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Structure and electrical properties of (Bi0.5Na0.5)1−x−y−z BaxSryCazTiO3 lead-free piezoelectric ceramics

Lead-free (Bi0.5Na0.5)1−x−y−xBax SryCazTiO3 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 Ec and a larger remanent polarization Pr, which facilitates the poling and leads to an improvement in the piezoelectric coefficient d33 and the planar electromechanical coupling factor kP. Also, the depolarization temperature Td decreases, showing a strong dependence on the substitution level of Ba2+. For the ceramics with the compositions near the MPB, Pr = 44 µC 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.