Raman microspectroscopic studies of unirradiated homogeneous (U_0.76Pu_0.24)O_2+x: the effects of Pu content, non‐stoichiometry, self‐radiation damage and secondary phases

Abstract

In this study, micro-Raman spectroscopy technique was implemented to characterize an unirradiated homogeneous Gigondas (U 0.76 Pu 0.24 )O 2+x sample, which had been stored for 30 years at room temperature under air. The impacts of Pu content, deviation from stoichiometry, self-radiation damage and formation of secondary phases were assessed by comparing the Raman spectra of the aged Gigondas with an annealed sample [(U 0.76 Pu 0.24 )O 2 ]. The Pu content of the sample was measured by electron probe microanalysis technique, while the stoichiometry of the annealed Gigondas sample was determined by the results of electron probe microanalysis technique and X-ray diffraction. Two methods were proposed to explain the Raman spectrum of the aged Gigondas sample. They considered the presence of MO 2+x phase and the mixture of MO 2+x and M 4 O 9 (M: U and Pu) phases respectively. Formation of the secondary phases, which were detected on the surface of the aged Gigondas sample, could be mostly due to alpha radiolysis. It was suggested that self-radiation damage up to about 0.6 dpa leads to a shift of MO 2+x T 2g band by about 1 to 2 cm À1 towards lower wavenumbers.

Extreme multi-valence states in mixed actinide oxides

“…This mode is originated from the M-O stretching, with M being coordinated in a cubic environment of eight oxygen atoms. The presence of forbidden modes in the Raman spectra of U 1−y Am y O 2±x oxides is not surprising; it has already been observed in various UO 2 [30][31][32][33] , U-Actinide 34 and Urare earth dioxides 11,13 , as a result of breaks in the translational symmetry, which can be induced by different factors, namely irradiation, doping, reduction or oxidation.…”

Laser‐induced oxidation of UO2: A Raman study

“…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.)…”

“…On the other hand, laser heating has been employed for analysing the oxidation behaviour and/or resistance of uranium‐based materials such as (U, Pu)O 2, (U, La)O 2, and even spent fuels . In these studies, oxidation of the samples to higher oxidation‐state phases has been observed by Raman spectroscopy, using the laser as a heat source.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…Talip et al used Raman microspectroscopy to study unirradiated homogeneous (U 0.76 Pu 0.24 )O 2+x to assess the effects of Pu content, nonstoichiometry, self‐radiation damage, and secondary phases. In this study, micro‐Raman spectroscopy was used to characterize an unirradiated homogeneous Gigondas (U 0.76 Pu 0.24 )O 2+x sample, which had been stored for 30 years at room temperature under air The impacts of Pu content, deviation from stoichiometry, self‐radiation damage and formation of secondary phases were assessed by comparing the Raman spectra of the aged Gigondas with an annealed sample (U 0.76 Pu 0.24 )O 2 …”