Quenching effects on piezoelectric properties and depolarization temperatures of (Bi0.5Na0.5)TiO3-based solid solution systems

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5(1− x )Li0.5 x )TiO3 and (1 − y)(Bi0.5Na0.48Li0.02)TiO3–yBaTiO3 (abbreviated as BNLT100x and BNLBT4-100y, respectively), were fabricated by a quenching procedure after sintering, and then their electrical properties were investigated with the aim of increasing their depolarization temperature T d. From the measurements by a resonance–antiresonance method, the electromechanical coupling factors k 33 of BNLT100x and BNLBT4-100y were exactly the same after the quenching treatment as compared with the nonquenched one. The T d of all BNLT100x quenched from 1100 °C reached around 240 °C, and they are almost 60 °C higher for x = 0, 0.02, 0.04, and almost 80 °C higher for x = 0.08 than those of nonquenched ceramics. We also found, from the measurement on BNLBT4-100y quenched from 1100 °C, that the T d values were enhanced to higher temperature by the quenching treatment, even in the case of rhombohedral side (100y 6), and MPB composition (100y = 6). Moreover, we confirmed that the rhombohedrality 90-α and the tetragonality c/a values were enhanced by the quenching treatment. This result revealed that, even in the tetragonal symmetry, the lattice distortion (tetragonality) could also be stabilized by the quenching treatment in BNT-based solid solution ceramics.