Deciphering the high-temperature phase transitions and piezoelectric response in 75BiFeO3-25BaTiO3 piezoceramics

The real-time temperature-dependent piezoelectric coefficient d 33 suggests a significantly increased piezo-response below 350 °C and a wide depolarization temperature ( T d ) range of 350-525 °C for the 75BiFeO 3 -25BaTiO 3 (75BF-25BT) ceramics. By the in-situ XRD, Raman, and TEM characterization, a phase evolution from R 3 c to R 3 m and obvious domain refinement were found to occur in the temperature range of 200-300 °C. The R 3 m / P 4 mm phase coexistence associated with the thermally assisted domain motions was considered to be the main reason for the significant enhancement of d 33 below 350 °C. Furthermore, the migration of oxygen vacancies is the dominant contribution to the reduction in electrical resistivity as the temperature exceeds 350 °C, leading to a large increase in the dielectric loss. The high-temperature phase transitions, the gradual decrease in rhombohedral/tetragonal lattice distortion, and the increased leakage conduction are likely the causes of depolarization in the 75BF-25BT ceramics.