Contribution to the study of the systems uranium oxide - lanthanoid oxide

This thesis is a contribution to the study of mixed oxides (U₁,YLn,Y)O_2+X, mainly hyper-stoichiometric where Ln is a lanthanoid as the gadolinium Gd³⁺, the erbium Er³⁺ or the cesium Ce⁴⁺. The Y domain for this study is the interval 0 to 0,6 with X values between 0,05 and +0,25. The oxygen content of solid solution in thermodynamical equilibrium have been found in conditions of oxygen potential of the oxidizing sintering. The oxidation level of the uranium ion is varying differently with the valence and the lanthanoid ratio. A crystalline and chemical study, by neutrons and X-rays diffraction, gave the layer parameters of fluorine compounds. It showed the presence of complex defects (8:12:1) or (1:0:2) in the anionic sublattice. The production, by sintering reaction, of dense pellets of solid solution in an oxidizing medium, under carbon dioxide is very difficult. Swelling phenomena appear for erbium or gadolinium content mixings. These disturbances are coming from the solid solution formation. (A.L.B.)