Microstructure, ferro-piezoelectric and thermal stability of SiO₂ modified BiFeO₃–BaTiO₃ high temperature piezoceramics

Development of high-temperature piezoelectric sensors is of great interest for harsh environment applications. The principal challenge for piezoelectric materials is their limitation for upper working temperature due to low Curie temperature and increasing conductivity at high temperatures. The effects of SiO₂ addition on the microstructure, ferro-piezoelectric and thermal stability of 0.8BiFeO₃–0.2BaTiO₃ lead-free piezoelectric ceramics were investigated. XRD results indicated all the samples crystallized into the rhombohedrally distorted perovskite structure which was independent of the SiO₂ addition. SiO₂ could obviously inhibit the grain growth possibly due to the accumulation of SiO₂ at the grain boundary. The leakage currents of 0.8BiFeO₃–0.2BaTiO₃ piezoceramics were remarkably reduced by certain amounts of added SiO₂, facilitating the poling process, and improved their piezoelectric properties effectively. The optimal properties were obtained at the composition with 0.15 wt% SiO₂ addition which retained high transition temperature ~628 °C. The samples sintered in O₂ exhibited better thermal stability than those sintered in reduced atmospheres. Thus, SiO₂ proved to be a successful additive to improve the 0.8BiFeO₃–0.2BaTiO₃ piezoceramics for high-temperature applications, as a result of increased resistivity and enhanced piezoelectric activity.