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Local Structure in U(IV) and U(V) Environments: The Case of U3O7

Leinders, G.; Bes, R.; Kvashnina, K.; Verwerft, M.
A comprehensive analysis of X-ray absorption data obtained at theUL3-edge for a systematic series of single-valence (UO2, KUO3,UO3) and mixed-valence uranium compounds (U4O9,U3O7,U3O8) is reported. High-energyresolutionfluorescence detection (HERFD) X-ray absorption near-edge spectros-copy (XANES) and extended X-ray absorptionfine structure (EXAFS) methodswere applied to evaluate U(IV) and U(V) environments, and in particular, toinvestigate the U3O7local structure. Wefind that the valence state distribution inmixed-valence uranium compounds cannot be confidently quantified from aprincipal component analysis of the UL3-edge XANES data. The spectral linebroadening, even when applying the HERFD-XANES method, is sensibly higher(∼3.9 eV) than the observed chemical shifts (∼2.4 eV). Additionally, the white line shape and position are affected not only by thechemical state, but also by crystalfield effects, which appear well-resolved in KUO3. The EXAFS of a phase-pure U3O7sample wasassessed based on an average representation of the expanded U60O140structure. Interatomic U−O distances are found mainly tooccur at 2.18 (2), 2.33 (1), and 3.33 (5) Å, and can be seen to correspond to the spatial arrangement of cuboctahedral oxygenclusters. The interatomic distances derived from the EXAFS investigation support a mixed U(IV)−U(V) valence character in U3O7


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Publ.-Id: 30852