Radiation damage in ion-irradiated CeO$_2$ and (Ce, Gd)O$_2$ sinters: effect of the Gd content
Résumé
The radiation damage induced in cerium dioxide CeO$_2$ and cerium-gadolinium mixed oxides (Ce, Gd)O$_{2-x}$ was studied by micro-Raman spectroscopy and diffuse UV-visible reflectance spectroscopy. Sintered samples of undoped CeO$_2$ and (Ce, Gd)O$_{2-x}$ for 1 mol% and 5 mol% of Gd$_2$O$_3$ were irradiated at room temperature with 2.5-MeV Ar$^{2+}$ and 12-MeV Ar$^{4+}$ ions up to high fluences (i.e. 5x10$^{14}$ cm$^{-2}$ and 2.1x10$^{14}$ cm$^{-2}$ respectively). The Raman spectra show that no amorphization of those oxides occurs whatsoever, regardless of the Gd content. However, the damage cross section deduced from the decay of F$_{2g}$ peak intensity versus fluence seems to decrease with the Gd$^{3+}$ content. 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% Gd$_2$O$_3$, 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 Gd$^{3+}$ ions for Ce$^{4+}$ ions is likely reducing the damage and the formation of band tails related to the formation of Ce$^{3+}$ ions by electronic excitation processes.
Domaines
Physique [physics]Origine | Fichiers produits par l'(les) auteur(s) |
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