Structure, electrical properties and depolarization temperature of (Bi_0.5Na_0.5)TiO₃-BaTiO₃lead-free piezoelectric ceramics

Lead-free ceramics (1 - x)Bi0.5Na0.5TiO3-xBaTiO3have been prepared by a conventional solid reaction method, and their structure, electrical properties and depolarization temperature have been studied. The results of X-ray diffraction reveal that Ba2+diffuse into the Bi0.5Na0.5TiO3lattices to form a solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.06 < x < 0.10. The grain size decreases with x. After the introduction of BaTiO3into Bi0.5Na0.5TiO3, the ceramics exhibit a lower coercive field Ecand a larger remanent polarization Pr. Because of the strong ferroelectricity and MPB, the ceramics with x = 0.06 exhibit optimum piezoelectric properties: d33= 155 pC/N and kP= 36.7%. The depolarization temperature Tdshows a strong compositional dependence and gives a minimum value at MPB. In addition, the ceramics exhibit 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 may suggest that the ceramics may contain both the polar and non-polar regions at temperatures above Td.