Structure, ferroelectric, and piezoelectric properties of (Bi_0.5Na_0.5)_1-x-y-z(Bi_0.5K_0.5)_xBa_ySr_zTiO₃lead-free ceramics

New lead-free (Bi0.5Na0.5)1-x-y-z(Bi0.5K0.5)xBaySrzTiO3ceramics 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 Sr2+for the A site (Bi0.5Na0.5)2+ions of Bi0.5Na0.5TiO3, the coercive field Ecdecreases greatly and the remnent polarization Princreases significantly. Because of the MPB, lower Ecand 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 kt=46.7%. The depolarization temperature Tdreaches 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.