Raman spectrum of plutonium dioxide: Vibrational and crystal field modes

Abstract

The Raman spectrum of plutonium dioxide is studied both experimentally and theoretically. Particular attention has been devoted to the identification of high-energy modes at 2120 cm -1 and 2625 cm -1 , whose attribution has so far been controversial. The temperature dependence of both modes suggests an electronic origin. Crystal Field (CF) calculations reported in this work shows that these two modes can be respectively assigned to the Γ 1 → Γ 5 and Γ 1 → Γ 3 CF transitions within the 5 I 4 manifold. These two modes, together with the only vibrational line foreseen by the group theory for the Fm-3m PuO 2 symmetrythe T 2g Pu-O stretching mode observed at 478 cm -1can thus be used as Raman fingerprint of fcc plutonium dioxide.

Laser‐induced oxidation of UO2: A Raman study

“…The estimated uncertainty was obtained by applying the method previously published by LaPlant et al . This method was shown to give satisfactory results as compared by Naji et al . for a PuO 2 sample which was externally heated in a Linkam TS1500 temperature stage.…”

“…Due to the feasibility of this laser‐induced heating, the associated temperature estimation has become an attractive target. In a recent study, Naji et al . verified that the analysis of the Stokes/anti‐Stokes intensities ratio is a reliable method for the temperature estimation in this type of experiments.…”

“…Raman spectroscopy is an analytical tool that has been established in recent years as a reliable probe for this kind of studies, as confirmed by the large increase in the specialised literature . This is due to some of its features, as that (a) it does not require any special preparation of the sample, (b) the technique allows the analysis of a very small amount of sample, (c) it requires no direct contact between the experimental set‐up and the analyte, (d) it can be easily implemented (remote analysis, Raman probes, handheld systems, etc.)…”

“…Despite the fact that this heating action of the laser has been traditionally considered an inconvenience when it comes to perform Raman measurements, as the power is usually optimised to avoid sample alteration, some authors have taken advantage of this feature for various purposes. On the one hand, detailed Raman studies have recently been performed on PuO 2 , NpO 2 , and AmO 2 , aimed primarily at the complete mode assignment of the observed Raman bands . In order to solve some discrepancies in the reported nature of peaks and their origin, a study of the evolution of their spectra as a function of laser power density has been carried out.…”

“…In order to solve some discrepancies in the reported nature of peaks and their origin, a study of the evolution of their spectra as a function of laser power density has been carried out. It has been shown that increasing the laser power density enhances the anharmonic behaviour of the T 2g mode in NpO 2 and PuO 2 , decoupling of the (Γ 8 , LO–TO ) bound state in NpO 2 and, finally, depopulation of Γ 1 → Γ 5 and Γ 1 → Γ 3 electronic crystal field excitations in PuO 2. However, no phase alteration has been detected in these materials, even at temperatures above 700 K. On the contrary, in AmO 2 , it has been observed that, even at very low power density, the laser may induce an unavoidable photolysis process when visible lasers are used, resulting in the formation of hyperstoichiometric americium sesquioxide Am 2 O 3+ z …”