Lead-Free BiFeO3-BaTiO3 Ceramics with High Curie Temperature: Fine Compositional Tuning across the Phase Boundary for High Piezoelectric Charge and Strain Coefficients

BiFeO 3 -BaTiO 3 is a promising high-temperature piezoelectric ceramic that possesses both good electromechanical properties and a Curie temperature ( T C ). Here, the piezoelectric charge constants ( d 33 ) and strain coefficients ( d * 33 ) of (1 – x )BiFeO 3 - x BaTiO 3 (BF- x BT; 0.20 ≤ x ≤ 0.50) lead-free piezoelectrics were investigated at room temperature. The results showed a maximum d 33 of 225 pC/N in the BF-0.30BT ceramic and a maximum d * 33 of 405 pm/V in the BF-0.35BT ceramic, with T C s of 503 and 415 °C, respectively. To better understand the performance enhancement mechanisms, a phase diagram was established using the results of XRD, piezoresponse force microscopy, TEM, and electrical property measurements. The superb d 33 of the BF-0.30BT ceramic arose because of its location in the optimum point in the morphotropic phase boundary, low oxygen vacancy ( V O ·· ) concentration, and domain heterogeneity. The superior d * 33 of the BF-0.35BT ceramic was attributed to a weak relaxor behavior between coexisting macrodomains and polar nanoregions. The presented strategy provides guidelines for designing high-temperature BF-BT ceramics for different applications.