In-plane chemical pressure in (U1−yCey)O2 studied by Raman spectroscopy

We investigate the nature of bonding and charge states in (U1−yCey)O2 (y = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) by Raman spectroscopy. Raman spectrum of UO2 exhibits two prominent bands below 1000 cm−1, a F2g mode at 446 cm−1 and a F1u LO mode at 578 cm−1. As y is increased from 0 to 0.6, the F1u exhibits a large blue shift of 90 cm−1, and from y = 0.6 to 1.0, a red shift of 54 cm−1. We show that our results can be interpreted as arising from anisotropic compression/relaxation of the lattice under Ce substitution and this can give an indication of its charge states. Alternate interpretations have been given in the literature on the effect of substituents and dopants to the Raman spectra of UO2 and CeO2. The present interpretation of chemical stress effects can be taken as another plausible explanation.