Microstructure, ferroelectric and piezoelectric properties of Bi0.5K0.5TiO3-modified BiFeO3–BaTiO3 lead-free ceramics with high Curie temperature

The effects of composition, sintering temperature and dwell time on the microstructure and electrical properties of (0.75 − x)BiFeO3–0.25BaTiO3–xBi0.5K0.5TiO3 + 1 mol% MnO2 ceramics were studied. The ceramics sintered at 1000 °C for 2 h possess a pure perovskite structure and a morphotropic phase boundary of rhombohedral and pseudocubic phases is formed at x = 0.025. The addition of Bi0.5K0.5TiO3 retards the grain growth and induces two dielectric anomalies at high temperatures (T1 ∼ 450–550 °C and T2 ∼ 700 °C, respectively). After the addition of 2.5 mol% Bi0.5K0.5TiO3, the ferroelectric and piezoelectric properties of the ceramics are improved and very high Curie temperature of 708 °C is obtained. Sintering temperature has an important influence on the microstructure and electrical properties of the ceramics. Critical sintering temperature is 970 °C. For the ceramic with x = 0.025 sintered at/above 970 °C, large grains, good densification, high resistivity and enhanced electrical properties are obtained. The weak dependences of microstructure and electrical properties on dwell time are observed for the ceramic with x = 0.025.