Origin of enhanced depolarization temperature in quenched Na0.5Bi0.5TiO3-BaTiO3 ceramics

Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT)-based lead-free piezoelectric ceramics have been actively studied in recent years as a potential replacement for lead-based materials in ultrasonic applications. However, its relatively low thermal depolarization temperature (T-d) is still an imperative obstacle hindering implementation in practical application. Recently, it was reported that quenching is an effective way to improve T-d of NBT-based ceramics, but the essential mechanism is still unclear. In this study, 0.94Na(0.5)Bi(0.5)TiO(3)-BaTiO3 (NBT-6BT) ceramics were quenched in air and liquid nitrogen, and then annealed in oxygen and nitrogen atmospheres to explore the origin of enhanced depolarization temperature. The results from this study correlate the enhancement of T-d to the residual stress, which induces a stable rhombohedral ferroelectric phase, thereby increasing the thermal depolarization temperature of NBT-6BT. Our results indicate that the residual stress is also an important factor influencing the electrical properties of quenched piezoelectric ceramics, which should be given more attention in future studies.