Thermodynamic quantities and defect formation in solid solution La0.49Sr0.5−xBaxFeO3−δ

Abstract

The key factors determining the applicability of mixed-conducting oxides in energy-related technologies refer to the stability to reduction and the level of oxygen ionic and electronic transport, both determined by partial molar enthalpy and entropy of oxygen in the oxide. Therefore, any information about the thermodynamic properties of the oxide has an important predictive value.The chemical potential of oxygen in La0.49Sr0.5−xBaxFeO3−δ relative to the standard state in the gas phase, ΔμO, was calculated using experimental data on oxygen content in oxides depending on the partial pressure of oxygen, pO2, and temperature. The partial molar enthalpy, ΔH¯O, and partial molar entropy, ΔS¯O, of oxygen were determined as functions of (3−δ) from ΔμO data using the Gibbs-Helmholtz equation. The previously proposed defect equilibrium model assuming the presence of unavailable oxygen vacancies in barium-containing oxides was successfully verified. Thermodynamic quantities ΔH¯O and ΔS¯O, obtained by statistical thermodynamic calculation based on this model were found to be in a reasonable agreement with those obtained with the Gibbs-Helmholtz equation. The performed calculations allowed enhancing the accuracy of the defect equilibrium model parameters.