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 Bi0.5Na0.5TiO3 (BNT) and Bi0.5K0.5TiO3 (BKT), represented as (1−x)BNT–xBKT, are studied for very close compositions in the range 0≤x≤0.36 to understand the correlation between the structure and the properties. Compositions are varied in steps of Δx=0.02 in the range 0≤x≤0.1 and 0.2≤x≤0.36 and Δx=0.01 in the range 0.1≤x≤0.2, 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 x>0.17. Similarly, the density and the dielectric constant showed linear variation up to x=0.17 and a large increase above this composition, showing maximum values in the compositional range 0.22≤x≤0.26, corresponding to the MPB region. Microstructural features also showed corresponding changes, indicating close relationship between the structure, microstructure and properties of the different compositions.

Keywords

• Bismuth sodium potassium titanate
• Bi0.5Na0.5−xKxTiO3
• lead-free ferroelectrics
• morphotropic phase boundary
• structure–property correlations