Discommensurate Structure in [(Ca0.90Sr0.10)2CoO3]0.61CoO2

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The crystal structure of partly Sr-substituted Co-121, i.e., "Ca3Co4Co9", single crystal is studied by means of the electron diffraction measurements and high-resolution transmission electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CoO2 sheet and a distorted three-layered (Ca,Sr)2CoO3 rock-salt (RS)-type block layers, which belong to a triclinic system. Both subsystems have common $a$-, $c$-axes and $\alpha$-, $\beta$-, $\gamma$-angle with $a = 4.8267(1)$ Å, $c = 10.9214(3)$ Å, $\alpha = 90.916(2)$°, $\beta = 98.291(5)$°, and $\gamma = 89.957(3)$°. On the other hand, the crystal structure is modulated parallel to the $b$-axis, along which the CoO2 sheet has $b_{1} = 2.8346(1)$ Å and the (Ca,Sr)2CoO3 RS-type block layer has $b_{2} = 4.6391(2)$ Å, respectively. On the basis of the $b_{1}/b_{2}$ ratio and analyzed chemical compositions, the structure analogue is formulated as [(Ca0.90Sr0.10)2CoO3]0.61CoO2. In electron diffraction patterns, there are many new satellite reflections, namely $010\bar{1}$, $020\bar{2}$, $0\bar{2}04$, and $0\bar{1}03$, which are not present in the end member Co-121, i.e., (Ca2CoO3)0.620CoO2. Because of the new superlattice reflections, the crystal structure of the Sr-doped compound is different from the end member. HREM images were taken with the incident electron beam parallel to the [0010] and [1000] directions. The basic crystal structure of the present system consists of 5-CoO2 and 3-RS subcells with $b=14$ Å being connected discommensuratedly parallel to the $a$- and $b$-axes. Systematic introduction of stacking faults parallel to the $a$–$b$ plane is also noticed.

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  • Journal of the Physical Society of Japan

    Journal of the Physical Society of Japan 77(6), 064604-064604-5, 2008-06-15

    一般社団法人日本物理学会

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各種コード

  • NII論文ID(NAID)
    110006781582
  • NII書誌ID(NCID)
    AA00704814
  • 本文言語コード
    EN
  • 資料種別
    ART
  • ISSN
    0031-9015
  • NDL 記事登録ID
    9534267
  • NDL 雑誌分類
    ZM35(科学技術--物理学)
  • NDL 請求記号
    Z53-A404
  • データ提供元
    CJP書誌  NDL  NII-ELS  JPS  JPS 
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