Structural order and disorder in Co-based layered cuprates CoSr2(Y,Ce)sCu2O5+2s (s=1-3) |
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Authors: | T. Nagai V.P.S. Awana A. Yamazaki H. Yamauchi W.B. Yelon |
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Affiliation: | a National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japanb Department of Resources and Environmental Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku, Tokyo 169-8555, Japanc Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japand Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, Indiae Graduate Center for Materials Research, University of Missouri-Rolla, MO 65409, USA |
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Abstract: | Crystal structures of a homologous series of Co-based layered cuprates, CoSr2(Y,Ce)sCu2O5+2s (s=1-3), have been investigated by high-resolution electron microscopy (HREM) and electron diffraction (ED) techniques. For all the three phases ED patterns showed double periodicity along a direction parallel to the CoO layers, indicating a regular alternation of two types of CoO4-tetrahedra chains within the layers. Also seen was ordering of the chains along the layer-stacking direction for the s=1 phase (Co-1212); ED patterns simulated based on the proposed superstructure model well reproduced the observed patterns. For the s=2 (Co-1222) and s=3 (Co-1232) phases in which an additional fluorite-type layer-block is inserted between two CuO2 planes, HREM and ED analysis revealed complete disorder of the CoO4 chains along the layer-stacking direction. This implies that the interlayer ordering is mainly controlled by the distance between the neighboring CoO layers. |
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Keywords: | Co-based cuprates Fluorite-type block Superstructure Electron diffraction High-resolution electron microscopy |
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