Electronic structure of defective lithium cobaltites Li x CoO2

Abstract

X-ray absorption, resonant X-ray emission, and X-ray photoelectron spectroscopical methods have been applied for the study of the electronic structure of defective lithium cobaltites LixCoO2 (0.6≤x≤1.0). Resonant O Kα X-ray emission spectra of LiCoO2 showed localized excitonic states due to a dd transition between occupied and unoccupied Co 3d states. On the base of measurements of Co 3s X-ray photoelectron, Co 2p, and O 1s X-ray absorption spectra, it was established that in defective cobaltites the electronic holes are localized mainly in O 2p states. An evidence of phase separation in LixCoO2 has been found. It was shown that the semiconductor-to-metal transition in LixCoO2 (x<0.76) at about 160 K is not accompanied by changes in the Co 3d electronic configuration which remains 3d6.