Structure and electrical properties of Bi_0.5Na_0.5TiO₃-BaTiO₃-Bi_0.5Li_0.5TiO₃lead-free piezoelectric ceramics

Lead-free ceramics (1-x-y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Li0.5TiO3have been prepared by a conventional ceramic technique, and their structure and electrical properties have been studied. The results of XRD measurement show that Ba2+and Li+diffuse into the Bi0.5Na0.5TiO3lattices to form a solid solution with a pure perovskite structure. With x increasing from 0.02 to 0.12, the ceramics transform gradually from rhombohedral phase to tetragonal phase and consequently a morphotropic phase boundary (MPB) exists at x = 0.06-0.10, while the concentration of Li+has no obvious influence on the crystal structure. The substitutions of Ba2+and (Bi0.5Li0.5)2+for (Bi0.5Na0.5)2+in the A-sites of Bi0.5Na0.5TiO3lower greatly the coercive field Ecand increase the remanent polarization Prof the ceramics. Because of the MPB and strong ferroelectricity (lower Ecand large Pr), the piezoelectricity of the ceramics is enhanced significantly. For the ceramics near the MPB (x = 0.06 and y = 0.025-0.10), piezoelectric coefficient d33= 152-208 pC/N and planar electromechanical coupling factor kP= 30.8-36.8%. The ceramics exhibit relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The depolarization temperature Tdshows a strong dependence on the concentration x of BaTiO3and reaches the lowest values near the MPB. The temperature dependences of ferroelectric and dielectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures above Td.