Refinement of the uranium dispersion corrections from anomalous diffraction

Gregory Leinders, Ola Gjonnes Grendal, Ine Arts, René Bes, Igor Prozheev, Simon Orlat, Andrew Fitch, Kristina Kvashnina, Marc Verwerft

    Research outputpeer-review


    The evolution of the uranium chemical state in uranium compounds, principally in the oxides, is of concern in the context of nuclear fuel degradation under storage and repository conditions, and in accident scenarios. The U–O system shows complicated phase relations between single-valence uranium dioxide (UO2) and different mixed-valence compounds (e.g. U4O9, U3O7 and U3O8). To try resolving the electronic structure associated with unique atomic positions, a combined application of diffraction and spectroscopic techniques, such as diffraction anomalous fine structure (DAFS), can be considered. Reported here is the application of two newly developed routines for assessing a DAFS data set, with the aim of refining the uranium X-ray dispersion corrections. High-resolution anomalous diffraction data were acquired from polycrystalline powder samples of UO2 (containing tetravalent uranium) and potassium uranate (KUO3, containing pentavalent uranium) using synchrotron radiation in the vicinity of the U L3 edge (17.17 keV). Both routines are based on an iterative refinement of the dispersion corrections, but they differ in either using the intensity of a selection of reflections or doing a full-pattern (Rietveld method) refinement. The uranium dispersion corrections obtained using either method are in excellent agreement with each other, and they show in great detail the chemical shifts and differences in fine structure expected for tetravalent and pentavalent uranium. This approach may open new possibilities for the assessment of other, more complicated, materials such as mixed-valence compounds. Additionally, the DAFS methodology can offer a significant resource optimization because each data set contains both structural (diffraction) and chemical (spectroscopy) information, which can avoid the requirement to use multiple experimental stations at synchrotron sources.

    Original languageEnglish
    Pages (from-to)284-295
    Number of pages12
    JournalJournal of Applied Crystallography
    Issue numberPt 2
    StatePublished - Apr 2024

    ASJC Scopus subject areas

    • General Biochemistry,Genetics and Molecular Biology

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