Perovskite/metal (Bi_0.5Na_0.5TiO₃-BaTiO₃/Ag) lead-free composite ceramics featuring enhanced depolarization temperature

The thermal stability of Bi_0.5Na_0.5TiO₃-based piezoelectrics is one of the most critical metrics for practical applications. Finite element method (FEM) calculations estimate that incorporating Ag into the perovskite 0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃ (BNT-6BT) matrix will generate increased tensile stress during the cooling process from sintering temperatures due to the large mismatch in the thermal expansion coefficient. Thus, we propose a strategy to improve the depolarization temperature (T_d) by introducing Ag into the representative BNT-6BT and forming perovskite/metal (BNT-6BT/100xAg) composite ceramics. T_d of the composite with x = 0.06 is improved to 145 °C without the degradation of piezoelectric response, which is approximately 45 °C higher than the prototype BNT-6BT. Comparative experiments demonstrate that the increase in T_d stems from the synergistic effect of residual thermal stress, colossal grain size (above 200 μm), and oxygen vacancies. The present study provides an effective method to improve the thermal stability of BNT-based ceramics and can be also extended to other systems.