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_4,5 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_4,5 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 M_4,5 edges of damaged CeO₂ with a linear combination of Ce⁴⁺ and Ce³⁺ spectra and observed no intermediate oxidation states.