Oxygen nonstoichiometry and thermodynamic quantities in solid solution SrFe1–xSnxO3–δ

Abstract

The oxygen content (3–δ) variations in tin substituted derivatives SrFe1–xSnxO3–δ, where x = 0.05, 0.1, 0.17 and 0.25, of perovskite-like strontium ferrite, have been studied by coulometric titration measurements within oxygen partial pressure (pO2) range 10–19–10–2 atm at 800–950 °С. The obtained dependencies of (3–δ) from pO2 and temperature are used for calculations of partial molar thermodynamic functions of oxygen in the oxide structure. It is found that a satisfactory explanation of the experimental results can be attained within frameworks of the ideal solution model with ion and electron defects appearing in the result of oxidation and disproportionation of iron cations. The increase of the oxidation reaction enthalpy with tin content is consistent with the increase of the unit cell parameter, i.e., the stretch and relaxation of Fe-O chemical bonds.