Dipole pinning and quenching effects on depolarization temperature of ZnO and (Bi_0.5Na_0.5)TiO₃ ceramics composites

Abstract

Lead-free ferroelectric and piezoelectric ceramics, (Bi_0.5Na_0.5)TiO₃ [BNT] have a low depolarization temperature T_d of ∼180 °C in ordinary fired (OF) process. To solve this problem, we focused on two effects to increase T_d: compositing ZnO and the quenching effect. T_d is elevated by dipole pinning or increasing of lattice distortion, respectively. In this study, ZnO–BNT ceramics composites with controlled ZnO content (ZnO 100x, 100x = 0, 10, 20, 30, and 40 mol %) were prepared to increase T_d. To further increase the T_d, their composites were sintered through a quenching process. We examined the elevation of T_d and electrical properties of that quenched ZnO–BNT ceramics composites. As a result, the T_d of OF-ZnO100x increased by about 20 °C with increasing the compositing ZnO content. However, the T_d of quenched ZnO100x increased uniformly to 215 °C, regardless of the compositing ZnO content. This indicates that quenching is more effective than compositing ZnO in elevation of T_d. Quenching is the dominant effect that contributes to the overall ZnO–BNT ceramics composites, whereas compositing ZnO is effective in the vicinity of ZnO grains, that is, it is a local and limited effect. Therefore, the T_d of the ZnO–BNT ceramics composites could not be further increased by the quenching effect. In other words, dipole pinning and quenching were not synergistically effective.