Local structure and oxidation state of uranium in some ternary oxides: X-ray absorption analysis

We investigated the local atomic and electronic structures of two related systematic sets of ternary uranium oxid,es, NaUO3,KUO3,RbUO3 and BaUO3,,Ba2U2O7, BaUO4, by measuring the X-ray absorption near edge structure (XANES). The results are compared with calculations based on a self-consistent real space full multiple scattering analysis. We found a very good agreement between measured and calculated spectra, which indicates that the uranium ions are in a pure U5+ oxidation state in these compounds. The low energy shoulder observed in the U L3 edge XANES is an intrinsic feature of the uranium unoccupied 6d electronic states of the U5+ ions within the studied materials. Specific double shoulder features in the higher energy range of the U L3 edge XANES can be interpreted as indicative of the pure cubic perovskite structure.