Electronic structure and large thermoelectric power in Ca 3Co4O9

T. Takeuchi, T. Kondo, K. Soda, U. Mizutani, R. Funahashi, M. Shikano, S. Tsuda, T. Yokoya, S. Shin, T. Muro

Research output: Contribution to journalArticlepeer-review

39 Citations (Scopus)


Resonant photoemission spectroscopy, soft X-ray emission spectroscopy, soft X-ray absorption spectroscopy, and high-resolution (ΔE ≈ 10 meV) ultraviolet photoemission spectroscopy were performed on a layered cobalt oxide, Ca3Co4O9, which has attracted interests as one of the potential thermoelectric materials because of its possession of high thermoelectric power S, relatively low electrical resistivity ρ, and small thermal conductivity κ. A narrow band of 1.5-2eV in width was observed in the photoemission spectra with its center at 1.0eV below the Fermi level (E F). This peak turns out to be less significant when Co 2p-3d resonance takes place, indicating that it consists mainly of O 2p and of small amount of Co 3d component. Since EF is located near the high-energy edge of this narrow band, the density of states at EF is finite but negligibly small at room temperature. An energy-gap across EF opens below 50K with decreasing temperature. This development of the energy-gap causes the insulating behavior; divergence both in electrical resistivity and Hall coefficient. We calculated thermoelectric power S(T) using the photoemission spectra near EF. The calculated S(T) shows almost half of the measured value. Large thermoelectric power up to 200 μV/K observed for the Ca3Co4O9 is closely related to the metallic electron transport in a less dispersive band with EF near its band-edge.

Original languageEnglish
Pages (from-to)595-599
Number of pages5
JournalJournal of Electron Spectroscopy and Related Phenomena
Issue numberSPEC. ISS.
Publication statusPublished - Jul 2004
Externally publishedYes


  • Cobalt oxide
  • RPES
  • Thermopower
  • UPS
  • XAS
  • XES

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Radiation
  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry


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