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-x)LixNbO3-005BiAlO(3) 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 d(33), 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 (similar to 450 degrees C), indicating that they would be suitable for application in elevated temperature piezoelectric devices.