Dielectric properties and depolarization temperature of Bi0.5(Na, K)0.5TiO3–BiFeO3 lead-free ceramics

The (1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiFeO3 lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The microstructure, dielectric properties, phase transition temperature and depolarization temperature of the ceramics were investigated. The phase structure of the ceramics is a pure perovskite phase at x≤0.21, and a second phase of K4Ti3O8 is observed at x>0.21. A method to obtain depolarization temperature by temperature dependence of electromechanical coupling factor kp, poling phase angle θmax has been proposed. The relation of temperature between depolarization and phase transition was studied by temperature dependence of dielectric properties. It is found that depolarization temperature is very close to the temperature of dielectric loss peak, and both temperatures are lower than that of ferroelectric to anti-ferroelectric phase transition. The depolarization temperature of the ceramics decreases linearly with the increase of BiFeO3, and first decreases and then increases with the increase of Bi0.5K0.5TiO3. The temperature of ferroelectric to anti-ferroelectric phase transition shifts insignificantly with the increase of BiFeO3.