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.

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.

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.

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.

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.

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.

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.

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.