Redox thermodynamics and phase composition in the system SrFeO_{3 − δ} — SrMnO_{3 − δ}

Perovskite oxides are considered promising redox materials for many fields of application, such as chemical looping processes for thermochemical air separation, oxygen pumping and fuel production, in particular considering a solar heat source. The large range of possible perovskite compositions can be extended by the synthesis of solid solutions between different perovskite phases. In this work, the solid solution formation in the system SrMn_{1 − x}Fe_xO_{3 − δ} is evaluated, showing that SrFeO_{3 − δ} and SrMnO_{3 − δ} are miscible in any ratio investigated. Moreover, redox thermodynamics were studied using a van't Hoff approach. It has been found that in mixed manganese ferrite perovskites, the reduction of Fe^{4 +} is preferred over the reduction of Mn^{4 +}, leading to an increase in redox enthalpy and entropy when both species are reduced. Our findings allow the targeted synthesis of perovskites with superior redox properties for applications in chemical looping processes, as the redox thermodynamics are adjustable via variation of the Fe content.