Thin films of uranium cerium mixed oxides U_xCe_1−xO_2±y have been prepared by DC sputtering and characterized by X-ray photoelectron spectroscopy (XPS). Reduction and oxidation properties were analysed by exposing the films to atomic hydrogen and to atomic oxygen, respectively. Possible interaction between uranium and cerium were investigated by comparing the compounds to the single oxides of cerium and uranium. Uranium seems to promote the reduction of cerium. Conversely cerium promotes oxidation of uranium. Under our deposition conditions, it was not possible to produce pure U(IV) together with pure Ce(IV). The synthesis of U₂O₅ with U(V) cannot be obtained directly by DC sputtering, whereas with addition of cerium, U(V) seems to be stabilized and obtained more easily. This can be related to a charge transfer between Ce(IV) and U(IV).

Thin films of U_1− xTh_xO₂ (x = 0 to 1) have been deposited via reactive DC sputter technique and characterized by X-ray/Ultra-violet Photoelectron Spectroscopy (XPS/UPS), X-ray Powder Diffractometer (XRD) and Cyclic Voltammetry (CV) in order to understand the effect of Thorium on the oxidation mechanism. During the deposition, the competition between uranium and thorium for oxidation showed that thorium has a much higher affinity for oxygen. Deposition conditions, time and temperature were also the subject of this study, to look at the homogeneity and the stability of the films. While core level and valence band spectra were not altered by the time of deposition, temperature was affecting the oxidation state of uranium and the valence band due to the mobility increase of oxygen through the film. X-ray diffraction patterns, core level spectra obtained for U_1 − xTh_xO₂ versus the composition showed that lattice parameters follow the Vegard's law and together with the binding energies of U-4f and Th-4f are in good agreement with literature data obtained on bulk compounds. To study the effect of thorium on the oxidation of U_1 − xTh_xO₂ films, we used CV experiments at neutral pH of a NaCl solution in contact with air. The results indicated that thorium has an effect on the uranium oxidation as demonstrated by the decrease of the current of the oxidation peak of uranium. XPS measurements made before and after the CV, showed a relative enrichment of thorium at the extent of uranium at the surface supporting the formation at a longer term of a thorium protective layer at the surface of uranium-thorium mixed oxide.