Thermodynamics on UO2-ZrO2-LnOsub(2-x) solid solutions

This work was directed to establish the stability and the equilibrium oxygen partial pressure of solid solutions between UO2, ZrO2 and the oxides of the lanthanides (LnOsub(2-x)). The oxygen potential of the mixed oxides was determined by the EMF-method. Both solid Fe+FeO and dry air electrodes were used as reference. The results indicate that the uranium substitution by zirconium and the lanthanides in the U-Zr-Ln mixed oxides stabilizes the higher ''uranium valancies'' by increasing the oxygen solubility in these solid solutions under a given oxygen partial pressure. The strength of this stabilization increases in the order of Zr, Nd, Ce, La substitutions. The difference in the stabilization of mean uranium vacancies can also be interpreted in terms of the difference in the lattice parameter of the solid solutions. (orig.)