Structure, ferroelectric and piezoelectric properties of (Bi1−x−yNa0.925−x−yLi0.075)0.5BaxSryTiO3 lead-free piezoelectric ceramics

Lead-free multi-component ceramics (Bi1−x−yNa0.925−x−yLi0.075)0.5BaxSryTiO3 have been prepared by an ordinary sintering technique and their structure and electrical properties have been studied. All the ceramics can be well-sintered at 1100 °C. X-ray diffraction patterns shows that Li+, Ba2+ and Sr2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) is formed at 0.04 < x < 0.08. As compared to pure Bi0.5Na0.5TiO3 ceramic, the coercive field EC of the ceramics decreases greatly and the remanent polarization Pr of the ceramics increases significantly after the formation of the multi-component solid solution. Due to the MPB, lower EC and higher Pr, the piezoelectricity of the ceramics is greatly improved. For the ceramics with the compositions near the MPB (x = 0.04–0.08 and y = 0.02–0.04), piezoelectric coefficient d33 = 133–193 pC/N and planar electromechanical coupling factor kP = 16.2–32.1%. The depolarization temperature Td reaches a minimum value near the MPB. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures near/above Td.