Perovskite/metal (Bi0.5Na0.5TiO3-BaTiO3/Ag) lead-free composite ceramics featuring enhanced depolarization temperature

The thermal stability of Bi0.5Na0.5TiO3-based piezoelectrics is one of the most critical metrics for practical applications. Finite element method (FEM) calculations estimate that incorporating Ag into the perovskite 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 (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 (Td) by introducing Ag into the representative BNT-6BT and forming perovskite/metal (BNT-6BT/100xAg) composite ceramics. Td of the composite with x = 0.06 is improved to 145 degrees C without the degradation of piezoelectric response, which is approximately 45 degrees C higher than the prototype BNT-6BT. Comparative experiments demonstrate that the increase in Td stems from the synergistic effect of residual thermal stress, colossal grain size (above 200 & mu;m), 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.