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

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 Delta x = 0.02 in the range 0 <= x <= 0.1 and 0.2 <= x <= 0.36 and Delta x = 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.