Preparation and Oxygen Permeability of La-Sr-Co-Fe Oxide Thin Films by a Chemical Solution Deposition Process
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Preparation and Oxygen Permeability of La-Sr-Co-Fe Oxide Thin Films by a Chemical Solution Deposition Process Hirofumi Kakuta1, 2, Takashi Iijima1 and Hitoshi Takamura3 1 Smart Structure Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 2, 1-1-1, Umezono, Tsukuba 305-8568, Japan 2 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), 2-1-13, Higashi-Ueno, Taito-ku, Tokyo 110-0015, Japan 3 Department of Materials Science, Graduate School of Engineering, Tohoku University Aoba-yama02, Sendai 980-8579, Japan ABSTRACT Oxygen-ionic and electronic conductive thin films with the composition of La0.6Sr0.4Co0.5Fe0.5O3-α (LSCF) were prepared on a porous alumina substrate by a chemical solution deposition (CSD) process and their oxygen permeating flux densities were measured. Thickness of the LSCF layer on the substrate was about 0.4 µm. Oxygen flux density of the LSCF sample was found to be 0.6 µmol·cm-2·s-, however, time-dependent degradation of oxygen flux was observed. The CeO2 barrier layer between the LSCF layer and the substrate was effective in order to improve time-dependent degradation of oxygen flux.
INTRODUCTION Oxygen-ionic and electronic mixed conductors have been receiving much attention for the usage in a variety application such as gas sensors and fuel cell electrodes. Moreover, it can be applied to an oxygen permeating membrane [1-4]; oxygen gas can selectively pass through the membrane made of the mixed conductor from high oxygen pressure side to low oxygen pressure side at elevated temperatures. This material is expected to manufacture pure oxygen at a lower cost, however oxygen-permeating flux of bulk materials is insufficient so far. It is required to increase the oxygen flux density of mixed conductors. One of the approaches to increase oxygen flux is to decrease the thickness of mixed conductive ceramics, because oxygen-permeating flux is in inverse proportion to the thickness of the membrane within certain limitation [3]. The bulk sample was generally cut and polished to prepare the membrane, but this method has a limitation of decreasing the thickness, since the mechanical strength decreases with decreasing the thickness. The oxygen permeating membrane should be supported by a porous substrate to permeate the gases if the membrane thickness is less than about 150 µm. It is required to prepare thinner films than 150 µm. The mixed conductive thin films have been prepared on the porous support [5-7]. However, oxygenpermeating flux was not successfully measured because it is difficult to obtain dense films. Chemical solution deposition (CSD) process is one of the promising techniques to prepare ceramic films on dense substrates in a variety filed including superconductors [8] and ferroelectric materials [9]. This study utilized the CSD process coupled with a spin coating technique in order to obtain dense mixed conductive films. As a mixed conductor, we made choice of the La-Sr-Co-Fe system
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