Improving understanding of NpO2 and Np2O5 through vibrational spectroscopy

Raman spectra of three NpO₂ samples and two samples produced from a modified direct denitration (MDD) process were collected. The spectral features of the NpO₂ samples were consistent and indicated only NpO₂. The spectra of the MDD samples indicated the presence of NpO₂ and an additional phase attributed to the neptunium binary oxide Np₂O₅. These Raman spectra are the first reported of Np₂O₅, and the proportions of these neptunium oxide phases varied within the samples, suggesting significant sample inhomogeneity. Peaks in the Raman spectra of Np₂O₅ at 569 and 782 cm⁻¹ were tentatively assigned to concerted, symmetric stretches of the neptunyl cations. Laser-induced heating of regions in the MDD samples that were rich in Np₂O₅ showed spectral features that indicated conversion to NpO₂.