Modulated Structure of the Thermoelectric Compound [Ca2CoO 3]0.62CoO2

Yuzuru Miyazaki, Mitsuko Onoda, Takeo Oku, Masae Kikuchi, Yoshinobu Ishii, Yasuhiro Ono, Yukio Morii, Tsuyoshi Kajitani

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251 Citations (Scopus)


We have determined the crystal structure of the composite crystal [Ca 2CoO3]0.62CoO2, known as Ca 3Co4O9, by a superspace group approach. Structural parameters were refined with a superspace group of Cm (0 1 - p 0) using powder X-ray and neutron diffraction data. The compound consists of two interpenetrating subsystems of a CoO2 sheet and a distorted triple-layered NaCl-type Ca2CoO3 block, being incommensurate parallel to the b-axis. The CoO2 sheet is composed of a CdI2-type triangular Co lattice with sharing an edge of the CoO6 octahedra. In the Ca2CoO3 subsystem, "<"-shaped buckled arrangement of the atoms is found, due to the ordered arrangement of the Ca and Co atoms parallel to the c-axis. Both the subsystems have common a-, c-axes and β-angle with a = 4.8339(3) Å, c = 10.8436(7) Å and β = 98.14(1)°. The b-axis lengths are refined to be b1 = 2.8238(2) Å for the [CoO2] subsystem and b2 = 4.5582(2) Å for the [Ca2CoO 3] subsystem. An undulating arrangement of the O atom sites in the CoO2 sheets is revealed but the modulation of the Co atom site is less marked. Remarkable displacive modulation of the Co and O sites in the [Ca2CoO3] subsystem has also been observed, suggesting that a regular NaCl-type coordination is very severe for the Co-O bonds in the present compound.

Original languageEnglish
Pages (from-to)491-497
Number of pages7
JournalJournal of the Physical Society of Japan
Issue number2
Publication statusPublished - 2002 Feb


  • Cobaltite
  • Composite crystal
  • Rietveld refinement
  • Superspace group
  • Thermoelectric compound


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