Structural properties and charge distribution of the sodium uranium, neptunium and plutonium ternary oxides: a combined X-ray diffraction and XANES study


Structural properties and charge distribution of the sodium uranium, neptunium and plutonium ternary oxides: a combined X-ray diffraction and XANES study

Smith, A. L.; Martin, P.; Prieur, D.; Scheinost, A. C.; Raison, P. E.; Cheetham, A. K.; Konings, R. J. M.

The structural properties of the sodium actinide ternary oxides are reviewed in this work, and general trends among the series U-Np-Pu are identifed. A Rietveld refnement of monoclinic Na2PuO3, in space group C2~c, is reported for the first time, and the unsuspected existence of Na2NpO3 is revealed. In addition, the charge distribution in alpha-Na2UO4, Na3NpO4, alpha-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 is investigated using X-ray Absorption Near-Edge Structure (XANES) spectroscopy at the U-L3, Np-L3, and Pu-L3 edges, respectively. In contrast to measurements in solution, the number of XANES data in the literature for neptunium and plutonium solid phases with a valence state higher than (IV) is very limited. The present results cover a wide range of oxidation states, namely (IV) to (VII), and can serve as a reference databank for future investigations. Finally, the sodium actinide series show a variety of local coordination geometries, and correlations between shape of the XANES spectra and local structural environment are discussed.

Keywords: Neptunium; Plutonium; ternary oxides; XANES; XRD; Rietveld; sodium-cooled fast-neutron reactor

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Publ.-Id: 22508