High-temperature thermodynamic and transport properties of the [formula omitted] mixed conductor

Abstract

We report a systematic study of the non-stoichiometry and high-temperature transport properties of the perovskite related mixed conductor Sr 3 Fe 2 O 6 + δ . The variation of the oxygen content ( 6 + δ ) with T and equilibrium oxygen partial pressure ( p O 2 ) was obtained by thermogravimetry within the range: 10 - 5 < p O 2 < 1 atm . ; 400 ⩽ T ⩽ 1100 ∘ C . From the experimental values of the oxygen chemical potential ( μ O 2 ), the partial molar enthalpy ( h O 2 ) and the partial molar entropy ( s O 2 ) were determined for the composition range 6.00 < 6 + δ < 6.55 . A simple defect model based on the mass action law assuming localized charge carriers and oxygen vacancies was used to reproduce the thermodynamic data. Electrical resistivity measurements as a function of p O 2 at constant temperature were obtained within the interval 650 ⩽ T ⩽ 1000 ∘ C . The activation energy values for the electrical transport process at constant oxygen content values were obtained from the combination of electrical conductivity and thermogravimetry data. The electrical transport data are in agreement with the small polaron model.