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.

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.

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.

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.

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.

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.

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.

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.