Crystal structure and thermoelectric properties of the misfit-layered cobalt oxides

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Abstract

On the basis of the crystal chemistry and electronic structure of γ-NaxCoO2, we explored many cobalt-based oxide systems and encountered the compound "Ca3Co4O 9". Through the detailed structure analyses, the cobalt oxide has been revealed to be a misfit-layered compound, which consists of two interpenetrating monoclinic subsystems. The first subsystem [CoO2] has a CdI2-type triangular lattice while the second subsystem [Ca2CoO3] is built up from an ordered three-layered NaCl-type (RS) block. The structure formula can be expressed as [Ca 2CoO3]pCoO2, where p stands for the b-axis ratio, bCoO2/bRS ∼ 0.62. A typical polycrystalline sample of the compound exhibits reasonable thermoelectric (TE) performance with thermopower S = 130 μV K-1, resistivity = 15 mΩ cm and thermal conductivity κ = 1 W m-1 K -1 at 300 K. The resulting figure-of-merit Z (S 2/ρκ) = 1.1 × 10-4 K-1 is comparable to that of polycrystalline samples of the γ-phase, indicating that the present misfit cobalt oxide is a potential candidate for a thermoelectric material.

Original languageEnglish
Pages (from-to)463-467
Number of pages5
JournalSolid State Ionics
Volume172
Issue number1-4 SPEC. ISS.
DOIs
Publication statusPublished - 2004 Aug 31

Keywords

  • Crystal structure
  • Misfit-layered compounds
  • Modulated structure
  • Superspace group
  • Thermoelectrics

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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