a Department of Geology, Arizona State University, Tempe, AZ 85287-1404, USA
b Department of Chemistry/Biochemistry, Arizona State University, Tempe, AZ 85287, USA
Abstract:
We followed the reduction of Ce4+ in CeO2 by observing changes in the shape of the Ce M4,5 edge by parallel electron energy-loss spectroscopy with a transmission electron microscope. The energy-loss near-edge structure of the beam-damaged CeO2 exhibits Ce M4,5 and O K-edge shapes that are consistent with reduction to a Ce3+ oxide. During the damage process the spectrum of CeO2 changes as follows: (a) decreases in energies of the M5 and M4 maxima; (b) changes in shape of the near-edge structure; (c) inversion of the M5 to M4 branching ratio; and (d) increase in the M5 to M4 area ratio. We simulated M4,5 edges of damaged CeO2 with a linear combination of Ce4+ and Ce3+ spectra and observed no intermediate oxidation states.