AN X-RAY PHOTOELECTRON SPECTROSCOPY STUDY OF La1-xSrxCoO3 III. THE REDUCTION AND SURFACE STATE OF LaCoO3

The reduction of LaCoO3 has been studied by XPS. It is shown that the degree of reduction of cobalt is characterized by the peak intensity of shake-up satellite of Co 2p(1/2) level. The reduction of Co3+ to Co2+ in LaCoO2 is appeared at 400 degrees C. When LaCoO3 is reduced by H-2 at 600 degrees C, the cobalt is converted into metallic form, meanwhile the structure of La2O2 is identified by X-ray diffraction. After reduction of LaCoO3 the separation energy between La 3d(5/2) level and its shake-up satellite peak is 3.1 eV and the intensity ratio of shake-up satellite to its parent peak for La 3d(5/2) level is 0.76. These values are approximately same as those of La(OH)(3), but they are different from those La2O2. Therefore, La(OH)(2) is formed on surface after reduction of LaCoO3.