On the high temperature transition in UO2

Within the framework of the phenomenological theory, from the general symmetry point of view, the transition into the superionic state in crystals with a fluorite structure is studied. The Landau Hamiltonian defined in this paper restricts significantly options for microscopic models to describe the transition. The nature of the observed anomalies of heat capacity and diffusion coefficient could be explained within the proposed phenomenological consideration. (orig.)