and the difference between them, TC-TN, basically also decreases, slightly increasing along the way to the point EuTiO3. which made it possible to systematize these TC and TN.Some of the known binary ABO3perovskites with ferro- (FE) or antiferroelectric (AFE) at TC and different magnetic phase transitions (PT): ferro-and antiferromagnetic at TN and also some of their solid solutions are considered. Some correlations between their FE or AFE and/or magnetic PTs temperatures, on the one hand, and their interatomic bond A–O strains, on the other hand, have been constructed. It is shown that in the plotted diagrams these temperatures change with a change in δAO values as follows: classical FEs are followed by multiferroics, starting with BiFeO3 and ending with YVO3, followed by classical AFEs. At the same time, the temperatures TC and TN experience maxima at the corresponding points for BiFeO3, then quickly decrease, and the difference between them, TC-TN, basically also decreases, slightly increasing along the way to the point EuTiO3. which made it possible to systematize these TC and TN.

The paper discusses the features of the effect of modification with lithium carbonate on the dielectric dispersion of lead ferroniobate ceramics. The modifier has been previously shown to change the ways of the recrystallization sintering and therefore reduce the sintering temperature of the ceramics, increase their average grain size, and improve their dielectric and piezoelectric properties. In this study, the emphasis is placed on the analysis of the diffusion effects of the ferroelectric phase transition upon such modification considered from the standpoint of the chemical specifics of the modifier and its location in the structure of the parent compound.The paper discusses the features of the effect of modification with lithium carbonate on the dielectric dispersion of lead ferroniobate ceramics. The modifier has been previously shown to change the ways of the recrystallization sintering and therefore reduce the sintering temperature of the ceramics, increase their average grain size, and improve their dielectric and piezoelectric properties. In this study, the emphasis is placed on the analysis of the diffusion effects of the ferroelectric phase transition upon such modification considered from the standpoint of the chemical specifics of the modifier and its location in the structure of the parent compound.

Efficiency of the piezoelectric chemisensors may be considerably enhanced by use of zinc oxide nanorods as sensing elements. ZnO nanorod arrays being good piezoelectric materials possess large surface area, which provides extra benefits for chemisorption and photodetection. Highly oriented nanorod arrays are typically prepared onto highly crystalline substrates, whereas the nanorods growth onto metal contacts meets significant technological difficulties. In this paper, we report on carbothermal, electrochemical, and hydrothermal techniques of ZnO nanorod arrays synthesis on metal contacts. The optical and structural properties of the obtained nanorods were studied using scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, and luminescence spectroscopy. A reliable technique was developed for obtaining ohmic contact with the grown nanorods. I–U curves of prepared contact were studied. Carbothermal synthesis made it possible to obtain the most crystallinely perfect, homogeneous, and dense arrays of nanorods and control the concentration of point defects by changing the synthesis parameters over a wide range. The electrochemical synthesis demonstrated excellent results for synthesis of ZnO nanorods on the surface of resonator electrodes.Efficiency of the piezoelectric chemisensors may be considerably enhanced by use of zinc oxide nanorods as sensing elements. ZnO nanorod arrays being good piezoelectric materials possess large surface area, which provides extra benefits for chemisorption and photodetection. Highly oriented nanorod arrays are typically prepared onto highly crystalline substrates, whereas the nanorods growth onto metal contacts meets significant technological difficulties. In this paper, we report on carbothermal, electrochemical, and hydrothermal techniques of ZnO nanorod arrays synthesis on metal contacts. The optical and structural properties of the obtained nanorods were studied using scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, and luminescence spectroscopy. A reliable technique was developed for obtaining ohmic contact with the grown nanorods. I–U curves of prepared contact were studied. Carbothermal synthesis made it possible to obtain the most crystallinely perfect, homogeneous, and dense arrays of nanorods and control the concentration of point defects by changing the synthesis parameters over a wide range. The electrochemical synthesis demonstrated excellent results for synthesis of ZnO nanorods on the surface of resonator electrodes.

This work presents the results of studying the electrophysical properties of the YCu0.15Mn0.85O3 solid solution in the range of temperatures of T = 26–400∘C and frequency range of f = 102–105 Hz. A model description of the revealed dispersion of dielectric parameters in the material is made. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity was used as an approximation model. It is shown that the application of this model almost exactly describes the frequency behavior of the dielectric constant 𝜀′/𝜀0( f), the dielectric loss tangent tgδ( f) as well as the real and imaginary parts of complex conductivity γ′( f) and γ′′( f). The results of this work are an important step in identifying the opportunities and understanding the applications of this model.This work presents the results of studying the electrophysical properties of the YCu0.15Mn0.85O3 solid solution in the range of temperatures of T = 26–400∘C and frequency range of f = 102–105 Hz. A model description of the revealed dispersion of dielectric parameters in the material is made. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity was used as an approximation model. It is shown that the application of this model almost exactly describes the frequency behavior of the dielectric constant 𝜀′/𝜀0( f), the dielectric loss tangent tgδ( f) as well as the real and imaginary parts of complex conductivity γ′( f) and γ′′( f). The results of this work are an important step in identifying the opportunities and understanding the applications of this model.

Ceramic samples of BiFeO3-based perovskite solid solutions with the highly ordered complex perovskites PbFe1/2Sb1/2O3(PFS) and SrFe1/2Sb1/2O3 (SFS) were obtained using high-pressure synthesis at 4–6 GPa. Mössbauer studies revealed that BiFeO3-SFS compositions are characterized by a larger compositional inhomogeneity as compared to BiFeO3-PFS ones. In line with this result, concentration dependence of the magnetic phase transition temperature TN for BiFeO3-SFS compositions is close to the TN(x) dependence for BiFeO3solid solution with disordered perovskite PbFe1/2Nb1/2O3(PFN). In contrast to this TN(x) dependence for BiFeO3-PFS compositions nicely follows the theoretical TN(x) dependence calculated for the case of the ordered distribution of Fe3+ and non-magnetic Sb5+ ions in the lattice (chemical ordering).Ceramic samples of BiFeO3-based perovskite solid solutions with the highly ordered complex perovskites PbFe1/2Sb1/2O3(PFS) and SrFe1/2Sb1/2O3 (SFS) were obtained using high-pressure synthesis at 4–6 GPa. Mössbauer studies revealed that BiFeO3-SFS compositions are characterized by a larger compositional inhomogeneity as compared to BiFeO3-PFS ones. In line with this result, concentration dependence of the magnetic phase transition temperature TN for BiFeO3-SFS compositions is close to the TN(x) dependence for BiFeO3solid solution with disordered perovskite PbFe1/2Nb1/2O3(PFN). In contrast to this TN(x) dependence for BiFeO3-PFS compositions nicely follows the theoretical TN(x) dependence calculated for the case of the ordered distribution of Fe3+ and non-magnetic Sb5+ ions in the lattice (chemical ordering).

The properties studying results of ceramics based on strontium, calcium and sodium niobates, which vary from the conditions of synthesis, sintering, and mechanical processing, are presented. The evolution of the grain structure of objects is traced depending on their phase filling during concentration changes in the composition and thermodynamic prehistory (preparation conditions).The properties studying results of ceramics based on strontium, calcium and sodium niobates, which vary from the conditions of synthesis, sintering, and mechanical processing, are presented. The evolution of the grain structure of objects is traced depending on their phase filling during concentration changes in the composition and thermodynamic prehistory (preparation conditions).

In this paper, we report the successful growth of 0.5BiFeO3–0.5PbFe0.5Nb0.5O3/SrTiO3/Si(001) heterostructure using RF-cathode sputtering in an oxygen atmosphere. The deposited films have been investigated by X-ray diffractometry and spectroscopic ellipsometry (SE). 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 films on silicon substrates with a strontium titanate buffer layer are single-phase, polycrystalline with a texture in the 001 direction. The unit cell parameters calculated in the tetragonal approximation were c = 4.005 ± 0.001 Å; a = 3.995 ± 0.001 Å. The presence in the films of small unit cell deformation arising from different unit cells parameters of the film and substrate is observed. Dielectric properties and capacitance-voltage characteristics have been measured. The ellipsometric parameters have been obtained.In this paper, we report the successful growth of 0.5BiFeO3–0.5PbFe0.5Nb0.5O3/SrTiO3/Si(001) heterostructure using RF-cathode sputtering in an oxygen atmosphere. The deposited films have been investigated by X-ray diffractometry and spectroscopic ellipsometry (SE). 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 films on silicon substrates with a strontium titanate buffer layer are single-phase, polycrystalline with a texture in the 001 direction. The unit cell parameters calculated in the tetragonal approximation were c = 4.005 ± 0.001 Å; a = 3.995 ± 0.001 Å. The presence in the films of small unit cell deformation arising from different unit cells parameters of the film and substrate is observed. Dielectric properties and capacitance-voltage characteristics have been measured. The ellipsometric parameters have been obtained.

Photocatalytic degradation kinetics of Jurlewicz–Weron–Stanislavsky (JWS) type has been identified. Experimental data are taken from previous published works, and fitted with the JWS relaxation function as well as that of the Havriliak–Negami (HN) model. All experimental data can fit with either model fairly good. From the fitting parameters, the Jonscher indices are calculated and Jonscher diagram is plotted for the chemical kinetics of photocatalytic degradations. This work suggests that material parameters of photocatalysts can be well defined in the sense of fractional calculus.Photocatalytic degradation kinetics of Jurlewicz–Weron–Stanislavsky (JWS) type has been identified. Experimental data are taken from previous published works, and fitted with the JWS relaxation function as well as that of the Havriliak–Negami (HN) model. All experimental data can fit with either model fairly good. From the fitting parameters, the Jonscher indices are calculated and Jonscher diagram is plotted for the chemical kinetics of photocatalytic degradations. This work suggests that material parameters of photocatalysts can be well defined in the sense of fractional calculus.

Spinel ferrite Ni0.08Mn0.90Zn0.02Fe2O4 was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050∘ C, 1100∘ C and 1150∘ C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm−1 to 400 cm−1. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 μm to 0.88 μm. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity (Hc) and saturation magnetization (Ms). Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature (Tc) and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.Spinel ferrite Ni0.08Mn0.90Zn0.02Fe2O4 was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050∘ C, 1100∘ C and 1150∘ C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm−1 to 400 cm−1. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 μm to 0.88 μm. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity (Hc) and saturation magnetization (Ms). Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature (Tc) and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.

Monophasic and polycrystalline double perovskite Eu2CoMnO6 has been synthesized, and its structural characterization, frequency and temperature-dependent dielectric relaxation have been studied. Observed thermally activated dielectric relaxation was explained using the empirical Havriliak–Negami (HN) dielectric relaxation function with an estimated activation energy E∼ 0.22 eV and attempt frequency f0∼ 2.46 × 109 Hz. The frequency-dependent AC conductivity data, over a wide range of temperature (100–325 K), followed the empirical universal power law behavior (∼fn, n is the constant exponent) showing two different frequency exponents, respectively, in the high- and low-temperature regions. The high-temperature (> 275 K) conductivity data followed the continuous time random walk (CTRW) approximation model proposed by Dyre. However, this model failed to reproduce the observed conductivity spectra in the low-temperature side ( 200 K). Interestingly, both the high- and low-temperatures’ conductivity data can be scaled to the master curve with suitably chosen scaling parameters.Monophasic and polycrystalline double perovskite Eu2CoMnO6 has been synthesized, and its structural characterization, frequency and temperature-dependent dielectric relaxation have been studied. Observed thermally activated dielectric relaxation was explained using the empirical Havriliak–Negami (HN) dielectric relaxation function with an estimated activation energy E∼ 0.22 eV and attempt frequency f0∼ 2.46 × 109 Hz. The frequency-dependent AC conductivity data, over a wide range of temperature (100–325 K), followed the empirical universal power law behavior (∼fn, n is the constant exponent) showing two different frequency exponents, respectively, in the high- and low-temperature regions. The high-temperature (> 275 K) conductivity data followed the continuous time random walk (CTRW) approximation model proposed by Dyre. However, this model failed to reproduce the observed conductivity spectra in the low-temperature side ( 200 K). Interestingly, both the high- and low-temperatures’ conductivity data can be scaled to the master curve with suitably chosen scaling parameters.

The U-type hexaferrites (Ba1−3xLa2x)4Co2Fe36O60 (x= 0, 0.05, 0.10, 0.15, 0.20, 0.25) have been synthesized by auto-combustion method. The work involves the study of structural, microstructural, dielectric, magnetic and magneto-dielectric properties of the prepared materials. The structural analysis has been done by X-ray diffraction technique along with Le Bail refinement which confirmed the pure hexagonal phase for all the samples. The microstructural analysis has been carried out by field-emission scanning electron microscopy. The vibrating sample magnetometer is used to measure the magnetic properties. The sample with a composition of x= 0.15 has shown the maximum magnetization of approximately 73.31 emu/g with the remnant magnetization of 38.89 emu/g and coercive field of 1.77 kOe at room temperature. Moreover, the same sample has delivered the maximum magneto-dielectric response of about 54.18% at 1.5-T field.The U-type hexaferrites (Ba1−3xLa2x)4Co2Fe36O60 (x= 0, 0.05, 0.10, 0.15, 0.20, 0.25) have been synthesized by auto-combustion method. The work involves the study of structural, microstructural, dielectric, magnetic and magneto-dielectric properties of the prepared materials. The structural analysis has been done by X-ray diffraction technique along with Le Bail refinement which confirmed the pure hexagonal phase for all the samples. The microstructural analysis has been carried out by field-emission scanning electron microscopy. The vibrating sample magnetometer is used to measure the magnetic properties. The sample with a composition of x= 0.15 has shown the maximum magnetization of approximately 73.31 emu/g with the remnant magnetization of 38.89 emu/g and coercive field of 1.77 kOe at room temperature. Moreover, the same sample has delivered the maximum magneto-dielectric response of about 54.18% at 1.5-T field.

Frequency-dependent dielectric constant, dielectric loss, AC conductivity values and complex impedance spectra of V2O5-added Ni–Co–Zn ferrites (Ni0.62Co0.03Zn0.35Fe2O4+xV2O5, where x= 0, 0.5, 1 and 1.5 wt.%) have been investigated at room temperature. The dielectric properties of the samples follow the Maxwell–Wagner polarization model. An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples. The dielectric constants decreased with the addition of V2O5, while the electrical resistivities of V2O5-added Ni–Co–Zn ferrites are found to be larger than that of pure Ni–Co–Zn ferrite. The AC conductivity was reduced with the addition of V2O5to Ni–Co–Zn ferrite at lower-frequency region. However, AC conductivity shows a sharp increase at higher-frequency region, which could be attributed to the enhancement of electron hopping between the Fe2+ and Fe3+ ions in the ferrite matrix due to the activity of the grains. The complex impedance spectroscopy results through Cole–Cole/Nyquist plot have demonstrated a single semicircular arc. It indicates that conduction mechanism takes place predominantly through the grain/bulk property, which could be ascribed to the larger grain size of V2O5-added Ni–Co–Zn ferrites.Frequency-dependent dielectric constant, dielectric loss, AC conductivity values and complex impedance spectra of V2O5-added Ni–Co–Zn ferrites (Ni0.62Co0.03Zn0.35Fe2O4+xV2O5, where x= 0, 0.5, 1 and 1.5 wt.%) have been investigated at room temperature. The dielectric properties of the samples follow the Maxwell–Wagner polarization model. An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples. The dielectric constants decreased with the addition of V2O5, while the electrical resistivities of V2O5-added Ni–Co–Zn ferrites are found to be larger than that of pure Ni–Co–Zn ferrite. The AC conductivity was reduced with the addition of V2O5to Ni–Co–Zn ferrite at lower-frequency region. However, AC conductivity shows a sharp increase at higher-frequency region, which could be attributed to the enhancement of electron hopping between the Fe2+ and Fe3+ ions in the ferrite matrix due to the activity of the grains. The complex impedance spectroscopy results through Cole–Cole/Nyquist plot have demonstrated a single semicircular arc. It indicates that conduction mechanism takes place predominantly through the grain/bulk property, which could be ascribed to the larger grain size of V2O5-added Ni–Co–Zn ferrites.

Ba0.85Ca0.15(Ti1−xZrx)O3(BCTZ) ceramics with x= 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 were prepared by the solid-state reaction method. Calcination of the powders was carried out at 1100 ∘C for 4 h and the green pellets were sintered at 1400 ∘C for 2 h. X-ray diffraction patterns of the sintered pellets showed tetragonal splitting up to x= 0.10 while the mixture of the rhombohedral/cubic phase appeared at higher ZrO2 concentrations. Maximum piezoelectric charge constant d33= 510 pC/N and strain (S= 0.103%) were measured for BCT doped by 0.10 mol ZrO2. Dielectric constant, remnant polarization and saturation polarization also found maxima for this composition. The Curie temperature (TC) of the compositions decreased with increase in ZrO2 concentration and reached 98 ∘C, 87 ∘C and 36 ∘C at x= 0.05, 0.10, 0.15 mol, respectively. The remaining compositions have TC below the room temperature; therefore, they can be used for subzero/cryogenic applications. The scanning electron microscopy study revealed an increase in grain size with increase in ZrO2 concentration and confirmed the complete solubility of ZrO2 in the crystal lattice. Overall, low ZrO2-doped BCT compositions with high d33 could be suitable for low temperature (∘C) applications.Ba0.85Ca0.15(Ti1−xZrx)O3(BCTZ) ceramics with x= 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 were prepared by the solid-state reaction method. Calcination of the powders was carried out at 1100 ∘C for 4 h and the green pellets were sintered at 1400 ∘C for 2 h. X-ray diffraction patterns of the sintered pellets showed tetragonal splitting up to x= 0.10 while the mixture of the rhombohedral/cubic phase appeared at higher ZrO2 concentrations. Maximum piezoelectric charge constant d33= 510 pC/N and strain (S= 0.103%) were measured for BCT doped by 0.10 mol ZrO2. Dielectric constant, remnant polarization and saturation polarization also found maxima for this composition. The Curie temperature (TC) of the compositions decreased with increase in ZrO2 concentration and reached 98 ∘C, 87 ∘C and 36 ∘C at x= 0.05, 0.10, 0.15 mol, respectively. The remaining compositions have TC below the room temperature; therefore, they can be used for subzero/cryogenic applications. The scanning electron microscopy study revealed an increase in grain size with increase in ZrO2 concentration and confirmed the complete solubility of ZrO2 in the crystal lattice. Overall, low ZrO2-doped BCT compositions with high d33 could be suitable for low temperature (∘C) applications.

The dielectric and pyroelectric performances of 91.5Na0.5Bi0.5TiO3–8.5K0.5Bi0.5TiO3 lead-free single crystal were investigated. The depolarization temperature of the crystal is about 153 ∘C. Among the , , and crystallographic orientations, the -oriented crystal possesses the highest pyroelectric coefficient and the largest figures of merit, and the values of p, Fv, and Fdare 5.63×10−4 C/m2 •K, 0.06 m2/C, and 21.5 μPa−1/2 for the -oriented crystal at room temperature. The Fdand Fvexhibit weak frequency dependence in the range of 100–300 Hz. With the increase of the temperature, the value of pincreases, while the value of Fv decreases from 18 ∘C to 103 ∘C.The dielectric and pyroelectric performances of 91.5Na0.5Bi0.5TiO3–8.5K0.5Bi0.5TiO3 lead-free single crystal were investigated. The depolarization temperature of the crystal is about 153 ∘C. Among the , , and crystallographic orientations, the -oriented crystal possesses the highest pyroelectric coefficient and the largest figures of merit, and the values of p, Fv, and Fdare 5.63×10−4 C/m2 •K, 0.06 m2/C, and 21.5 μPa−1/2 for the -oriented crystal at room temperature. The Fdand Fvexhibit weak frequency dependence in the range of 100–300 Hz. With the increase of the temperature, the value of pincreases, while the value of Fv decreases from 18 ∘C to 103 ∘C.

Bismuth ferrite (BFO) nanostructures and thin films have gained attraction as suitable candidates for energy storage and energy conversion due to their high energy storage efficiency, temperature stability and low dielectric loss. Electrical properties of such multiferroic materials are tailored by ferroelectric and ferromagnetic constituents and have opened up amazing avenues in electrochemical supercapacitor and photovoltaic applications. Dopants play a significant role in optimizing the magnetic and dielectric properties of such materials owing to suitable applications. This review highlights the scientific advancements reported in BFO nanostructures for energy applications by optimizing their magnetic and dielectric properties. This paper starts with a brief introduction of BFO and a discussion on the effects of various dopants by different synthesis techniques, and their effects on the magnetic and dielectric properties are also portrayed. Eventually, this review summarizes the various doping effects, which paves way for future research on this multiferroic material.Bismuth ferrite (BFO) nanostructures and thin films have gained attraction as suitable candidates for energy storage and energy conversion due to their high energy storage efficiency, temperature stability and low dielectric loss. Electrical properties of such multiferroic materials are tailored by ferroelectric and ferromagnetic constituents and have opened up amazing avenues in electrochemical supercapacitor and photovoltaic applications. Dopants play a significant role in optimizing the magnetic and dielectric properties of such materials owing to suitable applications. This review highlights the scientific advancements reported in BFO nanostructures for energy applications by optimizing their magnetic and dielectric properties. This paper starts with a brief introduction of BFO and a discussion on the effects of various dopants by different synthesis techniques, and their effects on the magnetic and dielectric properties are also portrayed. Eventually, this review summarizes the various doping effects, which paves way for future research on this multiferroic material.

The electrophysical and structural characteristics of bismuth titanate oxides of a number of phases of solid solutions of the Aurivillius phases Bi7−2xNd2xTi4NbO21 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) having a layered structure of the perovskite type have been investigated. According to the XRD data, all studied compounds are single-phase and have a mixed-layer structure of Aurivillius phases (m = 2.5) with a rhombic crystal lattice (space group I2cm, Z = 2). A relationship has been established between changes in the chemical composition of solid solutions and orthorhombic and tetragonal distortions of perovskite-like layers. The temperature dependences of the relative permittivity 𝜀/𝜀o(T) are measured. It was found that the change in the phase transition temperature — Curie temperature TC synthesized Aurivillius phases Bi7−xNd2xTi4NbO21 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) has a close to linear dependence on the change in the parameter x. The activation energies of charge carriers in different temperature ranges were calculated. It was found that three clearly defined temperature ranges with different activation energies can be distinguished, which is associated with the different nature of charge carriers in the studied solid solutions of the perovskite type. The effect of substitution of Nd3+ ions for Bi3+ ions is investigated.The electrophysical and structural characteristics of bismuth titanate oxides of a number of phases of solid solutions of the Aurivillius phases Bi7−2xNd2xTi4NbO21 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) having a layered structure of the perovskite type have been investigated. According to the XRD data, all studied compounds are single-phase and have a mixed-layer structure of Aurivillius phases (m = 2.5) with a rhombic crystal lattice (space group I2cm, Z = 2). A relationship has been established between changes in the chemical composition of solid solutions and orthorhombic and tetragonal distortions of perovskite-like layers. The temperature dependences of the relative permittivity 𝜀/𝜀o(T) are measured. It was found that the change in the phase transition temperature — Curie temperature TC synthesized Aurivillius phases Bi7−xNd2xTi4NbO21 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) has a close to linear dependence on the change in the parameter x. The activation energies of charge carriers in different temperature ranges were calculated. It was found that three clearly defined temperature ranges with different activation energies can be distinguished, which is associated with the different nature of charge carriers in the studied solid solutions of the perovskite type. The effect of substitution of Nd3+ ions for Bi3+ ions is investigated.

The Aurivillius phases [Bi2O2][An−1BnO3n+1] are well-known ferroelectrics with high Curie temperatures TC. High-temperature piezoceramics Bi3−xGdxTiTaO9 (BGdTTa, x= 0.0, 0.1, 0.2, 0.3) were prepared by a solid-state reaction method. The structural and electrophysical characteristics of BGdTTa ceramics have been studied. According to the data of powder X-ray diffraction, all the compounds are single-phase with the structures of two-layer Aurivillius phases (m = 2) with the orthorhombic crystal lattice (space group A21am). The temperature dependence of the relative permittivity 𝜀/𝜀0 (T) of the compounds was measured and showed that the Curie temperature TC of perovskite-like oxides Bi3−xGdxTiTaO9 increases linearly with an increase in the substitution parameter x to TC = 925∘C. The activation energies of charge carriers have been found in different temperature ranges.The Aurivillius phases [Bi2O2][An−1BnO3n+1] are well-known ferroelectrics with high Curie temperatures TC. High-temperature piezoceramics Bi3−xGdxTiTaO9 (BGdTTa, x= 0.0, 0.1, 0.2, 0.3) were prepared by a solid-state reaction method. The structural and electrophysical characteristics of BGdTTa ceramics have been studied. According to the data of powder X-ray diffraction, all the compounds are single-phase with the structures of two-layer Aurivillius phases (m = 2) with the orthorhombic crystal lattice (space group A21am). The temperature dependence of the relative permittivity 𝜀/𝜀0 (T) of the compounds was measured and showed that the Curie temperature TC of perovskite-like oxides Bi3−xGdxTiTaO9 increases linearly with an increase in the substitution parameter x to TC = 925∘C. The activation energies of charge carriers have been found in different temperature ranges.

This work presents the results of study of the electrophysical properties of composite polymer ceramics (1?x)[KNN-LTSN]–xPVDF at x = 25 vol.% and x= 50 vol.% in the temperature range of T = 20–160°C and frequency range of f = 2 × 101–2 × 106 Hz. The concentration dependence of piezomodules of the studied materials has been analyzed as a function of temperature. X-ray measurements have also been carried out. A model of description of revealed dielectric parameters dispersion in the material is presented. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity has been used to describe the temperature–frequency properties. It is shown that the dielectric spectra of the studied composites include three relaxation processes in the temperature ranges of 40–80°C, 80–120°C and 120–150 °C, which were confirmed by the dynamics of changes in the dependences of γ′(f), tgδ(f), M′(f), M′′(f) and M′′(M′). All three processes are almost exactly described by this model and well correlated with the studies by other researchers of the composites based on PVDF. The results of this work show that the use of such experimental model is suitable for describing the complex dielectric spectra of any nonlinear dielectrics including composite materials.This work presents the results of study of the electrophysical properties of composite polymer ceramics (1?x)[KNN-LTSN]–xPVDF at x = 25 vol.% and x= 50 vol.% in the temperature range of T = 20–160°C and frequency range of f = 2 × 101–2 × 106 Hz. The concentration dependence of piezomodules of the studied materials has been analyzed as a function of temperature. X-ray measurements have also been carried out. A model of description of revealed dielectric parameters dispersion in the material is presented. The nonclassical modified Havriliak–Negami model written for complex electrical conductivity has been used to describe the temperature–frequency properties. It is shown that the dielectric spectra of the studied composites include three relaxation processes in the temperature ranges of 40–80°C, 80–120°C and 120–150 °C, which were confirmed by the dynamics of changes in the dependences of γ′(f), tgδ(f), M′(f), M′′(f) and M′′(M′). All three processes are almost exactly described by this model and well correlated with the studies by other researchers of the composites based on PVDF. The results of this work show that the use of such experimental model is suitable for describing the complex dielectric spectra of any nonlinear dielectrics including composite materials.

The research findings of the phase composition, nanostructure and optical properties of strontium–barium niobate thin films are discussed. SrxBa1−xNb2O6 nanosized films (x = 0.5 and 0.61) were characterized by XRD, SEM and AFM studies. Reflective multi-angle ellipsometry and spectrophotometry were used to determine the optical parameters (refractive index, its dispersion, and thickness of the damaged surface layer) of thin films. It was shown that SBN-50 and SBN-61 thin films were grown c-oriented on Al2O3 (0001) and heteroepitaxial on MgO (001) substrates. The increase of refractive index, approaching its maximum value in the bulk material for a given composition as the film thickness increases, is observed.The research findings of the phase composition, nanostructure and optical properties of strontium–barium niobate thin films are discussed. SrxBa1−xNb2O6 nanosized films (x = 0.5 and 0.61) were characterized by XRD, SEM and AFM studies. Reflective multi-angle ellipsometry and spectrophotometry were used to determine the optical parameters (refractive index, its dispersion, and thickness of the damaged surface layer) of thin films. It was shown that SBN-50 and SBN-61 thin films were grown c-oriented on Al2O3 (0001) and heteroepitaxial on MgO (001) substrates. The increase of refractive index, approaching its maximum value in the bulk material for a given composition as the film thickness increases, is observed.

The aim of this study is to optimize the conditions for producing thin VO2 films for their use in SAW devices. We used the pulsed laser deposition (PLD) method to produce VO2 films. We used a metallic vanadium target. The dependence of the oxygen pressure during PLD on the resistive metal–insulator transition (MIT) on substrates of c-sapphire and LiNbO3 YX/128∘ was studied. The resulting films had sharp metal–insulator temperature transitions on c-Al2O3. The most high-quality films showed resistance change by four orders of magnitude. At the lower point of the hysteresis, the resistance of these samples was in the range of 50–100 Ω. The synthesized VO2 films had a sharp temperature transition and a relatively small width of thermal hysteresis. The SAW damping during its passage through a VO2/ZnO/LiNbO3 YX/128∘ film at the metal–insulator phase transition temperature was studied. Attenuation SAW decreases with increasing temperature from 52 dB/cm to 0 dB/cm.The aim of this study is to optimize the conditions for producing thin VO2 films for their use in SAW devices. We used the pulsed laser deposition (PLD) method to produce VO2 films. We used a metallic vanadium target. The dependence of the oxygen pressure during PLD on the resistive metal–insulator transition (MIT) on substrates of c-sapphire and LiNbO3 YX/128∘ was studied. The resulting films had sharp metal–insulator temperature transitions on c-Al2O3. The most high-quality films showed resistance change by four orders of magnitude. At the lower point of the hysteresis, the resistance of these samples was in the range of 50–100 Ω. The synthesized VO2 films had a sharp temperature transition and a relatively small width of thermal hysteresis. The SAW damping during its passage through a VO2/ZnO/LiNbO3 YX/128∘ film at the metal–insulator phase transition temperature was studied. Attenuation SAW decreases with increasing temperature from 52 dB/cm to 0 dB/cm.

This paper presents a numerical homogenization analysis of a porous piezoelectric composite with a partially metalized pore surface. The metal layers can be added to the pore surfaces to improve the mechanical and electromechanical properties of ordinary porous piezocomposites. Physically, constructing that composite with completely metalized pore surfaces is a challenging process, and imperfect metallization is more expected. Here, we investigate the effects of possible incomplete metallization of pore surfaces on the composite’s equivalent properties. We applied the effective moduli theory, which was developed for the piezoelectric medium based on the Hill–Mandel principle, and the finite element method to compute the effective moduli of the considered composites. Using specific algorithms and programs in the ANSYS APDL programming language, we constructed the representative unit cell element models and performed various computational experiments. Due to the presence of metal inclusion, we found that the dielectric and piezoelectric properties of the considered composites differ dramatically from the corresponding properties of the ordinary porous piezocomposites. The results of this work showed that piezocomposites with partially metallized pore surfaces can have a higher anisotropy, compared to the pure piezoceramic matrix, due to the defects in metal coatings.This paper presents a numerical homogenization analysis of a porous piezoelectric composite with a partially metalized pore surface. The metal layers can be added to the pore surfaces to improve the mechanical and electromechanical properties of ordinary porous piezocomposites. Physically, constructing that composite with completely metalized pore surfaces is a challenging process, and imperfect metallization is more expected. Here, we investigate the effects of possible incomplete metallization of pore surfaces on the composite’s equivalent properties. We applied the effective moduli theory, which was developed for the piezoelectric medium based on the Hill–Mandel principle, and the finite element method to compute the effective moduli of the considered composites. Using specific algorithms and programs in the ANSYS APDL programming language, we constructed the representative unit cell element models and performed various computational experiments. Due to the presence of metal inclusion, we found that the dielectric and piezoelectric properties of the considered composites differ dramatically from the corresponding properties of the ordinary porous piezocomposites. The results of this work showed that piezocomposites with partially metallized pore surfaces can have a higher anisotropy, compared to the pure piezoceramic matrix, due to the defects in metal coatings.

SnO2–ZnO thin films consisting of nanoscale crystallites were obtained on glass and silicon substrates by solid-phase low-temperature pyrolysis. The synthesized materials were studied by XRD and SEM methods, electrophysical and optical properties were evaluated, as well as the band gap was calculated. It was shown that regardless of the phase composition all films were optically transparent in the visible range (310–1000 nm). The nanocrystallites’ minimum size, the highest activation energy of the conductivity and the smallest band gap calculated for indirect transitions were shown for a thin film 50SnO2–50ZnO. It was assumed that the band gap decreasing might be attributed to the existence of surface electric fields with a strength higher than 4 × 105 V/cm.SnO2–ZnO thin films consisting of nanoscale crystallites were obtained on glass and silicon substrates by solid-phase low-temperature pyrolysis. The synthesized materials were studied by XRD and SEM methods, electrophysical and optical properties were evaluated, as well as the band gap was calculated. It was shown that regardless of the phase composition all films were optically transparent in the visible range (310–1000 nm). The nanocrystallites’ minimum size, the highest activation energy of the conductivity and the smallest band gap calculated for indirect transitions were shown for a thin film 50SnO2–50ZnO. It was assumed that the band gap decreasing might be attributed to the existence of surface electric fields with a strength higher than 4 × 105 V/cm.

Within the framework of the linearized theory of electroelastic wave propagation, a model of a piezoelectric structure with a prestressed functionally graded coating made of piezoceramics of a trigonal system with a symmetry class of 3m is considered. The ferroelectric LiNbO3 is used as the main material of the structure. The initial deformed state of the coating material is homogeneous, induced by the action of initial mechanical stresses and an external electrostatic field, the properties of the coating continuously change in thickness. By the example of the problem of the propagation of SH-waves from a remote source for structures with an inhomogeneous prestressed coating in the case of an electrically free and short-circuited surface, the influence of the nature and localization of the inhomogeneity of the coating on the features of SAW propagation is studied. The separate and combined effects of initial actions on changes in the physical properties of the structure, the transformation of the surface wave field, and the change in the SAW velocities in a wide frequency range is studied. The results obtained in this work are useful for understanding the dynamic processes in prestressed piezoelectric structures, in the optimization and design of new structures and devices on SAW with high performance characteristics.Within the framework of the linearized theory of electroelastic wave propagation, a model of a piezoelectric structure with a prestressed functionally graded coating made of piezoceramics of a trigonal system with a symmetry class of 3m is considered. The ferroelectric LiNbO3 is used as the main material of the structure. The initial deformed state of the coating material is homogeneous, induced by the action of initial mechanical stresses and an external electrostatic field, the properties of the coating continuously change in thickness. By the example of the problem of the propagation of SH-waves from a remote source for structures with an inhomogeneous prestressed coating in the case of an electrically free and short-circuited surface, the influence of the nature and localization of the inhomogeneity of the coating on the features of SAW propagation is studied. The separate and combined effects of initial actions on changes in the physical properties of the structure, the transformation of the surface wave field, and the change in the SAW velocities in a wide frequency range is studied. The results obtained in this work are useful for understanding the dynamic processes in prestressed piezoelectric structures, in the optimization and design of new structures and devices on SAW with high performance characteristics.

Piezoelectric properties and related figures of merit are studied in novel 1–3-type composites based on ferroelectric domain-engineered lead-free single crystal with the relatively large longitudinal piezoelectric coefficient d33. Relationships between the piezoelectric properties and the set of figures of merit are analyzed for the 1–3 and 1–3–0 composites that contain the same single-crystal and polymer components. For a composite characterized by 1–3–0 connectivity, an influence of a porous piezo-passive matrix on the figures of merit and their volume-fraction behavior is considered additionally. A large anisotropy of figures of merit is observed in the 1–3–0 composite with specific porous matrices. A diagram is put forward to show volume-fraction regions of the large anisotropy of figures of merit of the studied 1–3–0 composite. Due to large figures of merit and their considerable anisotropy, the studied lead-free composites can be applied in piezoelectric energy-harvesting systems, sensors, transducers, and so on.Piezoelectric properties and related figures of merit are studied in novel 1–3-type composites based on ferroelectric domain-engineered lead-free single crystal with the relatively large longitudinal piezoelectric coefficient d33. Relationships between the piezoelectric properties and the set of figures of merit are analyzed for the 1–3 and 1–3–0 composites that contain the same single-crystal and polymer components. For a composite characterized by 1–3–0 connectivity, an influence of a porous piezo-passive matrix on the figures of merit and their volume-fraction behavior is considered additionally. A large anisotropy of figures of merit is observed in the 1–3–0 composite with specific porous matrices. A diagram is put forward to show volume-fraction regions of the large anisotropy of figures of merit of the studied 1–3–0 composite. Due to large figures of merit and their considerable anisotropy, the studied lead-free composites can be applied in piezoelectric energy-harvesting systems, sensors, transducers, and so on.

Study of the fatigue endurance and mechanical strength of solid solutions of the PZT–PZN–PMN system, modified with Ba and Sr, corresponding to the formula (Pb1−α1−α2Srα1Baα1) [TixZry〈(Nb2/3Zn1/3) (Nb2/3Mg1/3)〉1−x−y]O3, with α1 = 0.02 ÷ 0.12; Δα1 = 0.02, α2 = 0.0036 ÷ 0.073; x= 0.385 ÷ 0.430, y= 0.402 ÷ 0.447 is presented. It is shown that the evolution of the polarization characteristics with an increase in the number of repolarization cycles, n, is characterized by two sections: slow fatigue and logarithmic evolution. It was found that an increase in the strontium content shifts the beginning of the logarithmic stage towards to the large n. It is shown that an increase in the average grain size decreases the mechanical strength. A conclusion is made about the expediency of using the obtained data in the development of devices operating in power modes.Study of the fatigue endurance and mechanical strength of solid solutions of the PZT–PZN–PMN system, modified with Ba and Sr, corresponding to the formula (Pb1−α1−α2Srα1Baα1) [TixZry〈(Nb2/3Zn1/3) (Nb2/3Mg1/3)〉1−x−y]O3, with α1 = 0.02 ÷ 0.12; Δα1 = 0.02, α2 = 0.0036 ÷ 0.073; x= 0.385 ÷ 0.430, y= 0.402 ÷ 0.447 is presented. It is shown that the evolution of the polarization characteristics with an increase in the number of repolarization cycles, n, is characterized by two sections: slow fatigue and logarithmic evolution. It was found that an increase in the strontium content shifts the beginning of the logarithmic stage towards to the large n. It is shown that an increase in the average grain size decreases the mechanical strength. A conclusion is made about the expediency of using the obtained data in the development of devices operating in power modes.

The relaxor behavior of PLZT ferroelectric ceramics has been analyzed in a wide frequency and temperature ranges, below and above the temperature for the formation of the so-called polar nano-regions (PNRs). An approximation to the dynamical behavior of the PNRs has been discussed using Cole–Cole’s relaxation model and Jonscher’s Universal Relaxation Law. The analysis considers both the dipolar contribution and those ones associated with DC and AC electric conductivities, this latter not being previously reported in the literature for relaxor materials. The effectiveness of the developed model has been verified from the agreement between the experimental data and the theoretical calculations. This study also offers an indirect method to predict the DC component of the electrical conductivity.The relaxor behavior of PLZT ferroelectric ceramics has been analyzed in a wide frequency and temperature ranges, below and above the temperature for the formation of the so-called polar nano-regions (PNRs). An approximation to the dynamical behavior of the PNRs has been discussed using Cole–Cole’s relaxation model and Jonscher’s Universal Relaxation Law. The analysis considers both the dipolar contribution and those ones associated with DC and AC electric conductivities, this latter not being previously reported in the literature for relaxor materials. The effectiveness of the developed model has been verified from the agreement between the experimental data and the theoretical calculations. This study also offers an indirect method to predict the DC component of the electrical conductivity.

BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.BiFeO3 thin films were prepared using the chemical solution route on Pt/TiO2/SiO2/Si(100) substrates under different crystallization kinetics. The crystallization kinetic effects on the dielectric and electrical properties have been investigated. These properties included dielectric permittivity, electric modulus, electrical conductivity measurements as a function of the temperature (300–525 K) and frequency (102–106 Hz), and leakage current measurements electric field range ± 30 kV/cm at room temperature. The differences observed in conductivity and current density of the BiFeO3 films were discussed in terms of possible defects induced by the crystallization kinetic. An anomalous relaxor-like dielectric behavior characterized by a broad maximum in the real dielectric permittivity as a function of temperature and the low-frequency dielectric dispersion has been observed. The nonexpected peaks in the real permittivity were accompanied by increasing at least four orders in the conductivity’s magnitude at high temperatures. The origin of the relaxor-like dielectric anomalies is discussed, suggesting that the dielectric permittivity peaks are artifacts due to carrier migration correlated to the onset of the Maxwell–Wagner effect.

(1–x)Bi0.5Na0.5TiO3–xBaTiO3lead-free ceramics have been obtained from the conventional solid-state reaction sintering method. The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques. Results revealed well-crystallized ceramic samples with perovskite structure. Microstructural properties, obtained from scanning electron microscopy measurements, have shown high density with very low porosity level. The dielectric response, analyzed as a function of the temperature and several frequencies, showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system. Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.(1–x)Bi0.5Na0.5TiO3–xBaTiO3lead-free ceramics have been obtained from the conventional solid-state reaction sintering method. The structural properties were investigated from X-ray diffraction and Raman spectroscopy techniques. Results revealed well-crystallized ceramic samples with perovskite structure. Microstructural properties, obtained from scanning electron microscopy measurements, have shown high density with very low porosity level. The dielectric response, analyzed as a function of the temperature and several frequencies, showed very broad peaks with a strong frequency dependence of the temperature for the maximum dielectric permittivity for the modified system. Results were analyzed considering the influence of the BaTiO3 content on the studied physical properties.

Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, 𝜀(E), which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90∘ and 180∘ domains walls.Electromechanical and dielectric properties of PMN–PT ferroelectric ceramics are investigated. In particular, dielectric response studies focus on the investigation of the influence of the DC applied electric field on the dielectric permittivity as a function of temperature and frequency. Results reveal an electric field driven dielectric anomaly in the dielectric permittivity curves, 𝜀(E), which in turn prevails in the whole ferroelectric phase region and continuously vanishes for temperatures near the paraelectric-ferroelectric phase transition temperature. A schematic model for the domains dynamics of the studied material is proposed taking into account the simultaneous contribution of both 90∘ and 180∘ domains walls.

Doping effects of CuO on the sintering behavior and electrical properties of 0.94(Bi0.5Na0.5)TiO3–0.06(BaTiO3)–xCuO (BNT–BT6–xCu) lead-free piezoceramic obtained by the conventional solid-state reaction method were investigated. Regarding the undoped system, it is already known that it presents the best densification values when it is sintered at 1150∘C, however, the doped system was sintered at 1150∘C, 1100∘C, 1050∘C, 1025∘C, and 975∘C to determine the effect of Cu on the densification process. Therefore, it was obtained that the CuO-doped samples sintered at 1050∘C presented the highest density values and therefore were the ones chosen to perform the characterization tests together with the undoped system. The samples were characterized using X-ray diffraction (XRD), Raman microspectroscopy, and scanning electron microscopy (SEM) analysis, whereas the ferroelectric and dielectric properties were evaluated by means of ferroelectric hysteresis loops and impedance spectroscopy studies. As a result, the addition of CuO allowed an improvement in sinterability and densification, with the subsequent grain growth, and the improvement of the piezoelectric coefficient (d33).Doping effects of CuO on the sintering behavior and electrical properties of 0.94(Bi0.5Na0.5)TiO3–0.06(BaTiO3)–xCuO (BNT–BT6–xCu) lead-free piezoceramic obtained by the conventional solid-state reaction method were investigated. Regarding the undoped system, it is already known that it presents the best densification values when it is sintered at 1150∘C, however, the doped system was sintered at 1150∘C, 1100∘C, 1050∘C, 1025∘C, and 975∘C to determine the effect of Cu on the densification process. Therefore, it was obtained that the CuO-doped samples sintered at 1050∘C presented the highest density values and therefore were the ones chosen to perform the characterization tests together with the undoped system. The samples were characterized using X-ray diffraction (XRD), Raman microspectroscopy, and scanning electron microscopy (SEM) analysis, whereas the ferroelectric and dielectric properties were evaluated by means of ferroelectric hysteresis loops and impedance spectroscopy studies. As a result, the addition of CuO allowed an improvement in sinterability and densification, with the subsequent grain growth, and the improvement of the piezoelectric coefficient (d33).

In the search for new materials with applicable magnetic properties in spintronic devices, the aim of this work is to report the synthesis of the lanthanide ferrocobaltite La2CoFeO6 using the modified Pechini route; the experimental study of structural, morphological and magnetic properties, and the analysis of the electronic structure and bands are obtained in the framework of the Density Functional Theory. Rietveld refinement of experimental X-ray diffraction patterns revealed the crystallization of this oxide material in a perovskite-like monoclinic structure, space group P21/n (# 14). Scanning electron microscopy and atomic force microscopy images revealed that the surface morphology is essentially polycrystalline, with mean grain sizes between 177 and 188 nm. The dispersive X-ray spectroscopy suggests that the material obtained contains La, Fe, Co and O in the stoichiometric proportions expected by up to 98%. The magnetic susceptibility curves as a function of temperature indicated that the material is ordered ferromagnetically, showing strong irreversibility effects due to the disorder of the Fe and Co cations in the three crystallographic directions of the structure and to the strong distortions in the FeO6 and CoO6 octahedra. Magnetic hysteresis curves confirmed the ferromagnetic character of the material for all temperatures evaluated, up to room temperature. I–V response curves revealed a semiconductor-like behavior with a figure of merit exponent 1.53 of the varistor type. The ferromagnetic semiconductor behavior suggests the potential applicability of the material in spintronic technological devices.In the search for new materials with applicable magnetic properties in spintronic devices, the aim of this work is to report the synthesis of the lanthanide ferrocobaltite La2CoFeO6 using the modified Pechini route; the experimental study of structural, morphological and magnetic properties, and the analysis of the electronic structure and bands are obtained in the framework of the Density Functional Theory. Rietveld refinement of experimental X-ray diffraction patterns revealed the crystallization of this oxide material in a perovskite-like monoclinic structure, space group P21/n (# 14). Scanning electron microscopy and atomic force microscopy images revealed that the surface morphology is essentially polycrystalline, with mean grain sizes between 177 and 188 nm. The dispersive X-ray spectroscopy suggests that the material obtained contains La, Fe, Co and O in the stoichiometric proportions expected by up to 98%. The magnetic susceptibility curves as a function of temperature indicated that the material is ordered ferromagnetically, showing strong irreversibility effects due to the disorder of the Fe and Co cations in the three crystallographic directions of the structure and to the strong distortions in the FeO6 and CoO6 octahedra. Magnetic hysteresis curves confirmed the ferromagnetic character of the material for all temperatures evaluated, up to room temperature. I–V response curves revealed a semiconductor-like behavior with a figure of merit exponent 1.53 of the varistor type. The ferromagnetic semiconductor behavior suggests the potential applicability of the material in spintronic technological devices.

The effect of sintering condition on structure, microstructure, and ferroelectric properties of (K0.44Na0.52Li0.04) (Nb0.86Ta0.10Sb0.04)- O3 (KNL–NTS) has been investigated. Ceramic powders have been synthesized by the solid-state reaction method and sintered at different temperatures (1115∘C, 1125∘C, and 1140∘C). Then, samples were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. Through XRD results, the perovskite structure and small peaks corresponding to a secondary phase were detected. Ceramics processed at the highest temperatures showed higher densities and good piezoelectric properties (d33, Kp, and Kt), particularly specimens sintered at 1125∘C presented the highest piezoelectric performance.The effect of sintering condition on structure, microstructure, and ferroelectric properties of (K0.44Na0.52Li0.04) (Nb0.86Ta0.10Sb0.04)- O3 (KNL–NTS) has been investigated. Ceramic powders have been synthesized by the solid-state reaction method and sintered at different temperatures (1115∘C, 1125∘C, and 1140∘C). Then, samples were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. Through XRD results, the perovskite structure and small peaks corresponding to a secondary phase were detected. Ceramics processed at the highest temperatures showed higher densities and good piezoelectric properties (d33, Kp, and Kt), particularly specimens sintered at 1125∘C presented the highest piezoelectric performance.

Ni0.5Co0.5Fe2O4 (NCF) powders were obtained employing two alternative synthesis routes: solid-state reaction and Pechini’s methods. The ceramic powders were pressed and sintered in the temperature range of 1100∘C to 1250∘C. Microstructural and structural properties were evaluated by SEM, XRD, and Raman spectroscopy. Magnetic hysteresis loops of sintered samples were also recorded. A secondary phase was observed in samples synthesized by Pechini’s method, whereas samples obtained by the solid-state reaction method, with the mechanochemical activation of the reagents, only produced the spinel structure. Magnetic properties of samples obtained by the solid-state method displayed higher magnetic saturations and lower coercive fields than those obtained from the Pechini’s method.Ni0.5Co0.5Fe2O4 (NCF) powders were obtained employing two alternative synthesis routes: solid-state reaction and Pechini’s methods. The ceramic powders were pressed and sintered in the temperature range of 1100∘C to 1250∘C. Microstructural and structural properties were evaluated by SEM, XRD, and Raman spectroscopy. Magnetic hysteresis loops of sintered samples were also recorded. A secondary phase was observed in samples synthesized by Pechini’s method, whereas samples obtained by the solid-state reaction method, with the mechanochemical activation of the reagents, only produced the spinel structure. Magnetic properties of samples obtained by the solid-state method displayed higher magnetic saturations and lower coercive fields than those obtained from the Pechini’s method.

BaTiO3 nanoparticles were synthesized by hydrothermal method using amorphous phase TiO2 precursor as the Ti-source. The microstructure and phase structure were determined using XRD, SEM and Raman spectroscopy analysis results. The results showed that BaTiO3 nanoparticles have tetragonal structure, average size of about 100 nm was obtained at Ba/Ti ratio of 1.5, synthesis temperature of 200∘C and reaction time of 12 h. The components of the BaTiO3 lead-free ceramic system are fabricated by conventional solid-phase reaction from the average size BaTiO3 particles about 100 nm obtained by hydrothermal process. The effects of sintering behavior on dielectric, ferroelectric and piezoelectric properties of BT high-density ceramic were studied. The BaTiO3 ceramic composition sintered at 1300∘C has a relative density of 97%, the value of the electromechanical coefficient kp = 0.40, k33 = 0.42, the large piezoelectric coefficient d33 = 300 pC/N, d31=−125 pC/N.BaTiO3 nanoparticles were synthesized by hydrothermal method using amorphous phase TiO2 precursor as the Ti-source. The microstructure and phase structure were determined using XRD, SEM and Raman spectroscopy analysis results. The results showed that BaTiO3 nanoparticles have tetragonal structure, average size of about 100 nm was obtained at Ba/Ti ratio of 1.5, synthesis temperature of 200∘C and reaction time of 12 h. The components of the BaTiO3 lead-free ceramic system are fabricated by conventional solid-phase reaction from the average size BaTiO3 particles about 100 nm obtained by hydrothermal process. The effects of sintering behavior on dielectric, ferroelectric and piezoelectric properties of BT high-density ceramic were studied. The BaTiO3 ceramic composition sintered at 1300∘C has a relative density of 97%, the value of the electromechanical coefficient kp = 0.40, k33 = 0.42, the large piezoelectric coefficient d33 = 300 pC/N, d31=−125 pC/N.

Polycrystalline Na0.9Ba0.1Nb0.9(Sn0.5Ti0.5)0.1O3 is prepared by the solid-state reaction technique. The formation of single-phase material was confirmed by an X-ray diffraction study and it was found to be a tetragonal phase at room temperature. Nyquist plots (Z′′ versus Z′) show that the conductivity behavior is accurately represented by an equivalent circuit model which consists of a parallel combination of bulk resistance and constant phase elements (CPE). The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity σdc follows the Arrhenius relation. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (KWW), φ(t) = exp(−(t/τ)β) function and the value of the stretched exponent (β) is found to be almost independent of temperature. The near value of activation energies obtained from the analyses of modulus and conductivity data confirms that the transport is through an ion hopping mechanism dominated by the motion of the (O2−) ions in the structure of the investigated material.Polycrystalline Na0.9Ba0.1Nb0.9(Sn0.5Ti0.5)0.1O3 is prepared by the solid-state reaction technique. The formation of single-phase material was confirmed by an X-ray diffraction study and it was found to be a tetragonal phase at room temperature. Nyquist plots (Z′′ versus Z′) show that the conductivity behavior is accurately represented by an equivalent circuit model which consists of a parallel combination of bulk resistance and constant phase elements (CPE). The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The conductivity σdc follows the Arrhenius relation. The modulus plots can be characterized by the empirical Kohlrausch–Williams–Watts (KWW), φ(t) = exp(−(t/τ)β) function and the value of the stretched exponent (β) is found to be almost independent of temperature. The near value of activation energies obtained from the analyses of modulus and conductivity data confirms that the transport is through an ion hopping mechanism dominated by the motion of the (O2−) ions in the structure of the investigated material.

Dense (Na0.5K0.5)NbO3 lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure (pO2, ∼10−12 atm) atmosphere and adding LiF. All the ceramics have pure orthorhombic structure. Compared to the LiF-added (Na0.5K0.5)NbO3 ceramics sintered in air and the low pO2-sintered pure (Na0.5K0.5)NbO3 ceramics without LiF addition, the present ceramics exhibit improved piezoelectric and ferroelectric properties. The piezoelectric constant d33 is 125 pC/N, and the converse piezoelectric constant d33* is 186 pm/V. The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03, respectively. Under the measured electric field of 70 kV/cm, the remanent polarization is 25.9 μC/cm2 and the coercive field is 13.9 kV/cm. Furthermore, if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO2 atmosphere, the base metals cannot be oxidized, suggesting possibility of using base metals as electrodes.Dense (Na0.5K0.5)NbO3 lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure (pO2, ∼10−12 atm) atmosphere and adding LiF. All the ceramics have pure orthorhombic structure. Compared to the LiF-added (Na0.5K0.5)NbO3 ceramics sintered in air and the low pO2-sintered pure (Na0.5K0.5)NbO3 ceramics without LiF addition, the present ceramics exhibit improved piezoelectric and ferroelectric properties. The piezoelectric constant d33 is 125 pC/N, and the converse piezoelectric constant d33* is 186 pm/V. The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03, respectively. Under the measured electric field of 70 kV/cm, the remanent polarization is 25.9 μC/cm2 and the coercive field is 13.9 kV/cm. Furthermore, if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO2 atmosphere, the base metals cannot be oxidized, suggesting possibility of using base metals as electrodes.

This work outlines the characterization of epoxy resin [Bisphenol A-(epichlorhydrin): epoxy] and hardener [N(3-dimethylaminopropyl)-1,3-propylenediamine] with various inorganic nano-fillers. Dielectric characterizations of epoxy, hardener, neat epoxy (epoxy + hardener) and nano-epoxy (nano-filler + neat epoxy) composites loaded with 1 wt.% of inorganic nano-fillers (SiO2, Al2O3, TiO2 and ZnO) were carried out using precision LCR meter, over the frequency range of 1 kHz–2 MHz at a constant temperature of 300.15 K. The structural information of nano-fillers, neat epoxy and nano-epoxy composites was understood by Fourier transform infrared spectroscopy and by XRD. Moreover, hardness and shear strength (shear punch) were also determined in order to gain additional information about the mechanical properties of epoxy composite. Influence of inorganic nano-fillers on the dielectric properties, structural chemistry and mechanical properties of neat epoxy composite is discussed thoroughly in this study.This work outlines the characterization of epoxy resin [Bisphenol A-(epichlorhydrin): epoxy] and hardener [N(3-dimethylaminopropyl)-1,3-propylenediamine] with various inorganic nano-fillers. Dielectric characterizations of epoxy, hardener, neat epoxy (epoxy + hardener) and nano-epoxy (nano-filler + neat epoxy) composites loaded with 1 wt.% of inorganic nano-fillers (SiO2, Al2O3, TiO2 and ZnO) were carried out using precision LCR meter, over the frequency range of 1 kHz–2 MHz at a constant temperature of 300.15 K. The structural information of nano-fillers, neat epoxy and nano-epoxy composites was understood by Fourier transform infrared spectroscopy and by XRD. Moreover, hardness and shear strength (shear punch) were also determined in order to gain additional information about the mechanical properties of epoxy composite. Influence of inorganic nano-fillers on the dielectric properties, structural chemistry and mechanical properties of neat epoxy composite is discussed thoroughly in this study.

Effective piezoelectric properties, electromechanical coupling factors (ECF) and figures of merit (FOM) are studied in lead-free 0–3-type composites based on novel ferroelectric 0.965(K0.48Na0.52)(Nb0.96Sb0.04)O3–0.035Bi0.5Na0.5Zr0.15Hf0.75O3 ceramic. Systems of prolate ceramic inclusions are surrounded by a large polymer matrix that can be either monolithic (in the 0–3 composite) or porous (in the 0–3–0 composite). Non-monotonic volume-fraction dependences of the effective piezoelectric coefficients g3j∗, ECF k3j∗, squared FOM d3j∗g3j∗ and their modified analogs for stress-driven systems are analysed, and examples of the high longitudinal piezoelectric sensitivity (g33∗> 100 mV ⋅m/N) are considered. A role of microgeometrical factors, that promote the large effective parameters and anisotropy of properties in the 0–3-type composites, is highlighted. New “aspect ratio — volume fraction” diagrams are first built to describe conditions for high piezoelectric sensitivity, large modified FOM and their anisotropy in the studied composites. These advanced materials can be of value for piezoelectric sensor, energy-harvesting and related applications.Effective piezoelectric properties, electromechanical coupling factors (ECF) and figures of merit (FOM) are studied in lead-free 0–3-type composites based on novel ferroelectric 0.965(K0.48Na0.52)(Nb0.96Sb0.04)O3–0.035Bi0.5Na0.5Zr0.15Hf0.75O3 ceramic. Systems of prolate ceramic inclusions are surrounded by a large polymer matrix that can be either monolithic (in the 0–3 composite) or porous (in the 0–3–0 composite). Non-monotonic volume-fraction dependences of the effective piezoelectric coefficients g3j∗, ECF k3j∗, squared FOM d3j∗g3j∗ and their modified analogs for stress-driven systems are analysed, and examples of the high longitudinal piezoelectric sensitivity (g33∗> 100 mV ⋅m/N) are considered. A role of microgeometrical factors, that promote the large effective parameters and anisotropy of properties in the 0–3-type composites, is highlighted. New “aspect ratio — volume fraction” diagrams are first built to describe conditions for high piezoelectric sensitivity, large modified FOM and their anisotropy in the studied composites. These advanced materials can be of value for piezoelectric sensor, energy-harvesting and related applications.

We report the unexpectedly excellent dielectric properties of amorphous thin films with compositions in the Bi–Ti–O system. Films were deposited by RF magnetron reactive co-sputtering. In the composition range of 0.5 x Bi1−xTixOy exhibits excellent dielectric properties, with a high dielectric constant, 𝜀r∼ 53, and a dissipation factor as low as tan δ = 0.007. The corresponding maximum breakdown field reaches ∼1.6 MV/cm, yielding a maximum stored charge per unit area of up to 8 μC/cm2. This work demonstrates the potential of amorphous Bi–Ti–O as a high-performance thin-film dielectric material that is compatible with high-performance integrated circuits.We report the unexpectedly excellent dielectric properties of amorphous thin films with compositions in the Bi–Ti–O system. Films were deposited by RF magnetron reactive co-sputtering. In the composition range of 0.5 x Bi1−xTixOy exhibits excellent dielectric properties, with a high dielectric constant, 𝜀r∼ 53, and a dissipation factor as low as tan δ = 0.007. The corresponding maximum breakdown field reaches ∼1.6 MV/cm, yielding a maximum stored charge per unit area of up to 8 μC/cm2. This work demonstrates the potential of amorphous Bi–Ti–O as a high-performance thin-film dielectric material that is compatible with high-performance integrated circuits.

In order to combine the properties of inorganic ion exchanger and conducting organic polymer, a new class of organic–inorganic composite cation exchanger PANI–Ti(IV) phosphosulphosalicylate (PTPSS) was synthesized by intercalating polyaniline (PANI) into Ti(IV) phosphosulphosalicylate (Ti(IV) PSS) using sol–gel chemical route with enhanced properties. PTPSS has been characterized by using Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDAX), thermo gravimetric analysis (TGA-DTG), and Transmission Electron Microscopy (TEM). Ac electrical conductivity studies were also performed. This material possessed electrical conductivity of 10−3 – 10−6Scm−1which falls in the semiconducting range. The frequency (2 × 105 – 1 × 106 Hz) dependent Ac conductivity at room temperature suggests the evidence for the transport mechanism for the conductivity in PTPSS. The structure of the composite cation exchanger extremely supports its conducting behavior.In order to combine the properties of inorganic ion exchanger and conducting organic polymer, a new class of organic–inorganic composite cation exchanger PANI–Ti(IV) phosphosulphosalicylate (PTPSS) was synthesized by intercalating polyaniline (PANI) into Ti(IV) phosphosulphosalicylate (Ti(IV) PSS) using sol–gel chemical route with enhanced properties. PTPSS has been characterized by using Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray (EDAX), thermo gravimetric analysis (TGA-DTG), and Transmission Electron Microscopy (TEM). Ac electrical conductivity studies were also performed. This material possessed electrical conductivity of 10−3 – 10−6Scm−1which falls in the semiconducting range. The frequency (2 × 105 – 1 × 106 Hz) dependent Ac conductivity at room temperature suggests the evidence for the transport mechanism for the conductivity in PTPSS. The structure of the composite cation exchanger extremely supports its conducting behavior.

(YxBi1−x)2/3Cu3Ti4O12 (x= 0.00–0.30) ceramics were successfully prepared via the conventional solid-state method. X-ray powder diffraction confirmed the lattice constant gradually decreases with increasing Y3+ content. SEM images displayed Y3+ substitution for Bi3+ gave rise to the large abnormal grains, and the size of abnormal grains became larger with the increase of Y3+ substitution. (YxBi1−x)2/3Cu3Ti4O12 ceramics presented the relatively high dielectric constant of 7400 with the dielectric loss of 0.055 when x= 0.20. The analysis of complex impedance suggested the grains are semiconductive and the grain boundaries are insulating. For pure Bi2/3Cu3Ti4O12 ceramics, the appearance of additional low-frequency peaks in electrical modulus indicated the grain boundaries are heterogeneous. The investigation of modulus peaks fitting with Arrhenius formula implied that the low-frequency permittivity for all (YxBi1−x)2/3Cu3Ti4O12 ceramics was ascribed to the Maxwell–Wagner relaxation at grain boundaries. In addition, a set of clear dielectric peaks above 200∘C associated with Maxwell–Wagner relaxation can be found for all (YxBi1−x)2/3Cu3Ti4O12 ceramics in the temperature dependence of dielectric constant. This set of clear dielectric peaks showed a tendency to shift to higher temperatures with the increase of Y3+ substitution. Meanwhile, a tiny dielectric anomaly at room temperature was found in Y-doped Bi2/3Cu3Ti4O12 ceramics.(YxBi1−x)2/3Cu3Ti4O12 (x= 0.00–0.30) ceramics were successfully prepared via the conventional solid-state method. X-ray powder diffraction confirmed the lattice constant gradually decreases with increasing Y3+ content. SEM images displayed Y3+ substitution for Bi3+ gave rise to the large abnormal grains, and the size of abnormal grains became larger with the increase of Y3+ substitution. (YxBi1−x)2/3Cu3Ti4O12 ceramics presented the relatively high dielectric constant of 7400 with the dielectric loss of 0.055 when x= 0.20. The analysis of complex impedance suggested the grains are semiconductive and the grain boundaries are insulating. For pure Bi2/3Cu3Ti4O12 ceramics, the appearance of additional low-frequency peaks in electrical modulus indicated the grain boundaries are heterogeneous. The investigation of modulus peaks fitting with Arrhenius formula implied that the low-frequency permittivity for all (YxBi1−x)2/3Cu3Ti4O12 ceramics was ascribed to the Maxwell–Wagner relaxation at grain boundaries. In addition, a set of clear dielectric peaks above 200∘C associated with Maxwell–Wagner relaxation can be found for all (YxBi1−x)2/3Cu3Ti4O12 ceramics in the temperature dependence of dielectric constant. This set of clear dielectric peaks showed a tendency to shift to higher temperatures with the increase of Y3+ substitution. Meanwhile, a tiny dielectric anomaly at room temperature was found in Y-doped Bi2/3Cu3Ti4O12 ceramics.

The article presents the results of research the pre-transitional features of the behavior of solid solutions based on lead zirconate-titanate. The presence of a “special” critical temperature Td on the temperature dependences of the permittivity 𝜀(T) and the remanent polarization Pr(T), preceding the temperature of the paraelectric phase transition at the Curie temperature TC, is noted. In the temperature range T Td, the Pr(T) dependence obeys a power law. In the temperature range TdTTC, this law is not fulfilled. The results of X-ray experiments make it possible to associate this behavior with reversible disordering at TTd of an ordered domain structure formed during the polarization of piezoelectric ceramics and with its irreversible disordering in the temperature range TdTTC. This is due to the appearance of internal mechanical stresses in a polycrystalline ferroelectric due to irreversible depolarization of the samples at temperatures TdTTC.The article presents the results of research the pre-transitional features of the behavior of solid solutions based on lead zirconate-titanate. The presence of a “special” critical temperature Td on the temperature dependences of the permittivity 𝜀(T) and the remanent polarization Pr(T), preceding the temperature of the paraelectric phase transition at the Curie temperature TC, is noted. In the temperature range T Td, the Pr(T) dependence obeys a power law. In the temperature range TdTTC, this law is not fulfilled. The results of X-ray experiments make it possible to associate this behavior with reversible disordering at TTd of an ordered domain structure formed during the polarization of piezoelectric ceramics and with its irreversible disordering in the temperature range TdTTC. This is due to the appearance of internal mechanical stresses in a polycrystalline ferroelectric due to irreversible depolarization of the samples at temperatures TdTTC.

Bis-Tetrapropylammonium tetrabromozincate was synthesized and characterized by X-ray powder diffraction, as well as vibrational and impedance spectroscopy. Rietveld’s refinement of X-ray diffractogram confirmed the crystallization of the compound through the monoclinic system (space group C2/c). A temperature study of Raman scattering revealed two phase transitions at approximately T1 = 340 K and T2 = 393 K. The wavenumber and the line width’s evolution as a function of temperature showed some peculiarities associated with these transitions, which suggests that they are governed by the reorientation of the organic part [N(C3H7)4]+. The complex impedance plotted as a double semicircular arc in the studied temperature range and the centers of these semicircles lie below the real axis, which indicates that the material is an on-Debye type. These semicircular arcs are related to the bulk and the grain boundary effects. Furthermore, the alternating current conductivity of [N(C3H7)4]2ZnBr4 obeyed Jonscher’s law: σAC(ω) = σdc+Aωs and the conduction could be attributed to the correlated barrier hopping (CBH) model in both region(I) and (II) and the Non-overlapping Small Polaron Tunneling (NSPT) in region (III).Bis-Tetrapropylammonium tetrabromozincate was synthesized and characterized by X-ray powder diffraction, as well as vibrational and impedance spectroscopy. Rietveld’s refinement of X-ray diffractogram confirmed the crystallization of the compound through the monoclinic system (space group C2/c). A temperature study of Raman scattering revealed two phase transitions at approximately T1 = 340 K and T2 = 393 K. The wavenumber and the line width’s evolution as a function of temperature showed some peculiarities associated with these transitions, which suggests that they are governed by the reorientation of the organic part [N(C3H7)4]+. The complex impedance plotted as a double semicircular arc in the studied temperature range and the centers of these semicircles lie below the real axis, which indicates that the material is an on-Debye type. These semicircular arcs are related to the bulk and the grain boundary effects. Furthermore, the alternating current conductivity of [N(C3H7)4]2ZnBr4 obeyed Jonscher’s law: σAC(ω) = σdc+Aωs and the conduction could be attributed to the correlated barrier hopping (CBH) model in both region(I) and (II) and the Non-overlapping Small Polaron Tunneling (NSPT) in region (III).

The coming Big Data Era requires progress in storage and computing technologies. As an emerging memory technology, Resistive RAM (RRAM) has shown its potential in the next generation high-density storage and neuromorphic computing applications, which extremely demand low switching voltage and power consumption. In this work, a 10 nm-thick amorphous GeS2 thin film was utilized as the functional layer of RRAM in a combination with Ag and Pt electrodes. The structure and memory performance of the GeS2-based RRAM device was characterized — it presents high on/off ratio, fast switching time, ultralow switching voltage (0.15 V) and power consumption (1.0 pJ and 0.56 pJ for PROGRAM and ERASE operations, respectively). We attribute these competitive memory characteristics to Ag doping phenomena and subsequent formation of Ag nano-islands in the functional layer that occurs due to diffusion of Ag from electrode into the GeS2 thin film. These properties enable applications of GeS2 for low energy RRAM device.The coming Big Data Era requires progress in storage and computing technologies. As an emerging memory technology, Resistive RAM (RRAM) has shown its potential in the next generation high-density storage and neuromorphic computing applications, which extremely demand low switching voltage and power consumption. In this work, a 10 nm-thick amorphous GeS2 thin film was utilized as the functional layer of RRAM in a combination with Ag and Pt electrodes. The structure and memory performance of the GeS2-based RRAM device was characterized — it presents high on/off ratio, fast switching time, ultralow switching voltage (0.15 V) and power consumption (1.0 pJ and 0.56 pJ for PROGRAM and ERASE operations, respectively). We attribute these competitive memory characteristics to Ag doping phenomena and subsequent formation of Ag nano-islands in the functional layer that occurs due to diffusion of Ag from electrode into the GeS2 thin film. These properties enable applications of GeS2 for low energy RRAM device.

Structural and dielectric properties of Ce-doped BaTi0.97Y0.03O3 powders, with the chemical formulation (Ba1−xCex)(Ti(0.97−x/4)- Y0.03)O3 such as x = 0%, 1%, 3%, 5%, 7% and 9%, produced by the sol–gel method, have been investigated. X-ray diffraction analysis showed that Ce3+ ions incorporated Ba sites until x= 7% indicating that this concentration represents a solubility limit of Ce3+ ions in BaTi0.97Y0.03O3 matrix. Scanning electron microscopy (SEM) analysis showed a decrease in grain size down to the same concentration of 7%. Raman spectroscopy analysis showed the appearance of A1g mode, which we attributed to the effect of incorporation of Ce3+ and Y3+ in BaTiO3 matrix. Dielectric measurements revealed that doping with cerium lowers the temperature of permittivity maximum at the ferroelectric-to-paraelectric transition (FPT) of the BaTi0.97Y0.03O3 sample, and reaches a value that should be below 40∘C for x= 9%. Moreover, the phenomenon of dielectric resonance was observed on all Ce-doped samples, which was not the case with other dopants as reported in the literature.Structural and dielectric properties of Ce-doped BaTi0.97Y0.03O3 powders, with the chemical formulation (Ba1−xCex)(Ti(0.97−x/4)- Y0.03)O3 such as x = 0%, 1%, 3%, 5%, 7% and 9%, produced by the sol–gel method, have been investigated. X-ray diffraction analysis showed that Ce3+ ions incorporated Ba sites until x= 7% indicating that this concentration represents a solubility limit of Ce3+ ions in BaTi0.97Y0.03O3 matrix. Scanning electron microscopy (SEM) analysis showed a decrease in grain size down to the same concentration of 7%. Raman spectroscopy analysis showed the appearance of A1g mode, which we attributed to the effect of incorporation of Ce3+ and Y3+ in BaTiO3 matrix. Dielectric measurements revealed that doping with cerium lowers the temperature of permittivity maximum at the ferroelectric-to-paraelectric transition (FPT) of the BaTi0.97Y0.03O3 sample, and reaches a value that should be below 40∘C for x= 9%. Moreover, the phenomenon of dielectric resonance was observed on all Ce-doped samples, which was not the case with other dopants as reported in the literature.

Thin films of polycrystalline (Ba1−xSrx)TiO3 (x = 0.2 and 0.3) with Perovskite structure were prepared by a dip and dry technique on a platinum-coated silicon substrate. The good quality thin films with uniform microstructure and thickness were successfully produced by dip-coating techniques annealed at 730∘C for 1 h. The resulting thin film shows a well-developed dense polycrystalline structure with more uniform grain size distribution. The BST thin films were characterized for their structural, Raman spectroscopy, morphological properties, and complex impedance properties. The dielectric constant-frequency curve showed the good dielectric constant and loss dielectric loss with low-frequency dispersion. The BST 0.3 thin film reveals that the dielectric constant and dielectric loss at a frequency of 1 kHz were 578 and 0.02, respectively. The obtained results on dielectric properties can be analyzed in terms of the Maxwell–Wagner model.Thin films of polycrystalline (Ba1−xSrx)TiO3 (x = 0.2 and 0.3) with Perovskite structure were prepared by a dip and dry technique on a platinum-coated silicon substrate. The good quality thin films with uniform microstructure and thickness were successfully produced by dip-coating techniques annealed at 730∘C for 1 h. The resulting thin film shows a well-developed dense polycrystalline structure with more uniform grain size distribution. The BST thin films were characterized for their structural, Raman spectroscopy, morphological properties, and complex impedance properties. The dielectric constant-frequency curve showed the good dielectric constant and loss dielectric loss with low-frequency dispersion. The BST 0.3 thin film reveals that the dielectric constant and dielectric loss at a frequency of 1 kHz were 578 and 0.02, respectively. The obtained results on dielectric properties can be analyzed in terms of the Maxwell–Wagner model.

In this study, carbon black (CB) powder-loaded polyurethane (PU) composites (CB–PU composites) were prepared by melt mixing method with different volume percentages (45, 50, 55, 58 and 61 vol.%) of CB in the PU matrix. The prepared CB–PU composites had been further studied for surface morphology using the field-emission scanning electron microscopy (FESEM) technique. Dielectric properties in terms of real permittivity (𝜀′) and imaginary permittivity (𝜀′′) of the fabricated composites were computed using an Agilent E8364B vector network analyzer in the frequency range of 8–12 GHz (X-band). Dielectric loss factor of the prepared CB–PU composites was computed in terms of the dielectric loss tangent (tan δe = 𝜀′′/𝜀′). Microwave absorbing properties were appraised in terms of the reflection loss (RL) which in turn was calculated for varying thicknesses of the prepared composites from the measured real and imaginary permittivity data. The minimum RL was observed as −20.10 dB for the absorber with a thickness of 2.2 mm and the bandwidth achieved was 1.92 GHz for RL ≤−10 dB. Based on the above results these CB–PU composites have potential use as effective microwave absorbers in 8–12-GHz (X-band) frequency range.In this study, carbon black (CB) powder-loaded polyurethane (PU) composites (CB–PU composites) were prepared by melt mixing method with different volume percentages (45, 50, 55, 58 and 61 vol.%) of CB in the PU matrix. The prepared CB–PU composites had been further studied for surface morphology using the field-emission scanning electron microscopy (FESEM) technique. Dielectric properties in terms of real permittivity (𝜀′) and imaginary permittivity (𝜀′′) of the fabricated composites were computed using an Agilent E8364B vector network analyzer in the frequency range of 8–12 GHz (X-band). Dielectric loss factor of the prepared CB–PU composites was computed in terms of the dielectric loss tangent (tan δe = 𝜀′′/𝜀′). Microwave absorbing properties were appraised in terms of the reflection loss (RL) which in turn was calculated for varying thicknesses of the prepared composites from the measured real and imaginary permittivity data. The minimum RL was observed as −20.10 dB for the absorber with a thickness of 2.2 mm and the bandwidth achieved was 1.92 GHz for RL ≤−10 dB. Based on the above results these CB–PU composites have potential use as effective microwave absorbers in 8–12-GHz (X-band) frequency range.