Ferroelectric and piezoelectric properties of Bi_0.5Na_0.5TiO₃-SrTiO₃-Bi_0.5Li_0.5TiO₃lead-free ceramics

New lead-free ternary ceramics (1 - x - y)Bi0.5Na0.5TiO3-xSrTiO3-yBi0.5Li0.5TiO3have 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 Bi0.5Na0.5TiO3lattices to form a new solid solution with a single-phase rhombohedral perovskite structure. After the substitutions of Li+and Sr2+, the coercive field ECdecreases, the remanent polarization Princreases, and hence the piezoelectric coefficient d33and planar electromechanical coupling factor kpincrease. 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.