Phase Transition and Temperature Dependences of Electrical Properties of [Bi0.5(Na1-x-yKxLiy)0.5]TiO3 Ceramics

Lead-free piezoelectric ceramics [Bi 0.5 (Na 1- x - y K x Li y ) 0.5 ]TiO 3 (abbreviated BNT–BKT–BLT) were prepared by the conventional oxide method. The effects of BKT and BLT amounts on the phase transition and electrical properties were examined. BNT–BKT–BLT ceramics give good performances with piezoelectric constant d 33 =216 pC/N and planar electromechanical coupling factor k p =40.1% at 20 mol % BKT with a fixed BLT amount of 10 mol %. Also, the optimal d 33 of 173 pC/N and k p of 38.0% are obtained at 10 mol % and 7.5 mol % BLT, respectively when the BKT amount is 17.5 mol %. The addition of BKT reduces the depolarization temperature T d , however, it increases the Curie temperature T c . In contrast, T d and T c are shifted towards a higher temperature with increasing amount of BLT. BNT–BKT–BLT ceramics show typical ferroelectric features at room temperature. The addition of BKT increases the remnant polarization P r and lowers the coercive field E c significantly. The polarization–electric field ( P – E ) hysteresis loops at different temperatures reveal that the loops deform at a high temperature as a result of the phase transition from ferroelectric to antiferroelectric during the heating process, so that d 33 diminishes rapidly.