(1-x)(Na0.5Bi0.5)TiO3-x(K0.5Bi0.5)TiO3 ceramics near morphotropic phase boundary: A structural and electrical study

In this work, lead-free (1-x)(Na-0.5 Bi-0.5)TiO3-x(K-0.5 Bi-0.5)TiO3 ferroelectric ceramics with the compositions (x(%)= 0; 12; 16; 17; 18; 19; 20; 30 and KBT) were obtained by solid state reaction at a particularly optimized calcination temperature (1000 degrees C/4H). A pure perovskite structure was observed for the different compositions. Effect of KBT addition on the microstructure, dielectric, ferroelectric and electrical properties at high temperature of (1-x)NBT-BT ceramics are studied using SEM, impedance analyzer and electrical characterization. X-ray diffraction and Rietveld refinement analysis of all samples reveal the presence of a biphasic region in the solid-solution series with a truly rhombohedral-tetragonal symmetry observed only at (x(%) = 16-20). Hence, Raman measurements allow us to conclude that the introduction of K+ creates a local disorder in the structure with a modification of the long-range symmetry. The temperature-dependent dielectric behavior reveals particularly large anomalies in the case of (x = 16%) due to the presence of more local disorder. The ferroelectric-antiferroelectric phase transition mechanisms are discussed to explain the nature of these anomalies. The results suggest a diffuse, probably second-order phase transition from the ferroelectric to the paraelectric phase, depending on the composition of all samples.