Determination of Ce4+/Ce3+ in electron-beam-damaged CeO2 by electron energy-loss spectroscopy

We followed the reduction of Ce4+ in CeO2 by observing changes in the shape of the Ce M-4,M-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 M-4,M-5, and O K-edge shapes that are con sistent with reduction to a Ce3+ oxide. During the damage process the spect rum of CeO2 changes as follows: (a) decreases in energies of the M-5 and M- 4 maxima; (b) changes in shape of the near-edge structure; (c) inversion of the M-5 to M-4 branching ratio; and (d) increase in the M-5 to M-4 area ra tio. We simulated M-4,M-5 edges of damaged CeO2 with a linear combination o f Ce4+ and Ce3+ spectra and observed no intermediate oxidation states. (C) 1999 Elsevier Science Ltd. All rights reserved.