A DEFECT STRUCTURE STUDY OF NONSTOICHIOMETRIC URANIUM-DIOXIDE BY STATISTICAL-MECHANICAL MODELS

In order to clarify the defect structure of UO2+x, two types of defect clusters, the 2:2:2 cluster and the cuboctahedral cluster, are explor ed by comparing the oxygen potential and the partial molar enthalpy of oxygen calculated from the statistical-mechanical model formulated fo r each cluster with the measured ones. The model for the cuboctahedral clusters in equilibrium between various charge states gives good agre ements with both the oxygen potential and the partial molar enthalpy o f oxygen, whereas the models of the clusters which assume a single cha rge state do not.