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Article Dans Une Revue Journal of Nuclear Materials Année : 2017

Identification of NpO 2+x in the binary Np-O system

Résumé

In contrast to UO2 and PuO2, there is no consensus on the existence of mixed valence NpO2+x, resulting in a gap between NpO2 and Np2O5 (the highest binary oxide of Np) in the Np-O phase diagram. We now show NpO2+x via Np LIII Extended X-ray Absorption Fine Structure (EXAFS) spectra of three samples of NpO2 that, analogous to U and Pu, exhibit multisite Np-O distributions with varying numbers of oxygen atoms at 1.87–1.91 Å. This is supported by the diffraction pattern of the sample with the largest amount of this oxo-type species that can be refined with both the simple fluorite structure and a trigonal one related to α-U4O9. The implied Np(V)-bridging oxo moieties as well as possible indications of OH¯ found by detailed EXAFS analysis suggest that NpO2+x more closely resembles PuO2+x than UO2+x. An additional common characteristic suggested by the EXAFS and X-Ray Diffraction (XRD) is the phase separation into NpO2 and what would be previously unreported Np4O9(–δ), indicative of O clustering.

Dates et versions

hal-01781612 , version 1 (30-04-2018)

Identifiants

Citer

Akhil Tayal, Steven D. Conradson, Gianguido Baldinozzi, Sonu Namdeo, Kevin Roberts, et al.. Identification of NpO 2+x in the binary Np-O system. Journal of Nuclear Materials, 2017, 490, pp.279 - 287. ⟨10.1016/j.jnucmat.2017.04.019⟩. ⟨hal-01781612⟩
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