Crystal structure and electrical properties of 0.7BiFeO₃–0.3Ba_1-xSr_xTiO₃ solid solutions (x ≤ 0.3)

Solid solutions of the 0.7BiFeO₃–0.3Ba_1-xSr_xTiO₃ system with compositions in the vicinity of the rhombohedral-cubic morphotropic phase boundary (x ≤ 0.3) have been synthesized via solid state reactions. The crystal structure and morphology of the solid solutions have been studied using X-ray diffraction, scanning electron microscopy and Raman spectroscopy, and the chemical composition has been studied using energy dispersive X-ray spectroscopy. The dielectric properties of the compositions have been studied using impedance spectroscopy as a function of the concentration of strontium ions over a wide range of temperatures and frequencies. The structure of the solid solutions with x ≤ 0.3 contains coexisting rhombohedral and cubic phases, strontium ion substitution leading to higher cubic phase volume fraction. The x = 0 composition contains almost equal parts of coexisting phases, whereas the x > 0.25 solid solutions have single-phase cubic structures. The concentration-related changes in the phase structure of the solid solutions lead to a decrease in the lattice parameters of the coexisting phases and a nonmonotonic decrease in the electrical conductivity and the dielectric permeability of the compositions. The experimental data provide insight into specific changes of the structure and phase composition of the solid solutions in the vicinity of the rhombohedral-cubic morphotropic phase boundary and deliver better understanding of the relationship between the observed structural changes and the electrical properties of the compositions.