Lithium-modified (K0.5Na0.5)NbO3-BiAlO3 lead-free piezoelectric ceramics with high Curie temperature

Lead-free piezoelectric ceramics based on the perovskite solid solution 0.995(K0.5Na0.5)1−xLixNbO3-0.005BiAlO3 were prepared using conventional solid-state sintering techniques. According to the analysis of X-ray diffraction patterns, a pure perovskite phase structure could be achieved in the studied composition range of 0≤x≤0.08. As the lithium content increased, the crystal structure gradually transitioned from orthorhombic to tetragonal symmetry. Furthermore, an orthorhombic-tetragonal phase boundary could be observed in ceramics with the compositions of 0.03≤x≤0.05. The ceramics with compositions close to the orthorhombic-tetragonal phase boundary exhibited enhanced piezoelectric activity, possessing the largest values of piezoelectric constant d33, and planar and thickness electromechanical coupling coefficients, of 182 pC/N, 0.375, and 0.460, respectively. Additionally, it was found that these ceramics with excellent piezoelectric properties also possessed a high Curie temperature (~ 450 °C), indicating that they would be suitable for application in elevated-temperature piezoelectric devices.