Phase formation and dielectric properties of bismuth sodium titanate–potassium sodium niobate ceramics

In this work, the solid solution of (1-x)(Bi0.5Na0.5)TiO3-(x)(K0.5Na0.5)NbO3 ceramics with x = 0.00, 0.01, 0.03, 0.05, 0.07, 0.09 and 0.10 was prepared by a conventional mixed-oxide method. The structural phase formation, microstructure, dielectric properties were investigated. It was found that the BNT-KNN ceramics exhibited the perovskite structure with rhombohedral and pseudo-cubic symmetry. The microstructure showed grain shape depending upon compositions; i.e., the compositions of x < 0.05 the round shape grains were observed, while with x > 0.07 square or rectangular shape grains appeared. The addition of KNN into BNT ceramics resulted in the decrease of the phase transition temperature. More importantly, the dielectric properties also indicated the Morphotropic Phase Boundary (MPB) near the composition between x = 0.03 and x = 0.05.