Self-supporting Fe₂O₃–CeO₂ nano-heterojunction electrodes with rich oxygen vacancies present high catalytic performance for oxygen evolution reaction, where defect-engineering promotes the interfacial interaction and activates the lattice oxygens.

The piezoelectric and ferroelectric properties of $\left[{\mathrm{Bi}}_{0.5}{\left({\mathrm{Na}}_{1-x-y}{\mathrm{K}}_x{\mathrm{Li}}_y\right)}_{0.5}\right]\mathrm{Ti}{\mathrm{O}}_3$ (BNKLT-$x∕y$ ) lead-free piezoelectric ceramics were studied. The ceramics show excellent piezoelectric and ferroelectric properties, and the optimum properties measured are as follows: piezoelectric constant $d_{33}=231\mathrm{pC}∕\mathrm{N}$ , planar and thickness electromechanical coupling factors $k_{\mathrm{P}}=41.0\%$ and $k_{\mathrm{t}}=50.5\%$ , remanent polarization $P_r=40.2\mu \mathrm{C}∕{\mathrm{cm}}^2$ , and coercive field $E_c=2.47\mathrm{kV}∕\mathrm{mm}$ , respectively. Polarization versus electric $\left(P\text{-}E\right)$ hysteresis loops of the ceramics are well rectangle shaped, and the dependence of $P\text{-}E$ loops on temperature reveals that the depolarization temperature $T_d$ of BNKLT-$0.15∕0.075$ ceramics, which simultaneously have good piezoelectric properties $(d_{33}=164\mathrm{pC}∕\mathrm{N},k_{\mathrm{p}}=36.3\%,k_{\mathrm{t}}=48.6\%)$ and strong ferroelectricity $(P_r=38.8\mu \mathrm{C}∕{\mathrm{cm}}^2,E_c=3.73\mathrm{kV}∕\mathrm{mm})$ at room temperature, is about 195 °C.

In this letter the authors report the observation of double hysteresis loops in Cu-doped K0.5Na0.5NbO3 (KNN) ceramics. Unlike other ferroelectric titanates (e.g., BaTiO3), aging is not required for the ceramic to exhibit the double-loop-like characteristics. Based on the symmetry-conforming principle of point defects, it is suggested that defect dipoles are formed by the acceptor dopant ions-Cu2+ and O2− vacancies along the polarization direction after the diffuse tetragonal-orthorhombic phase transition of the ceramic. Because of the low migration rates of defects, the defect dipoles remain in the original orientation during the P-E loop measurement, providing a restoring force to reverse the switched polarization. The defect dipoles also provide “pinning” effects in the normal piezoelectric activities. As a result, the ceramic becomes “hardened,” exhibiting an extraordinarily high mechanical quality factor (2500), while the other piezoelectric properties remain reasonably good: electromechanical coupling coefficients kp=39%, kt=47%, and piezoelectric coefficient d33=82pC∕N.

A lead-free multiferroic ceramic of BiFe_0.96Sc_0.04O₃–BaTiO₃ is a type of ABO₃ perovskite structure, belonging to the R3c space group, but exhibiting poor insulation and weak multiferroicity.