Electrical conductivity and defect structure of (U,Pu)O2+x

The electrical conductivities of (U1-yPuy)O2+x (y=0.05, 0.10, 0.20 and 0.50) were measured by the four inserted wires method in the oxygen partial pressure range from 10-13 to 10-1.5 Pa at 1273 K. From the oxygen partial pressure dependence of the electrical conductivity, the defect structure of (U1-yPuy)O2+x was discussed with the complex defect model consisting of oxygen vacancies and two kinds of interstitial oxygens. Two types of the temperature dependence of the electrical conductivity at constant composition were observed: One is Z-type behavior with lower activation energy in the composition with larger deviation from the stoichiometry, and the other is L-type behavior with higher activation energy at nearly stoichiometric composition. The conduction mechanism in (U1-yPuy)O2+x with Z-type behavior can be explained by a hopping model between U4+ and U5+ ions, but the same model can not be applied to the L-type conduction. It was shown that the two types of the conduction behavior are closely related to their defect structures. (orig.)