Structure and electrical properties of (Bi_0.5Na_0.5)_1-x-y-zBa_xSr_yCa_zTiO₃lead-free piezoelectric ceramics

Lead-free (Bi0.5Na0.5)1-x-y-xBaxSryCazTiO3piezoelectric 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 Bi0.5Na0.5TiO3lattices 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 Ecand a larger remanent polarization Pr, which facilitates the poling and leads to an improvement in the piezoelectric coefficient d33and the planar electromechanical coupling factor kP. Also, the depolarization temperature Tddecreases, showing a strong dependence on the substitution level of Ba2+. For the ceramics with the compositions near the MPB, Pr≤ 44 νC cm-2, d33≤ 173 pC N-1, kP≤ 34% and Td≤ 120 °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.