The electronic structure of uranium dioxide: an oxygen K-edge x-ray absorption study

The O K-edge x-ray absorption near edge structure (XANES) spectrum of UO2 is presented and interpreted. A comparison with that corresponding to CeO2 is made. First-principles-based calculations using the LSDA+U approach allows us to link each feature present in the spectra to the specific atomic arrangement and electronic structure of the compound. The structures at the edge originate from oxygen 2p states hybridized with U 5f and 6d orbitals and the 6d eg - t2g splitting is found to be 4.8 eV. The structures due to O 2p - U 5f hybridization are found to be lower in energy than the structures due to the O 2p - U 6d hybridization. On this basis, UO2 can be considered as an f-f Mott-Hubbard insulator. (author)