# Fingerprinting Uranium Oxides with Electron Energy Loss Spectroscopy Supported by Theoretical Computations

## TL;DR

This paper shows how to identify different uranium oxide phases using electron energy loss spectroscopy and theoretical calculations.

## Contribution

The study demonstrates that O K-edge EELS can reliably distinguish uranium oxide phases despite beam damage.

## Key findings

- O K-edge EELS spectra show excellent agreement between theory and experiment for uranium oxides.
- U N-edge features are less useful for distinguishing uranium phases due to complex electronic effects.
- Low-dose experimental methods minimize beam damage and enable valence state discrimination.

## Abstract

Uranium
oxides occur in a variety of phases that differ
in their
crystal structure and uranium oxidation states. Electron energy loss
spectroscopy (EELS) is one of the few techniques that has sufficient
spatial resolution and sensitivity to electronic structure to distinguish
among phases at the nanoscale. However, beam-sensitive materials,
such as uranium oxides, are subject to spectral modification due to
interactions with the electron beam. Therefore, theory support is
essential to reliably exclude the impact of beam damage and generate
true reference data sets. Here, we use a comparison of theoretical
and experimental spectra to probe the impact of beam damage on the
O K-edge and U N-edge (N
6,7 and N
4,5) EELS spectra
of various single-valent and mixed-valence uranium oxide bulk phases.
Using a low-dose experimental setup, we show that the K-edge theoretical spectra are in excellent agreement with experiment
for both peak positions and relative intensities of respective peaks.
In contrast, U N-edge features are less distinguishing
due to the partially localized nature of the U 5f orbitals and overlapping
multiplet and spin–orbit coupling effects. This work demonstrates
that O K-edge EELS is sufficiently diagnostic to
distinguish a wide range of uranium oxides and that the experimental
approach used here minimizes beam damage and allows valence state
discrimination across the U­(IV), U­(V), and U­(VI) series. When combined
with imaging modes available in electron microscopy, this work enables
a detailed investigation and characterization of uranium redox transformations
at the nanoscale.