Uranium oxides investigated by X-ray absorption and emission spectroscopies

TL;DR

This study uses X-ray absorption and emission spectroscopies to analyze the electronic structure and hybridization differences in various uranium oxides, revealing site-specific spectral behaviors and energy dependence.

Contribution

It provides detailed spectroscopic characterization of uranium oxides and links spectral features to structural and electronic differences, especially in UO3.

Findings

UO3 shows excitation energy-dependent spectral shapes due to site-specific hybridization.

UO2 and U3O8 exhibit different spectral shapes without significant energy dependence.

Experimental spectra align with electronic structure calculations from literature.

Abstract

X-ray absorption and resonant X-ray emission measurements at the O 1s edge of the uranium oxides UO2, U3O8 and UO3 are presented. The spectral shapes of the O K{\alpha} X-ray emission spectra of UO3 exhibit significant excitation energy dependence, from an asymmetric to a symmetric form, which differs from those of UO2 and U3O8. This energy dependence is attributed to a significant difference in the oxygen-uranium hybridization between two different sites in the crystal structure of UO3. The spectral shapes of UO2 and U3O8 are also found to be different but without significant energy dependence. The experimental spectra of the valence and conduction bands of the uranium oxides are compared to the results of electronic structure calculations available in the literature.