Oxygen driven defect and spin engineering in Ba0.5Sr0.5Co0.8Fe0.2O3–δ at high temperatures

Non-stiochiometric Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ oxide and its aluminum doped derivative were synthesized via combustion of organometallic precursors. The oxygen content was measured with temperature/oxygen partial pressure by thermogravimetry and coulometric titration techniques. A consistent defect formation model was developed for the first time. Aluminum doping was shown to reduce oxygen content and promote cobalt reduction. The model incorporates the coexistence of energetically non-equivalent oxygen sites, which were explicitly utilized in simulations. Functional dependencies of equilibrium defect concentrations, derived directly from the proposed defect structure, enable deep analysis of spin distribution over the 3d cations. Analysis of in-situ temperature dependent magnetic susceptibility measurements directly linked spin configurations of Co and Fe ions to their local environment. The validated model provides a fundamental basis for the rational design of functional cobaltite perovskites for high-temperature redox and ion transport applications and offers a tool for interpreting future transport property studies and thermal expansion behavior.