Relation between lattice distortion and depolarization temperature in quenched (Bi0.5Na0.5)TiO3-(Bi0.5Li0.5)TiO3-(Bi0.5K0.5)TiO3 ceramics

Lead-free piezoelectric ceramics, (1-0.04-x)(Bi0.5Na0.5)TiO3-0.04(Bi0.5Li0.5)TiO3-x(Bi0.5K0.5)TiO3 (abbreviated BNLKT4-100x), were prepared by quenching treatment after sintering, and then their electrical properties and lattice distortion were investigated for the purpose of increasing their depolarization temperature T-d. The T-d was similar to 40 degrees C higher for x = 0, 0.1, and 0.18 in the rhombohedral structure and at the morphotropic phase boundary composition (MPB), and similar to 80 degrees C higher for x = 0.3 and 0.4 in the tetragonal structure than those of normally cooled samples. The increase in Td was strongly correlated with enlargement for lattice distortion. T-d and k(33) for quenched BNLKT4-18 in MPB composition exhibited 0.59 degrees C and 223 degrees C, respectively. Both of T-d and k(33) was increased by quenching compared with previously reported values. That is, tread-off relation between T-d and k(33) was overcame. Moreover, T-d elevated above 300 degrees C for quenched BNLKT4-40 showing tetragonal phase. Therefore, we experimentally revealed a strong correlation between lattice distortion and T-d. The quenching is an effective of increasing T-d for BNLKT solidsolution systems without the deterioration of their piezoelectric properties. (C) 2019 The Japan Society of Applied Physics