We report on an electronic structural study of LixCoO 2 single crystals (x=0.99, 0.71, 0.66, and 0.46) which have hole-doped CoO2 triangular lattices. The valence-band photoemission spectra show that the Fermi level is located near the top of the Co3d t 2g bands and that, by the reduction in x, the Co3d t2g peak is shifted to the lower binding-energy side. This energy shift is consistent with the chemical-potential shift by the hole doping to the t 2g bands. The fine structures near the Fermi level indicate the splitting of the t2g bands into the a1g and e g′ components. The electronic structure parameters such as the charge-transfer energy Δ are obtained by the cluster-model analysis of the Co2p core-level spectra. The unrestricted Hartree-Fock calculation using the obtained parameter values predicts that the doped holes are accommodated by the a1g band up to the doping level x of 0.46 which is consistent with the observation in the valence-band spectra. However, the valence-band spectra cannot be reproduced by the unrestricted Hartree-Fock calculation indicating that the correlation effect from the electron-electron and electron-phonon interactions is substantial in LixCoO 2.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 2010 8月 13
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