Modulated Structure of Misfit-Layered Cobalt Oxide [Ca2(Co 0.65Cu0.35)2O4] 0.63CoO2

Yuzuru Miyazaki, Tatsuro Miura, Mitsuko Onoda, Masaya Uchida, Yoshinobu Ishii, Yasuhiro Ono, Yukio Morii, Tsuyoshi Kajitani

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Abstract

We have determined the crystal structure of novel thermoelectric compound [Ca2(Co0.65Cu0.35)2O 4]0.63CoO2 by a superspace group approach. Structural parameters have been refined with a superspace group of C2/m(1 p 0) s0 using powder neutron diffraction data collected at 293 K. The compound consists of mutually interpenetrating triangular CoO2 layers and distorted four-layered rock salt-type Ca2(Co0.65Cu 0.35)2O4 slabs, which are incommensurate parallel to the b-axis. The CoO2 layer is composed of the CdI 2-type edge-shared CoO6 octahedra. Both the subsystems have common a- and c-axes, and β-angle with a = 4.8212(4) Å, c = 12.7671(8) Å and β= 93.93(1)°. The e-axis lengths are b 1 = 2.8103(3) Å for the [CoO2] subsystem and b 2 = 4.4915(3) Å for the [Ca2(Co 0.65Cu0.35)2O4] subsystem. A marked displacive modulation of the (Co,Cu) and O sites in the [Ca2(Co 0.65Cu0.35)2O4] subsystem has been observed, yielding a large fluctuation of the (Co,Cu)-O distances in the range from 1.8 Å to 2.7 Å. Cu2+ ions appear to play an important role in stabilizing such a four-atom thick subsystem in this compound.

Original languageEnglish
Pages (from-to)7467-7473
Number of pages7
JournalJapanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
Volume42
Issue number12
Publication statusPublished - 2003 Dec 1

Keywords

  • Calcium cobalt copper oxide
  • Misfit-layered structure
  • Rietveld refinement
  • Superspace group
  • Thermoelectric compound

ASJC Scopus subject areas

  • Engineering(all)
  • Physics and Astronomy(all)

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