Lattice dynamics and molecular dynamics studies of the oxides UO2 and Li2O in their normal as well as superionic phases were reported. Lattice dynamics calculations were carried out using a shell model in the quasi-harmonic approximation. The calculated elastic constants, phonon frequencies and specific heat were in good agreement with reported experimental data, which help validate the interatomic potentials required for undertaking molecular dynamics simulations. The calculated free energies reveal high pressure fluorite to cotunnite phase transitions at 70GPa for UO2 and an anti-fluorite to anti-cotunnite phase transformation at 25GPa for Li2O, in agreement with reported experiments.

Molecular dynamics studies provide important insights into the mechanisms of diffusion and superionic behaviour at high temperatures. The calculated superionic transition temperature of Li2O was 1000K, while that of UO2 was 2300K.

Fast Ion Diffusion, Superionic Conductivity and Phase Transitions of the Nuclear Materials UO2 and Li2O. P.Goel, N.Choudhury, S.L.Chaplot: Journal of Physics - Condensed Matter,  2007, 19[38], 386239 (8pp)