Ionic self-diffusion of Al cations and O anions in the vitreous Al2O3 with molecular dynamics simulations

Ionic self-diffusion in the non-crystalline aluminum oxide is not well understood for the scarcity of experimental and simulation investigation. In this paper, the molecular dynamics (MD) simulation is employed to investigate the diffusion mechanism of Al cations and O anions in the vitreous Al2O3. According to the trajectories of ions, three moving modes are defined, including local vibration, fast jumping and slow collective moving. The collective motion is very important for the ionic diffusion in the vitreous configurations. The diffusion of O anions in vitreous Al2O3 is greatly enhanced attributed to the collective moving between Al cations and O anions. If the Al cations are pinned, the oxygen diffusivity drops more than three orders. The collective motion also reduces the energy barrier of diffusion, thus resulting in the non-Arrhenius effect of temperature on diffusivity.