Complex atomic-diffusion mechanism in ionic superconductors: The case of the lithium-oxide antifluorite

In this molecular-dynamics study performed in the superionic phase of Li2O, we have investigated the fast-diffusion process. The calculated concentration of cationic Frenkel-pairs is in good agreement with the experimental data. A few of these defects are dissociated and contribute to diffusion, whereas the major part quickly recombines. The analysis of the cation trajectories has allowed us to identify three types of discrete jumps characterised by their length. The nearest-neighbour jumps are dominant and follow two different migration paths. A quantitative analysis, including the calculation of the atomic jump frequencies, has been carried out. The cations spend most of the time on regular lattice-sites. The combination of the various jumps results in a complex migration mechanism and the corresponding effective activation-enthalpy has been determined. All the results provide an extended view of the atomic-diffusion process in a superionic conductor.