Probing chemical bonding in uranium dioxide by means of high-resolution x-ray absorption spectroscopy

A systematic x-ray absorption study at the U 3d, 4d and 4f edges of UO2 was performed and the data were analyzed within framework of the Anderson impurity model. By applying the highenergy-resolution uorescence-detection (HERFD) mode of x-ray absorption spectroscopy (XAS) at the U 3d3/2 edge and by doing the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved due to reduced core-hole lifetime broadening. These allowed for more efficient analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree of the 5f localization in UO2. The results support the covalent character of UO2 and refute the claims about rather ionic bonding in this compound, made in some publications.