Phase transition behaviour and electromechanical properties of (Na1/2Bi1/2)TiO₃–KNbO₃lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x )(Na 1/2 Bi 1/2 )TiO 3 – x KNbO 3 (abbreviated as NBT–KN100 x , x = 0–0.12) were synthesized by the conventional ceramic sintering technique. The phase transition behaviour in NBT–KN100 x 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–KN100 x ceramics. Near MPB, the NBT–KN5 ceramics exhibit the optimum piezoelectric properties: k p = 0.22 and d 33 = 125 pC N −1 . The curves of permittivity versus temperature show that NBT–KN100 x 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 .