We present a study of the electronic structure of oxygen-deficient ferrites SrFeO x (x = 2.46, 2.52, 2.68, and 2.82) by means of X-ray photoelectron, X-ray emission, and X-ray absorption spectroscopies. From the Fe 3s photoelectron splitting, the magnetic moments are estimated. It is found that the doped holes are localized in both Fe 3d and O 2p states. The valence band structure is analyzed. It is shown that the band gap decreases with the increase of oxygen concentration.

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The substitution of scandium for iron in the Ruddlesden−Popper Sr3Fe2 - x Sc x O7 - δ (x = 0−0.3) system increases tetragonal unit-cell volume and oxygen nonstoichiometry and decreases partial p- and n-type electronic conductivities studied in the oxygen partial pressure range from 1 × 10-20 to 0.7 atm at 973−1223 K. The solubility of Sc3+ corresponds to approximately x ≈ 0.35. The relatively low, temperature-activated hole mobility indicates a small-polaron mechanism of the electronic transport, as for undoped Sr3Fe2O7 - δ. The atomistic computer simulations showed that major contribution to the ionic conductivity is provided by the oxygen sites surrounded by iron cations in the perovskite-type layers of Sr3(Fe,Sc)2O7- δ structure, whereas stable ScO6 octahedra are essentially excluded from the oxygen diffusion processes. Minimum migration energy, 0.9−1.4 eV, was found for nonlinear pathways formed by the apical O1 sites linking iron−oxygen polyhedra along the c-axis and equatorial O3 positions in the perovskite-type planes. The direct O3 → O3 jumps are characterized with higher energetic barrier, 1.5−2.2 eV. Because of the increasing concentration of vacant O3 sites induced by scandium doping, the apparent activation energy for oxygen−ionic transport decreases from about 2 eV, as observed for undoped strontium ferrite at 1123−1223 K, down to 0.95−1.15 eV for Sr3Fe2 - x Sc x O7 - δ (x = 0.2−0.3). As a result, the partial ionic conductivity of Sr3Fe1.7Sc0.3O7- δ at temperatures below 1000 K becomes higher than that in Sr3Fe2O7 - δ.