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

BiFeO3-BaTiO3 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)BiFeO3-xBaTiO(3) (BF-xBT; 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-0.3513T ceramic, with T(C)s of 503 and 415 degrees 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)over dot>) 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.