Author: ["Satoru Inoue","Masanori Kawai","Noriya Ichikawa","Hiroshi Kageyama","Werner Paulus","Yuichi Shimakawa"]
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Abstract
Oxygen-ion conduction in transition-metal oxides is exploited in, for example, electrolytes in solid-oxide fuel cells and oxygen-separation membranes, which currently work at high temperatures. Conduction at low temperature is a key to developing further utilization, and an understanding of the structures that enable conduction is also important to gain insight into oxygen-diffusion pathways. Here we report the structural changes observed when single-crystalline, epitaxial CaFeO2.5 thin films were changed into CaFeO2 by low-temperature reductions with CaH2. During the reduction process from the brownmillerite CaFeO2.5 into the infinite-layer structure of CaFeO2, some of the oxygen atoms are released from and others are rearranged within the perovskite-structure framework. We evaluated these changes and the reaction time they required, and found two oxygen diffusion pathways and the related kinetics at low temperature. The results demonstrate that oxygen diffusion in the brownmillerite is highly anisotropic, significantly higher along the lateral direction of the tetrahedral and octahedral layers. The movement of oxygen ions through materials is important in electrolytes and separation membranes, but is rare at lower temperatures. Two different low-temperature diffusion pathways are revealed during the reduction process of CaFeO2.5 to CaFeO2. The two pathways are significantly different, resulting in anisotropy. Cite this article
Inoue, S., Kawai, M., Ichikawa, N. et al. Anisotropic oxygen diffusion at low temperature in perovskite-structure iron oxides. Nature Chem 2, 213–217 (2010). https://doi.org/10.1038/nchem.547 