Resonant x-ray spectroscopy of uranium intermetallics at the M4,5 edges of uranium

Abstract

We present resonant x-ray emission spectroscopic (RXES) data from the uranium intermetallics UPd3, USb, USn3 and URu2Si2 at the U M4,5 edges and compare the data to those from the well-localized 5f 2 semiconductor UO2. The technique is especially sensitive to any oxidation of the surface, and this was found on the USb sample, thus preventing a good comparison with a material known to be 5f 3 . We have found a small energy shift between UO2 and UPd3, both known to have localized 5f 2 configurations, which we ascribe to the effect of conduction electrons in UPd3. The spectra from UPd3 and URu2Si2 are similar, strongly suggesting a predominant 5f 2 configuration for URu2Si2. The valence-band resonant inelastic x-ray scattering (RIXS) provides information on the U P3 transitions (at about 18 eV) between the U 5f and U 6p states, as well as transitions of between 3 and 7 eV from the valence band into the unoccupied 5f states. These transitions are primarily involving mixed ligand states (O 2p or Pd, Ru 4d) and U 5f states. Calculations are able to reproduce both these low-energy transitions reasonably well.

Relevance of formation conditions to the size, morphology and local structure of intrinsic plutonium colloids

“…5a are not significant enough to be interpreted; the use of high resolution XANES techniques such as HERFD (High Energy Resolution Fluorescence Detection) as well as M edge measurements might provide further information. 50,[54][55][56] Nevertheless, the used experimental conditions and the thorough inspection of our spectra at this stage suggest the very strong predominance of (+IV) oxidation state for plutonium in the colloid samples (the exclusive presence of Pu(IV) cannot be affirmed from sole Pu L III edge XANES spectra). Fig.…”

The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO2

“…Despite the observation that the f‐DOSs calculated by FDMNES are in good agreement with experimental data, the simulated XANES (see Figure 6 d) calculated once the spin–orbit effect is added completely disregards part of the f‐DOS and peak B is not reproduced. The difference between the f‐DOS and simulated XANES stems from the selection rules, which allow transitions only to states with j =5/2 for M 4 , whereas transitions to both j =5/2 and j =7/2 states are allowed for M 5 [63] . Figure S6 in the Supporting Information allows comparison of the simulations of M 4 and M 5 .…”

Separate measurement of the 5f5/2 and 5f7/2 unoccupied density of states of UO2

“…The experiments were performed on Beamline as also observed by Kvashnina et al [19,27]. This sensitivity is due to the very intense x-ray absorption cross sections for U M-edges (for instance, the x-ray probing depth across the intense M 4 /M 5 white lines can be less than 100 nm) and the propensity for uranium to react with oxygen.…”