Impact of oxygen content on preferred localization of p- and n-type carriers in La0.5Sr0.5Fe1-xMnxO3-delta

The oxygen content in La0.5Sr0.5Fe1-xMnxO3-delta, measured by coulometric titration in a wide range of oxygen partial pressure at various temperatures, was used for defect chemistry analysis. The obtained data were well approximated by a model assuming defect formation in La0.5Sr0.5Fe1-xMnxO3-delta via Fe3+ and Mn3+ oxidation reactions and charge disproportionation on Fe3+ and Mn3+ ions. The partial molar enthalpy and entropy of oxygen in La0.5Sr0.5Fe1-xMnxO3-delta obtained by statistical thermodynamic calculations were found to be in satisfactory agreement with those obtained using the Gibbs-Helmholtz equations, thus further confirming the adequacy of the model. The impact of manganese substitution on defect equilibrium in La0.5Sr0.5Fe1-xMnxO3-delta was shown to be attributed to a lower enthalpy of Mn3+ oxidation reaction (Delta H degrees(oxMn) = -256.12 kJ mol(-1) vs. Delta H degrees(oxFe) = -111.4 + 0.3 kJ mol(-1) for the oxidation of Fe3+) and the charge disproportionation reaction on Mn3+ (Delta H degrees(dMn) = 58.4 kJ mol(-1) vs. Delta H degrees(dFe) = 115.8 + 0.7 kJ mol(-1) for that on Fe3+). The former makes Mn4+ ions more resistant to reduction than Fe4+. The latter favors the presence of Mn2+, Mn3+, and Mn4+ ions in oxides in comparable concentrations. The distribution of charge carriers over iron and manganese ions was determined as a function of oxygen content in La0.5Sr0.5Fe1-xMnxO3-delta.