Composite Scheme for Deferred Thermal Depolarization of Lead-Free Bi_0.5Na_0.5TiO₃-Based Piezoelectric Ceramics

The relatively low thermal depolarization temperature (T_d) has hindered the development and practical application of lead-free Bi_0.5Na_0.5TiO₃-based systems; therefore, a feasible strategy is urgently needed to defer the depolarization behavior. In this work, a perovskite/metal 0.78 Bi_0.5Na_0.5TiO₃-0.22 Bi_0.5K_0.5TiO₃/xAg (BNT-22BKT/xAg) composite ceramic is designed and successfully prepared. The introduction of metal Ag with a larger thermal expansion coefficient leads to an increased fraction and enhanced lattice distortion of the rhombohedral phase, as well as an enlarged domain size. The thermal stability thus is effectively improved, and the optimal T_d value of 166 °C is obtained at x = 0.03, which is about 60 °C higher than that of prototype ceramics. This research provides a perovskite/metal composite scheme to increase the depolarization temperature of BNT-based ceramics and promotes their potential for practical applications.