High-temperature transition of uranium dioxide to the super-ion state

A microscopic model of the high-temperature (T≈2670 K) phase transition of uranium dioxide to the super-ion state is developed. It is shown that accounting for the interaction of the point defect subsystem with the electron subsystem in the mean-field approximation (where this interaction leads to significant additional screening of the charge of some of the defects) and then calculating the configurational entropy of the point defects with allowance for the actual symmetry of the UO₂ crystalline lattice affords satisfactory agreement with the available experimental data on the degree of disorder of the anion sublattice and the behavior of the specific heat of uranium dioxide in the given temperature range. Zh. éksp. Teor. Fiz. 111, 585–599 (February 1997)