Phase transition behaviour and electromechanical properties of (Na1/2Bi1/2)TiO3-KNbO3 lead-free piezoelectric ceramics

摘要

Lead-free piezoelectric ceramics (1 - x)(Na1/2Bi1/2)TiO3-xKNbO(3) (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: k(p) = 0.22 and d(33) = 125 pCN(-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 T-d. The depolarization reason is that the tetragonal nonpolar phase occurs and leads to the macro-micro domain transformation at about T-d.