BiAlO₃-modified BiFeO₃–BaTiO₃ high Curie temperature lead-free piezoelectric ceramics with enhanced performance

BiFeO₃–BaTiO₃ (BF–BT) lead-free piezoelectric ceramics have high piezoelectricity and high Curie temperature (T _C), but the mixed-valence Fe ions and Bi³⁺ volatilization would promote the formation of Bi₂₅FeO₄₀/Bi₂Fe₄O₉ and oxygen vacancy, which greatly degrade the insulation properties required for polarization. In this study, it was found that the modification of BiAlO₃ (BA) in BF–BT ceramics could effectively solve these problems, reducing the leakage current to 1 × 10⁻⁹ A·cm⁻² and transiting the space charge-limited conduction to ohmic conduction. Because of the enhanced insulation properties and appropriate rhombohedral-pseudocubic phase ratio (C _R/C _PC), BF–BT–xBA ceramics in an optimized composition obtain enhanced piezoelectric performance: piezoelectric charge coefficient (d ₃₃) = 196 pC·N⁻¹, planar electromechanical coupling coefficient (k _p) = 31.1%, T _C = 487 °C and depolarization temperature (T _d) = 250 °C; unipolar strain (S _uni) = 0.17% and piezoelectric strain coefficient (d ₃₃^*) = 335 pm·V⁻¹ at 100 °C. Especially, d ₃₃ exceeds 283 pC·N⁻¹ at 233 °C and d ₃₃^* is 335 pm·V⁻¹ at 100 °C, showing an excellent high-temperature piezoelectricity and high depolarization temperature. The results are attributed to the domain structure of rhombohedral-pseudocubic phase coexistence and its high-temperature switching behavior. This work provides a feasible and effective approach to improve the high temperature piezoelectric properties of BF–BT–xBA ceramics, making them more suitable for high temperature applications. Graphical abstract: [Figure not available: see fulltext.].