Ferroelectric and piezoelectric properties of Bi0.5(Na0.925-x-yLi0.075KxAgy)0.5TiO3 lead-free ceramics

Lead-free ceramics Bi-0.5(Na0.925-x-yLi0.075KxAgy)(0.5)TiO3 have been prepared by an ordinary sintering technique, and their ferroelectric and piezoelectric properties have been studied. From the results of x-ray diffraction, Li+, K+ and Ag+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.15 < x < 0.25. Compared with pure Bi0.5Na0.5TiO3, the substitutions of K+ and Ag+ lower the coercive field E-c greatly and increase the remanent polarization P-r of the ceramics. Because of the MPB and low E-c, the piezoelectricity is significantly enhanced. For the ceramics with compositions near the MPB, the piezoelectric coefficient d(33) = 178-219pCN(-1), the planar electromechanical coupling factors k(P) = 35-39% and k(t) = 44-51%. Also, the depolarization temperature T-d reaches a minimum value near the MPB. The results of the ferroelectric and dielectric properties at high temperatures suggest that the ceramics may contain both the polar and non-polar regions at temperatures above T-d.