The O diffusivity was studied by using the molecular dynamics method in the transition range up to the super-ionic state (melting of the O sub-lattice), and near to the melting point. The temperature dependence of the diffusion coefficient of a doubly-charged O ion was deduced. In the crystalline state, at 1800 to 2600K, this dependence was described by an exponential dependence; with a diffusion activation energy of 2.6eV. In the super-ionic state (2600 to 3100K), the activation energy for diffusion of an O anion decreased to 1.88eV. In the melt (3100 to 3600K), the exponential dependence of the diffusion coefficient of O2– persisted; but the activation energy for diffusion further decreased to 0.8eV. The present experimental results agreed (within experimental error) with published data on O diffusion in the crystalline phase.

Oxygen Diffusion in Uranium Dioxide in the Temperature Range of Phase Transitions. A.Y.Kupryazhkin, A.N.Zhiganov, D.V.Risovanyĭ, V.D.Risovanyĭ, V.N.Golovanov: Technical Physics, 2004, 49[2], 254-7