Atomistic simulation of a superionic transition in UO$_2$

The results of the atomistic simulation of a superionic transition and melting of uranium dioxide are presented. The temperature dependences of the concentration of defects in the oxygen sublattice and changes in the heat capacity and isothermal compressibility upon the superionic transition are calculated. It is shown that the curve of the superionic transition in the $PT$ diagram can be described by the Ehrenfest’s equation. The possibility of describing the superionic transition within the framework of the theory of second- order phase transitions is discussed. Based on the results obtained, it is considered that this structural transformation can occur in other materials.