Optimization of calcination temperature of lead-free BiFeO3-BaTiO3 high-temperature piezoceramics

0.7BiFeO3-0.3BaTiO3+1mol% MnO2(0.7BFO-0.3BTO) ceramics were synthesized by conventional solid-state powder method under different calcination temperatures (Tcal) between 770 and 830 degrees C. The phase structure, microstructure, and ferroelectric and piezoelectric properties changed greatly depending on the applied Tcal. Benefitting from the formation of low defect levels and large grain size and an appropriate morphotropic phase boundary (MPB) with the rhombohedral-to-pseudocubic phase ratio = 49.1 : 50.9, BFO-BTO ceramics calcined at 785 degrees C showed the best ferroelectric, piezoelectric, and insulating properties (Pr = 23.1 mu C/cm2, EC = 25.8 kV/ cm, d33 = 167.8 pC/N, kp = 0.342%). Above Tcal = 800 degrees C, however, the ferroelectric and piezoelectric prop-erties deteriorated because volatilization of Bi and reduction of Fe caused a poor insulating property and high degree of chemical inhomogeneity. Moreover, the ceramics calcined at 785 degrees C showed a high Curie temperature (TC) of 509.2 degrees C and excellent thermal aging resistance of d33 up to 450 degrees C, demonstrating great potential for use in high-temperature applications.