The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric properties is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.

Flexible ferroelectrics: High-quality ferroelectric materials, which polarize in response to an electric field, are usually oxides that crack when bent. Dong et al. found that high-quality membranes of barium titanate are surprisingly flexible and super-elastic. These films accommodate large strains through dynamic evolution of nanodomains during deformation. This discovery is important for developing more robust flexible devices. Science , this issue p. 475

Relaxor ferroelectrics are promising candidates for pulsed power dielectric capacitor applications because of their excellent energy-storage properties. Different from most relaxor ferroelectrics whose energy-storage density was improved by increasing the breakdown strength and reducing the remanent polarization, in this study, anti-ferroelectric (AFE) AgNbO₃ (AN) was used to partially substitute the relaxor ferroelectric 0.76Bi_0.5Na_0.5TiO₃–0.24SrTiO₃ (BNT–ST) of morphotropic phase boundary (MPB) composition to reduce the remanent polarization while maintaining large maximum polarization. In this way, a large recoverable energy-storage density (2.03 J cm⁻³) was obtained in the BNT–ST–5AN ceramics under lower electric field of 120 kV cm⁻¹, which is superior to other lead-free energy-storage materials under similar electric fields. Moreover, excellent temperature (25–175 °C) and frequency (1–100 Hz) stabilities are achieved. This performance demonstrates that the BNT–ST–5AN ceramics form a promising class of dielectric capacitive material for high-temperature pulsed power capacitors with large energy-storage density.

Typical lead-free energy storage systems and their performances for dielectric and multilayer capacitors over the last decade.

The $(1-x)\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_3–x\mathrm{Ba}\mathrm{Sn}{\mathrm{O}}_3$ $(0⩽x⩽0.30)$ perovskite solid solution ceramics were prepared by solid state reaction and studied by dielectric spectroscopy. The complex dielectric permittivity was measured as a function of frequency $(0.1\mathrm{Hz}–100\mathrm{kHz})$ in the temperature $\left(T\right)$ range of $123–573\mathrm{K}$ . The transition from the high-temperature paraelectric state where the dielectric constant obeys the Curie-Weiss law to the ergodic cluster state is found to occur at the same temperature of $485\mathrm{K}$ in all the compositions of $x⩾0.04$ and at lower temperatures in those with a smaller $x$ . For $0⩽x⩽x_c=0.19$ , the temperature of the dielectric peak $T_m$ , corresponding to the diffuse transition from the ergodic polar cluster state to the ferroelectric state, decreases with increasing $x$ and does not depend on frequency. The diffuseness of the peak gradually increases. For $x>x_c$ , the permittivity exhibits relaxor behavior with the frequency-dependent $T_m$ satisfying the Vogel-Fulcher law. The temperature variation of the permittivity on the high-temperature slope of the peak $(T>T_m)$ is characterized by the characteristic Lorenz-type quadratic law for relaxors, with the diffuseness increasing with the increase of $x$ . The mechanisms of the dielectric response in different parts of the phase diagram are discussed. In particular, the crossover from diffuse ferroelectric phase transition to relaxor ferroelectric behavior is attributed to the appearance at $x>x_c$ of the additional dielectric contribution arising from the flipping of the local polarization of the polar clusters. The temperature-composition phase diagram of the $\mathrm{Ba}\left({\mathrm{Ti}}_{1-x}{\mathrm{Sn}}_x\right){\mathrm{O}}_3$ system has been established, which delimits the paraelectric, ergodic polar cluster, nonergodic ferroelectric, and relaxor phases (states) and indicates the crossover from ferroelectric to relaxor behavior at $x=x_c$ .