Enhanced electromechanical properties of SrTiO₃-BiFeO₃-BaTiO₃ ceramics via relaxor behavior and phase boundary design

High temperature lead-free piezoceramics of 0.06SrTiO₃-0.94[(1-x)BaTiO₃- xBiFeO₃] were fabricated by the traditional solid state reaction method. The ceramics possess the pure perovskite structures, and a morphotropic phase boundary (MPB) with the pseudo-cubic and rhombohedral phases is observed at x = 0.55-0.71. The ceramics have the obvious relaxor behaviors as confirmed by the temperature and frequency dependent dielectric curves. The largest positive electrostrain (0.25%) under 65 kV/cm is achieved in the ceramics with x = 0.63. The ceramics with x = 0.63 also exhibit a large d₃₃* (425 pm/V) with a high curie temperature (T_C =282 °C) and a low hysteresis (43%). The improved electromechanical properties are attributed to the existence of relaxor behavior at BiFeO₃-BaTiO₃ phase boundary after doping SrTiO₃. These results demonstrate that the design of a ternary system like ST-BF-BT based ceramics with relaxor behavior and phase boundary composition provides an effective way to optimize the electrostrain behavior of high temperature lead-free ceramics.