Enhanced piezoelectric properties and thermal stability of Bi0.5Na0.5TiO3modified BiFeO3BaTiO3ceramics with morphotropic phase boundary

Morphotropic phase boundary (MPB) plays a key role in tuning piezoelectric responses of ferroelectric ceramics. Here, Bi0·5Na0·5TiO3modified BiFeO3BaTiO3ternary solid solutions of 0.7BiFeO3-(0.3-x)BaTiO3-xBi0.5Na0·5TiO3(referred to as BF-BT-xBNT, 0.00 ≤ x ≤ 0.04) were prepared for lead-free piezoelectrics. All the ceramics exhibit an MPB with coexisting rhombohedral (R) and tetragonal (T) phases, and the R/T phase ratio decreases upon increasing x. The increment of BNT promotes the grain growth, lowers the leakage current and Curie temperature (TC), and gradually drives the ferroelectric to relaxor transition. Because of the MPB with appropriate R/T phase ratio, increased grain size and density, and decreased leakage current, the well-balanced performance between d33 = 206 pC/N and TC = 488 °C is obtained in x = 0.01 case. In addition, the further enhanced in-situ d33 = 286–347 pC/N is obtained in BF-BT-xBNT ceramics along with the improved depolarization temperature Tdfrom 280 to 312 °C, showing a potential application for lead-free piezoceramics at high temperature.