Correlations between structure, microstructure, density and dielectric properties of the lead-free ferroelectrics Bi0.5(Na,K)0.5TiO3

Abstract

Solid solutions of the lead-free ferroelectric oxides Bi[Formula: see text]Na[Formula: see text]TiO3 (BNT) and Bi[Formula: see text]K[Formula: see text]TiO3 (BKT), represented as ([Formula: see text])BNT–xBKT, are studied for very close compositions in the range [Formula: see text] to understand the correlation between the structure and the properties. Compositions are varied in steps of [Formula: see text] in the range [Formula: see text] and [Formula: see text] and [Formula: see text] in the range [Formula: see text], to precisely locate the structural transition as well as the morphotropic phase boundary (MPB) region and the compositional region of best performance. Rietveld refinement analysis of the powder X-ray diffraction patterns showed monoclinic phase up to x = 0.17 and a mixture of monoclinic and tetragonal phases for [Formula: see text]. Similarly, the density and the dielectric constant showed linear variation up to [Formula: see text] and a large increase above this composition, showing maximum values in the compositional range [Formula: see text], corresponding to the MPB region. Microstructural features also showed corresponding changes, indicating close relationship between the structure, microstructure and properties of the different compositions.