Ferroelectric and piezoelectric properties of Bi0.5Na0.5TiO3–SrTiO3–Bi0.5Li0.5TiO3 lead-free ceramics

New lead-free ternary ceramics (1 − x − y)Bi0.5Na0.5TiO3–xSrTiO3–yBi0.5Li0.5TiO3 have been prepared by an ordinary sintering technique and their ferroelectric and piezoelectric properties have been studied. All the ceramics can be well-sintered at 1100 °C. The results of X-ray diffraction reveal that Li+ and Sr2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a single-phase rhombohedral perovskite structure. After the substitutions of Li+ and Sr2+, the coercive field EC decreases, the remanent polarization Pr increases, and hence the piezoelectric coefficient d33 and planar electromechanical coupling factor kp increase. For the ceramics with x = 0.13–0.15 and y = 0.10– 0.15, the piezoelectric properties become optimum, giving d33 = 127–146 pC/N and kP = 0.24–0.30. Our results also suggest that the ceramics may contain both the polar and non-polar regions near the depolarization temperature Td, which cause the polarization hysteresis loop become deformed and the ceramics become depolarized.