Mechanism of electrostrain enhancement in the single rhombohedral phase region of Ba(Ti_{1 – x}Zr_x)O₃ ceramics

A large electrostrain usually occurs at ferroelectric-ferroelectric phase boundaries. However, in the Ba(Ti_{1 – x}Zr_x)O₃ (BT-xZr) system prepared by the conventional solid-state reaction method, we discovered a local electrostrain maximum in the single rhombohedral phase region at the quasi-quadruple point with a composition of BT-0.12Zr that had a relatively weak temperature sensitivity below 50 °C. Mechanisms of the local electrostrain maximum in the single-phase region of the BT-xZr system were studied. The large coercive field and large domain size of BT-0.12Zr indicate that domain switching was not facilitated. Nevertheless, the large lattice distortion of BT-0.12Zr suggests a large intrinsic lattice strain, which predominantly contributed to the observed macroscopic electrostrain enhancement at the quasi-quadruple point composition in the single-phase region. Compared to nearby sample compositions, the largest lattice distortion of BT-0.12Zr was found to be correlated with the highest electrostrictive coefficient at the tricritical quasi-quadruple point, as deduced from phenomenological Landau analysis. Our work may shed light on the development of weakly temperature-dependent large electrostrain materials by identifying the tricritical quasi-quadruple point in ferroelectric phase diagrams.