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-xBi(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 Bi0.5K0.5TiO3 content. Electrical properties of ceramics are significantly influenced by the Bi0.5K0.5TiO3 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 Bi0.5K0.5TiO3 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 degrees C. The piezoelectric constant d(33), the electromechanical coupling factor K-p and the dielectric constant epsilon(r) reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan E was 0.037. (c) 2007 Elsevier Ltd. All rights reserved.