Identification of NpO2+x in the binary Np-O system

A reanalysis of the EXAFS of NpO2 finds a multisite Np-O distribution with Np(V)-oxo moieties at 1.88-1.91 Å. The structure and behavior of NpO2+x more closely resemble PuO2+x than UO2+x.In addition EXAFS and XRD results indicate phase separation into NpO2 and previously unreported Np4O9(-δ), signifying O clustering.143