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

Abstract Lead-free piezoelectric ceramics based on the perovskite solid solution 0.995(K 0.5 Na 0.5 ) 1− x Li x NbO 3 –0.005BiAlO 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 (~ 450 °C), indicating that they would be suitable for application in elevated-temperature piezoelectric devices.