Dipole pinning and quenching effects on depolarization temperature of ZnO and (Bi0.5Na0.5)TiO3 ceramics composites

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5)TiO3 [BNT] have a low depolarization temperature Td of ∼180 °C in ordinary fired (OF) process. To solve this problem, we focused on two effects to increase Td: compositing ZnO and the quenching effect. Td 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 Td. To further increase the Td, their composites were sintered through a quenching process. We examined the elevation of Td and electrical properties of that quenched ZnO–BNT ceramics composites. As a result, the Td of OF-ZnO100x increased by about 20 °C with increasing the compositing ZnO content. However, the Td 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 Td. 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 Td 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.