High-temperature transport and stability of SrFe1−xNbxO3 − δ

The conductivity is measured in the series of solid solutions SrFe1 − xNbxO3 − δ, where x = 0.05, 0.1, 0.2, 0.3, 0.4, within the oxygen partial pressure limits 10−18–0.5 atm and temperature range 650–950 °C. The contributions to the total conductivity from oxygen ions, electrons and electron holes are obtained based on their different pressure dependences. The doped derivative with x = 0.1 is found to be a singular composition where ion conductivity attains a maximal value while activation energy for ion transport is minimal. This peculiar behavior is attributed to formation of favorable microstructure in the oxide. The deeper doping results in deterioration of ion transport, which is explained by oxygen vacancy filling. It is shown that replacement of iron for niobium favors enhanced thermodynamic stability towards reduction. The oxygen permeability is evaluated from the conductivity data, and it achieves rather high values in the doped derivatives. These oxides can, therefore, be recommended for further evaluation as oxygen separating membrane materials for partial oxidation of natural gas.

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