Prof. Yuichi Shimakawa at Institute for Chemical Research and his research team revealed anisotropic oxygen diffusion behaviors at low temperature in some iron oxides. When the brownmillerite-structure epitaxial CaFeO2.5 thin films were reduced to the infinite-layer structure CaFeO2 by low-temperature reductions with CaH2, some of the oxygen atoms are released from and others are rearranged within the perovskite-structure framework.
By evaluating the changes and the reaction time, the research team found two oxygen diffusion pathways and the related kinetics. The team also successfully prepared [CaFeO2.5]m/[SrTiO3]n brownmillerite/perovskite artificial superlattice thin films and reduced them to[CaFeO2]m/[SrTiO3]n infinite-layer/perovskite artificial superlattices. In the selective topochemical reduction, the oxygen-ion diffusion in the artificial superlattices was confined within the two-dimensional brownmillerite layers. The results obtained by the research team will be keys to develop technologies related to energy and the environment such as solid-oxide fuel cells.