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

BiFeO 3 –BaTiO 3 (BF–BT) lead-free piezoelectric ceramics have high piezoelectricity and high Curie temperature ( T C ), but the mixed-valence Fe ions and Bi 3+ volatilization would promote the formation of Bi 25 FeO 40 /Bi 2 Fe 4 O 9 and oxygen vacancy, which greatly degrade the insulation properties required for polarization. In this study, it was found that the modification of BiAlO 3 (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– x BA 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– x BA ceramics, making them more suitable for high temperature applications. Graphical abstract