Lead-free 0.7BiFeO3-0.3BaTiO3 high-temperature piezoelectric ceramics: Nano-BaTiO3 raw powder leading to a distinct reaction path and enhanced electrical properties

Herein, nano-BaTiO3/Bi2O3/Fe2O3 and BaCO3/TiO2/Bi2O3/Fe2O3 were respectively used to prepare 0.7BiFeO3-0.3BaTiO3 (0.7BF-0.3BT) ceramics by conventional solid-state method and clarify the reaction path, phase structure, microstructure, ferroelectric, and piezoelectric properties. 0.7BF-0.3BT ceramic using nano-BaTiO3 with cubic phase (CBT) undergoes the formation of rhombohedral α-phase (Rα) and the transition from Rα and CBT to rhombohedral β-phase (Rβ) and pseudo-cubic (PC) phases, while the counterpart using BaCO3/TiO2 directly generates Rβ and PC. Nano-BaTiO3 can decrease pores and oxygen vacancies in the resultant ceramics comparing to BaCO3/TiO2, which is due to an inhibited decomposition of Rα and a weaker reduction of Fe3+ to Fe2+, leading to increased density and reduced leakage current density. Benefitting from a proper phase ratio, increased density and reduced leakage current density, the enhanced piezoelectric properties d33 = 210 pC/N, kp = 0.34, Pr = 31.2 μC/cm2 and TC = 514 °C are obtained in 0.7BF-0.3BT ceramic using nano-BaTiO3. Our work reveals the importance of raw materials and the potential of BF-BT as a high-temperature lead-free piezoelectric ceramic material.