Enhanced electrical properties and depolarization temperature of BF-BT ceramics via Mn2+ and Sc3+ Co-doping and direct reaction sintering

Abstract

BiFeO₃-BaTiO₃ ceramics exhibit excellent thermal stability and outstanding electrical properties in the morphotropic phase boundary (MPB) region, making them a prominent focus of research of lead-free piezoelectric ceramics. However, the conventional sintering process often results in Bi volatilization and changes in the valence state of Fe ions, leading to high leakage current and difficulty in achieving a piezoelectric coefficient above 200 pC/N. In this study, we fabricated 0.7BiFeO₃-0.3BaTiO₃-0.1 mol% MnCO₃-x wt% Sc₂O₃ (BFM-BT-xSc) piezoelectric ceramics using a direct reaction sintering method. We investigated the microstructure, electrical properties, and thermal stability of the BFM-BT-xSc ceramics. Compared to single Mn²⁺ doping, the addition of Sc³⁺ significantly refined the grain size, suppressed the transition of Fe³⁺ to Fe²⁺, and reduced the concentration of oxygen vacancies, resulting in enhanced electrical properties of BFM-BT ceramics. The BFM-BT-0.2Sc ceramics exhibited excellent piezoelectric performance (d₃₃ = 208 pC/N, d₃₃ = 400 pC/N at 308 °C) and a high Curie temperature (T_c = 502 °C), with a resistivity of 1.69 × 10⁸ Ω cm at 200 °C. After optimizing the sintering temperature, the piezoelectric performance further improved, with d₃₃ reaching 228 pC/N, d₃₃ = 427 pC/N at 282 °C, and a resistivity of 5.9 × 10⁸ Ω cm at 200 °C. These findings indicate that BFM-BT-0.2Sc ceramics possess excellent high-temperature electrical properties, suggesting broad prospects for the co-doping of Mn²⁺ and Sc³⁺ in BF-BT-based piezoelectric ceramics for high-temperature applications.