Oxygen vacancy formation and the ion migration mechanism in layered perovskite (Sr,La)3Fe2O7−δElectronic supplementary information (ESI) available. See DOI: 10.1039/c4cp00736k

Metal oxides are widely used in devices such as sensors, fuel cells, and oxygen permeation membranes. Understanding the oxide ion migration mechanism would provide fundamental insights into the relationships between the structure and properties such as ionic conductivity. The Ruddlesden-Popper perovskite (Sr,La) n +1 (Fe,Co) n O 3 n +1 ( n = 2) has characteristic oxygen permeation and ion conduction properties, resulting from the layered perovskite structure. To elucidate the ion migration mechanism in Sr 2.46 La 0.54 Fe 2 O 7− δ (SLF) we used a combination of experimental techniques [X-ray powder diffraction (XRPD) and enthalpy investigations of the oxygen vacancy formation reaction] and computational techniques [the bond valence sum (BVS) approach and ab initio density functional theory (DFT)]. The structural analyses of SLF by XRPD and DFT agreed well. They showed that the oxygen vacancies in SLF are located at the O1 oxygen site, which is on the vertex shared by two FeO 6 octahedra in the perovskite layer. Enthalpy of the oxygen vacancy formation changed at 830 °C. This is similar to the ionic conduction behavior reported for Sr 3 Fe 2 O 7 . The XRPD study indicates that the host structural framework did not change with temperature, while the oxygen/vacancy arrangement in SLF did change at 830 °C. The BVS and DFT studies suggested a change in the ion migration pathway, in which the ion migration through O1 sites becomes more important at temperatures higher than 830 °C. The characteristic ion migration mechanism for Sr 2.46 La 0.54 Fe 2 O 7− δ was investigated by combination of experiments [X-ray diffraction, enthalpy investigations of vacancy formation] and computations [bond valence sum, ab initio density functional theory].