Structure, ferroelectric, and piezoelectric properties of (Bi 0.5Na0.5)1-x-y-z(Bi0.5K 0.5)xBaySrzTiO3 lead-free ceramics

New lead-free (Bi0.5Na0.5)1-x-y-z(Bi 0.5K0.5)xBaySrzTiO 3 ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric, and piezoelectric properties have been studied. X-ray diffraction patterns reveal that a morphotropic phase boundary (MPB) of rhombohedral and tetragonal phases is formed at 0.10≤x≤0.20, 0<y<0.04, and 0.01<z<0.03. After the partial substitutions of (Bi0.5K0.5)2+, Ba2+, and Sr 2+ for the A site (Bi0.5Na0.5)2+ ions of Bi0.5Na0.5TiO3, the coercive field Ec decreases greatly and the remnent polarization Pr increases significantly. Because of the MPB, lower Ec and higher Pr, the piezoelectricity of the ceramics is greatly improved. For the ceramics with x=0.15, y=0.02, and z=0.015, the piezoelectric properties become optimum, giving d33=203 pC/N, kp=31.4%, and k t=46.7%. The depolarization temperature Td reaches a minimum value at the MPB. Our results also suggest that the ceramics may contain both the polar and nonpolar regions near Td, which causes the polarization hysteresis loop to become deformed and the ceramics to become depolarized.Department of Applied Physic