Irradiation-induced amorphization of UO₂ films prepared by spraying-assisted combustion synthesis

Spraying-assisted combustion synthesis with uranyl nitrate -acetylacetone -2-methoxyethanol solutions was used to prepare UO2 films on an aluminum alloy substrate. The tuning of the spraying parameters and annealing temperatures allowed the preparation of UO2 films with thicknesses varying from 10-300 nm and 5-10 nm UO2 grain size. High-resolution electron microscopy and X-ray photoelectron spectroscopy showed that increasing the annealing temperature promotes Mg diffusion from the substrate into the films. The incorporation of Mg reduced the overall crystallinity of the films. The irradiation with Ar2+ ions (1.7 MeV energy and a fluence of 2 x 1016 ions/cm2) did not degrade the quality of the films. However, the Mg content significantly influenced the irradiation-induced restructuring of the UO2 films. Irradiated films with low or no Mg content exhibit high crystallinity, and the UO2/Al interfacial layer becomes highly porous. Films with higher Mg content are mostly amorphized after irradiation. The origin of irradiation-induced amorphization was related to the formation of MgyU1-yO2 +/- xsolid solutions. Chemically complex, pore-free, and amorphous Mg-Al-O film/substrate interfacial layers enable continuous Mg diffusion during irradiation. Furthermore, the gradual increase in Mg amounts triggers irradiation-induced precipitation of a crystalline MgO-rich phase within the amorphous films.