XANES study on the valence transitions in cerium oxide nanoparticles

The aim of this work is the determination of Ce environment and valence state in cerium oxide nanoparticles prepared by the microemulsion method. X-ray absorption near-edge structure measurements at Ce L₃ edge were performed on the nanoparticles as a function of annealing temperature, ranging from 298K to 873K under air condition. The experimental results support the conclusion that Ce ion, in the investigated systems, is in trivalence state when the annealing temperature is below 473K. As the temperature increases up to 623K, the XANES spectrum shows the coexistence of Ce³⁺ and Ce⁴⁺states. When the temperature is higher than 623K, the spectra become identical to that of CeO₂ with a distinct double-peak structure, corresponding to the Ce⁴⁺ state.