Reduction and Oxidation of Transition-Metal Oxide Thin Films: Solid-State Chemistry with Epitaxially Grown Thin Films

Abstract

Reduction and oxidation of perovskite-structure transition-metal oxide thin films are highlighted. Oxygen ions are released from and incorporated into the perovskite-structure framework during the reduction and oxidation. Lowtemperature topochemical reduction reaction with CaH 2 enables us to prepare infinite-layer structure oxide thin films containing Fe and Ni. With the epitaxially grown thin film samples, anisotropic rearrangement and transfer of oxygen ions in the structures have been revealed. Selective reduction of layers in artificial superlattices was also found, and the observed behavior suggests that the oxygen-ion mobility in the artificial superlattices was confined within the twodimensional brownmillerite layer. Specific structural features play important roles in the oxygen-ion transfer in solids at low temperatures. The obtained results would be a key to develop technologies related to energy and the environment.

Development of a Simultaneous SANS/FTIR Measuring System

“…We expect that the present method would be able to analyze the structure and properties of functional thin films, which have become an important research field due to advances in fabrication technology. 19,20 Although we have employed this prototype system to follow the slow structural changes caused by heating in this study, we believe that this methodology can be applied to time-resolved measurement of second order by improving the FTIR system through redesigning the optical system to gain a high optical throughput and by employing a highly sensitive IR detector, such as MCT detectors. In addition to the simple transmission method that we employed to measure the IR spectra in this study, this system can be combined with other IR measurement techniques like attenuated total reflection (ATR) and reflection absorption spectroscopy (RAS) by modifying the optical system.…”

Oxygen Release and Incorporation Behaviors in BaFeO3 Polymorphs with Unusually High-Valence Fe4+

“…Among so many materials, Fe-containing perovskites are especially interesting. Fully oxygenated A FeO 3 ( A = Ca and Sr) changes to brownmillerite structure A FeO 2.5 by releasing oxygen. − Furthermore, A FeO 2.5 changes to the infinite-layer structure A FeO 2 when strong reductants such as CaH 2 are used. − These changes occur as a result of releasing oxygen topotactically in the perovskite structure framework and accompany the changes in the Fe-oxidation states. Octahedrally oxygen-coordinated Fe 4+ in A FeO 3 changes to octahedrally and tetrahedrally oxygen-coordinated Fe 3+ in A FeO 2.5 and to square-planar oxygen-coordinated Fe 2+ in A FeO 2 .…”

Structural, magnetic and electronic properties of pulsed-laser-deposition grown SrFeO3−δthin films and SrFeO3−δ/La2/3Ca1/3MnO3multilayers

“…There are only few publications that discuss the growth and the physical properties of stoichiometric as well as oxygendeficient SFO thin films [11][12][13][14][15][16][17]. In the following we therefore present first a detailed description of the growth and the characterization of the bare SFO thin films in the as-grown and the ozone annealed states, before we proceed to the corresponding SFO/LCMO multilayers.…”