Phase transition behaviour and electromechanical properties of (Na_1/2Bi_1/2)TiO₃–KNbO₃lead-free piezoelectric ceramics

Abstract

Lead-free piezoelectric ceramics (1 − x)(Na1/2Bi1/2)TiO3–xKNbO3 (abbreviated as NBT–KN100x, x = 0–0.12) were synthesized by the conventional ceramic sintering technique. The phase transition behaviour in NBT–KN100x ceramics with respect to changes in composition and temperature was investigated using x-ray diffraction analysis, dielectric and ferroelectric characterizations. At x = 0.04–0.06, the rhombohedral and pseudo-cubic morphotropic phase boundary (MPB) occurs in NBT–KN100x ceramics. Near MPB, the NBT–KN5 ceramics exhibit the optimum piezoelectric properties: kp = 0.22 and d33 = 125 pC N−1. The curves of permittivity versus temperature show that NBT–KN100x ceramics exhibit the diffuse phase transition and are characterized by a strong frequency dispersion of the permittivity. The hysteresis loops at different temperatures indicate that there is no existence of antiferroelectrics above the depolarization temperature Td. The depolarization reason is that the tetragonal nonpolar phase occurs and leads to the macro–micro domain transformation at about Td.