Solid-state miscibility gap and thermodynamics of the system BaO–SrO

Abstract

A solid-state miscibility gap in the pseudo-binary system BaO–SrO is delineated by X-ray diffraction studies on samples equilibrated either in vacuum or under flowing inert gas at temperatures between 1073 and 1423 K. For the Sr_XBa_1–xO solid solution an asymmetric phase boundary, characterized by a critical temperature of 1356 (±4)K and composition x= 0.55 (±0.008), is obtained. Thermodynamic mixing properties of the solid solution, derived from the experimental phase boundary compositions and temperatures, can be represented by the expression: ΔG^E=x(1–x){33 390–7.09Tx+(29 340–6.237T)(1–x)} J mol^–1. It is necessary to include excess entropy terms to obtain a good fit to the experimental data. The chemical spinodal curve is computed from the thermodynamic parameters.