Electronic structure of Ca3 Co4 O9 studied by photoemission spectroscopy: Phase separation and charge localization

Y. Wakisaka*, S. Hirata, T. Mizokawa, Y. Suzuki, Y. Miyazaki, T. Kajitani


研究成果: Article査読

56 被引用数 (Scopus)


We report on an electronic structure study of a quasi-two-dimensional Co oxide Ca3 Co4 O9 with Ca2 CoO3 rocksalt layers and CoO2 triangular lattice layers by means of x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), configuration-interaction calculation on a CoO6 cluster model, and unrestricted Hartree-Fock calculation on a multiband d-p model. The Co2p XPS spectrum shows that the Co valence of the rocksalt layer is similar to that of the triangular lattice layer. The cluster-model analysis of the Co2p XPS spectrum indicates that the Co sites of the rocksalt and triangular lattice layers commonly have charge-transfer energy Δ of ∼1.0 eV, d-d Coulomb interaction U of ∼6.5 eV, and transfer integral (pdσ) of ∼-2.3 eV. The Co3d t2g peak in the valence-band XPS spectrum remains sharp even above the spin-state transition temperature at ∼380 K, indicating that the spin-state transition is different from the low-spin to intermediate-spin or high-spin transitions in perovskite LaCoO3. The line shape of the UPS spectrum near the Fermi level can be reproduced by the combination of unrestricted Hartree-Fock results for the charge-ordered insulating (COI) and paramagnetic metallic (PM) states. The analysis shows that the phase separation between the COI and PM states plays important roles in Ca3 Co4 O9.

ジャーナルPhysical Review B - Condensed Matter and Materials Physics
出版ステータスPublished - 2008 12月 1

ASJC Scopus subject areas

  • 電子材料、光学材料、および磁性材料
  • 凝縮系物理学


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