Molecular dynamics study of Frenkel pair recombinations in fluorite type compounds

The recombination behaviors of cation and anion Frenkel pairs have been investigated in four fluorite structure compounds: Li2O, CaF2, CeO2 and UO2. The calculations have been done in the framework of empirical potentials molecular dynamics simulations. They have revealed that the recombination processes are strongly dependent on the configuration (i.e. the sublattice, the distance between the Frenkel pairs and the local topology of the interstitials). Each configuration shows the same recombination process whatever the chemistry (i.e. for the four compounds Li2O, CaF2, CeO2 and UO2), such that the recombination processes are related to the crystal structure of the materials. Two different recombination regimes have been identified: either spontaneous (i.e. temperature independent) or thermally activated. The recombinations are direct or occur through replacement sequences.