Raman spectra, X-ray diffraction and infrared absorption of a series of LixCo0.9Ga0.1O2-HT oxides were obtained for 0.3 less than or equal to x less than or equal to 1.0. The Raman scattering for the lithium de-intercalated materials indicate that laser irradiation induces the formation of an impurity-phase that increases when the state of delithiation increases. The impurity-phase was identified as the Co3O4 cubic spinel structure by comparison of its Raman spectrum and those of related compounds with spectra for LixCo0.9Ga0.1O2-HT. Infrared absorption and X-ray diffraction spectra show no trace of Co3O4. This fact leads to the conclusion that Co3O4 is generated just in small areas subjected to intense light irradiation, such as the laser focus spots in micro Raman experiments. (C) 2004 Elsevier B.V. All rights reserved.