title: Strain-induced significant increase in metal-insulator transition temperature in oxygen-deficient Fe oxide epitaxial thin films.
abstract: Oxygen coordination of transition metals is a key for functional properties of transition-metal oxides, because hybridization of transition-metal d and oxygen p orbitals determines correlations between charges, spins and lattices. Strain often modifies the oxygen coordination environment and affects such correlations in the oxides, resulting in the emergence of unusual properties and, in some cases, fascinating behaviors. While these strain effects have been studied in many of the fully-oxygenated oxides, such as ABO3 perovskites, those in oxygen-deficient oxides consisting of various oxygen coordination environments like tetrahedra and pyramids as well as octahedra remain unexplored. Here we report on the discovery of a strain-induced significant increase, by 550 K, in the metal-insulator transition temperature of an oxygen-deficient Fe oxide epitaxial thin film. The observed transition at 620 K is ascribed to charge disproportionation of Fe(3.66+) into Fe(4+) and Fe(3+), associated with oxygen-vacancy ordering. The significant increase in the metal-insulator transition temperature, from 70 K in the bulk material, demonstrates that epitaxial growth of oxygen-deficient oxides under substrate-induced strain is a promising route for exploring novel functionality.
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Hirai
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kan
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Noriya
authors.initials: N
authors.lastname: Ichikawa
authors.affiliation: Nagoya Institute of Technology, Nagoya, Aichi 466-8555, Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Mibu
authors.affiliation: Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Yoda
authors.affiliation: Faculty of Physics, M. V. Lomonosov Moscow State University, 119991, Moscow, Russia.
authors.forename: Marina
authors.initials: M
authors.lastname: Andreeva
authors.affiliation: 1] Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan [2] Japan Science and Technology Agency, CREST, Uji, Kyoto 611-0011, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Shimakawa