Radiation damage in ion-irradiated CeO2 and (Ce, Gd)O2 sinters: Effect of the Gd content

The radiation damage induced in cerium dioxide CeO2 and cerium-gadolinium mixed oxides (Ce, Gd)O2-x was studied by micro-Raman spectroscopy and diffuse UV-visible reflectance spectroscopy. Sintered samples of undoped CeO2 and (Ce, Gd)O2-x for 1 mol% and 5 mol% of Gd2O3 were irradiated at room temperature with 2.5-MeV Ar2+ and 12-MeV Ar4+ ions up to high fluences (i.e. 5 × 1014 cm−2 and 2.1 × 1014 cm−2 respectively). The Raman spectra show that no amorphization of those oxides occurs whatsoever, regardless of the Gd content. No clear change of the damage cross section with the Gd3+ content is deduced from the decay of F2g peak intensity versus fluence. Moreover, the reflectivity spectra show a clear decrease of the band-gap energy and increase of the Urbach energy arising from point defect accumulation. Similar effects are found for 1 mol% and 5 mol% Gd2O3, whereas a larger effect on band tailing is seen for undoped ceria. The respective roles of nuclear collisions and electronic excitations are discussed for both ion energies knowing that the two kinds of measurements do not probe the same sample depth. The substitution of Gd3+ ions for Ce4+ ions is likely reducing the damage and the formation of band tails related to the formation of Ce3+ ions by electronic excitation processes.