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

Abstract The binary lead-free piezoelectric ceramics with the composition of (1 − x )Bi 0.5 Na 0.5 TiO 3 – x Bi 0.5 K 0.5 TiO 3 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 Bi 0.5 K 0.5 TiO 3 content. Electrical properties of ceramics are significantly influenced by the Bi 0.5 K 0.5 TiO 3 content. Two phase transitions at T t (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and T c (the Curie temperature) were observed in all the ceramics. Adding Bi 0.5 K 0.5 TiO 3 content caused the variations of T t and T c . 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 d 33 , the electromechanical coupling factor K p and the dielectric constant ɛ r reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037.