Energetics of cation mixing in urania-ceria solid solutions with stoichiometric oxygen concentrations.

Cation mixing energetics in urania-ceria solid solutions with stoichiometric oxygen concentrations (U(1-y)Ce(y)O(2)) have been measured by high-temperature oxide-melt drop-solution calorimetry. Measurements have been performed on eight samples with compositions spanning y = 0.119 to y = 0.815. The measured mixing enthalpies (ΔH(mix)) range from -0.6 ± 3.3 to 3.9 ± 3.0 kJ mol(-1). These values are discussed in the context of results from atomistic modeling which take into consideration the possibility of charge transfer between uranium and cerium cations to form solid solutions with mixed charge states. A comparison between measured and calculated results for ΔH(mix) suggests that such charge transfer takes place to a limited extent in the most concentrated mixtures studied.