Phase transition and temperature dependences of electrical properties of [Bi0.5Na1-x-yKxLiy)0.5]TiO3 ceramics

Lead-free piezoelectric ceramics [Bi-0.5(Na1-x-yKxLiy)0.5]TiO3 (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 d33 of 173 pC/N and kp 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, 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 anti ferroelectric during the heating process, so that d(33) diminishes rapidly.