Solid solutions of the lead-free ferroelectric oxides Bi 0:5 Na 0:5 TiO 3 (BNT) and Bi 0:5 K 0:5 TiO 3 (BKT), represented as (1 À x)BNTxBKT, 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 Áx ¼ 0:02 in the range 0 x 0:1 and 0:2 x 0:36 and Áx ¼ 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 ¼ 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.

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