Structure and electrical properties of (Bi0.5Na0.5)1-x-y-zBaxSryCazTiO3 lead-free piezoelectric ceramics

Lead- free ( Bi0.5Na0.5) (1- x- y- x) Ba (x) Sr (y) Ca z TiO3 piezoelectric ceramics have been prepared by a conventional mixed oxide method, and their structural and electrical properties have been studied. The results of x- ray diffraction reveal that Ba2+, Sr2+ and Ca2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a solid solution with a single- phase perovskite structure, and a morphotropic phase boundary ( MPB) exists at x = 0.04 - 0.08, y = 0.015, z = 0.01. After the substitutions of Ba2+, Sr2+ and Ca2+, the ceramics exhibit a lower coercive field E-c and a larger remanent polarization Pr, which facilitates the poling and leads to an improvement in the piezoelectric coefficient d(33) and the planar electromechanical coupling factor kP. Also, the depolarization temperature T-d decreases, showing a strong dependence on the substitution level of Ba2+. For the ceramics with the compositions near the MPB, Pr = 44 mu Ccm(- 2), d(33) = 173 pCN(- 1), k(P) = 34% and Td = 120 degrees C. In addition, the ceramics exhibit a relaxor characteristic, which probably results from the cation disordering in the 12- fold coordination sites. 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 Td.