Crystal structure of the parent misfit-layered cobalt oxide [Sr2O2]qCoO2 |
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Authors: | T. Nagai K. Sakai T. Asaka A. Yamazaki Y. Matsui |
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Affiliation: | a High Voltage Electron Microscopy Station, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan b Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan c Department of Resources and Environmental Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku, Tokyo 169-8555, Japan |
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Abstract: | The crystal structure of our newly discovered Sr-Co-O phase is investigated in detail through high-resolution electron microscopy (HREM) techniques. Electron diffraction (ED) measurement together with energy dispersive X-ray spectroscopy (EDS) analysis show that an ampoule-synthesized sample contains an unknown Sr-Co-O ternary phase with monoclinic symmetry and the cation ratio of Sr/Co=1. From HREM images a layered structure with a regular stacking of a CdI2-type CoO2 sheet and a rock-salt-type Sr2O2 double-layered block is observed, which confirms that the phase is the parent of the more complex “misfit-layered (ML)” cobalt oxides of [MmA2Om+2]qCoO2 with the formula of [Sr2O2]qCoO2, i.e. m=0. It is revealed that the misfit parameter q is 0.5, i.e. the two sublattices of the CoO2 sheet and the Sr2O2 block coexist to form a commensurate composite structure. We propose a structural model with monoclinic P21/m symmetry, which is supported by simulations of ED patterns and HREM images based on dynamical diffraction theory. |
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Keywords: | Misfit-layered cobalt oxide Strontium cobalt oxide Thermoelectric material Transmission electron microscopy Electron diffraction High resolution electron microscopy |
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