Lead-free K0.5Na0.5NbO3–Bi0.5Li0.5ZrO3–BiAlO3 ternary ceramics: Structure and piezoelectric properties

Lead-free perovskite (0.995–x)(K0.5Na0.5)NbO3–x(Bi0.5Li0.5)ZrO3–0.005BiAlO3 ternary piezoelectric ceramics were projected and prepared by a conventional solid-state method. A research was conducted on the effects of (Bi0.5Li0.5)ZrO3 content on the structure and piezoelectric properties of the ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, a rhombohedral–orthorhombic–tetragonal phase coexistence was identified for the ceramics with 0.02 ≤ x ≤ 0.025, and a rhombohedral–tetragonal phase boundary was determined in the composition x = 0.03. Upon further increasing the (Bi0.5Li0.5)ZrO3 content, the rhombohedral–tetragonal phase boundary transformed to a single rhombohedral structure with x ≥ 0.035. An obviously improved piezoelectric activity was obtained for the ceramics with compositions in and around the rhombohedral–tetragonal phase boundary, among which the composition x = 0.025 exhibited the maximum values of piezoelectric constant d 33, and planar and thickness electromechanical coupling coefficients (k p and k t), of 252 pC/N, 0.366, and 0.466, respectively. In addition, the ceramic with x = 0.025 was found to possess a relatively high Curie temperature of 368 °C, suggesting it may have a prospect for applications at elevated ambient temperatures.