Structure and electrical properties of (1 − x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3 ceramics near morphotropic phase boundary

The binary lead-free piezoelectric ceramics with the composition of (1 − x)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3 were synthesized by conventional mixed-oxide method. The phase structure transformed from rhombohedral to tetragonal phase in the range of 0.16 ≤ x ≤ 0.20. The grain sizes varied with increasing the Bi0.5K0.5TiO3 content. Electrical properties of ceramics are significantly influenced by the Bi0.5K0.5TiO3 content. Two phase transitions at Tt (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and Tc (the Curie temperature) were observed in all the ceramics. Adding Bi0.5K0.5TiO3 content caused the variations of Tt and Tc. A diffuse character was proved by the linear fitting of the modified Curie–Weiss law. Besides, the ceramics with homogeneous microstructure and excellent electrical properties were obtained at x = 0.18 and sintered at 1170 °C. The piezoelectric constant d33, the electromechanical coupling factor Kp and the dielectric constant ɛr reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037.