Effect of synthesis route on structure and dielectric properties of (1-x)BiFeO3-xBaTiO3 solid solutions and its phase diagram

We present here a comparative study of structure, surface morphology, composition analysis, and dielectric properties of (1-x)BiFeO3-xBaTiO3 (BF-xBT) solid solutions, synthesized by two different solid state reaction routes reported in the literature. The results of structural and dielectric studies suggest that BF-xBT ceramics synthesized using BaTiO3, Bi2O3, and Fe2O3 (method-I) as initial ingredients are not monophasic for 0.50 < x < 0.80. In this composition range, we observe the phase coexistence of tetragonal and rhombohedral/pseudocubic phases. The ferroelectric Curie temperature (TC ∼ 400 K) of this tetragonal phase corresponds to the TC of BaTiO3. Composition analysis of these ceramics also confirms the presence of BaTiO3-rich phase. These observations suggest that BaTiO3 does not react completely with Bi2O3 and Fe2O3 when synthesized by method-I. In marked contrast, the BF-xBT solid solutions synthesized by method-II using Bi2O3, Fe2O3, BaCO3, and TiO2 as initial ingredients are compositionally homogeneous and single phase in the entire composition range (0 < x ≤ 1). The average atomic percentage of Bi, Fe, Ba, and Ti for BF-xBT ceramics synthesized by method-II, as obtained from energy dispersive x-ray spectroscopy, is close to the nominal composition within ±2%. Structural and dielectric studies do not reveal any signature of the coexistence of phases in these samples. Using the results of structural and dielectric studies, we also present a new and updated phase diagram of BF-xBT synthesized by method-II.