Oxygen Permeable Properties of Ce 0.8 Gd 0.2 O 1.9 - MFe 2 O 4 Composite Thin Films Prepared by a Chemical Solution Depo
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Oxygen Permeable Properties of Ce0.8Gd0.2O1.9 - MFe2O4 Composite Thin Films Prepared by a Chemical Solution Deposition Method Isao Kagomiya1, 2, Takashi Iijima1 and Hitoshi Takamura3 1 Research Institute Instrumental Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1, Umezono, Tsukuba 305-8568, Japan 2 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 2-1-13, Higashi-Ueno, Taito-ku, Tokyo 110-0015, Japan 3 Department of Materials Science, Graduate School of Engineering, Tohoku University, Aoba 6-6-02, Sendai 980-8579, Japan ABSTRACT Ce0.8Gd0.2O1.9 (CGO) - MFe2O4 (M=divalent cation) is a composite-type oxygen-ionic and electronic mixed conductor. Dense nanocrysalline CGO-CoFe2O4 thin films with a thickness of approximately 1 µm were prepared on CGO porous substrates by a chemical solution spin-coating method. The oxygen permeable flux of the thin film was investigated in temperature range of 700°C - 800°C without physical leak of N2 gas. The permeable flux depends on the measuring time, when the measuring temperature was kept at 750°C before increasing to 800°C. This fact suggests that the O2 permeable properties were affected by a slight change of the film morphology and the crystallinity. INTRODUCTION The development of oxides with enhanced electric and oxygen-ionic conductivity (mixed conductivity) is of importance for devices based on electrochemical reactions such as gas sensors, fuel cell electrodes and oxygen separating membrane. In particular, we are highly interested in the production of syngas (H2 + CO) using the mixed conductive oxides.[1] Membranes combining high oxygen permeability with phase stability under the high oxygen partial pressure deference are required to perform a feasible application for the syngas production. We suppose that Ce0.8Gd0.2O1.9 (CGO) - spinel-type ferrite MFe2O4 (M=divalent cation), which is a composite-type mixed conductor, is a possible candidate.[2] In this system, the spinel ferrite MFe2O4 strongly supports an electronic conductivity, while the CGO takes a main part of ionic conduction. The oxygen permeable flux density of the system is as high as that of mixed conductive perovskite-type such as La-Sr-Co-Fe oxides. [3,4] In addition, this composite system has good stability under both reduction- and oxidation- atmospheres. Previously, we have prepared CGO-CoFe2O4 thin films on porous CGO substrates using a chemical solution deposition spin-coating method and investigate the oxygen permeable flux at 1000°C. The oxygen permeable flux density exceeds that obtainable using a bulk material. [5] The chemical solution deposition technique is advantageous to preparation of dense nanocrystalline thin films, resulting that the sintering temperature for the preparation can be reduced down to below 1000°C, which is much lower than that of conventional powder reaction method. Some electric conductive studies have reported that the nanocrystalline mixed conductive oxides
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