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Zusammenfassung:
We present soft-x-ray absorption spectra (XAS) of LaCoO3 taken at different temperatures (80-630 K). The shape of the multiplets in the Co 2p XAS spectra conveys information on the symmetry and spin of the ground state. The 0 Is XAS spectra are related to unoccupied metal bands through covalent mixing. The changes in the spectra taken at different temperatures provide information on the spin-state transition in this compound. At low temperature, 80 and 300 K, the material is in a highly covalent low-spin state. The main contribution to the ground state in this case is given by t2g6 (1A1) with an occupancy of 0.56. At higher temperature, 550 and 630 K, the results indicate a gradual transition to a mixed-spin state. The main contribution to the high-spin part of the mixture is given by t2g4e(g)2(5T2) with an occupancy of 0.71. There is no evidence of charge disproportionation in the temperature range 80-630 K. The O 1s XAS spectra reflect important changes in the unoccupied Co 3d bands across the spin-state transition.
