A study was made of proton diffusion, in amorphous SiO2, from the atomic scale to the long-range percolative regime. Ab initio molecular dynamics results suggested that the predominant atomic process consisted of cross-ring inter-O hopping assisted by network vibrations. A statistical analysis which accounted for the disorder in amorphous SiO2 yielded relationships between transition energies and inter-O distances for both cross-ring and nearest-neighbor hopping. The percolative regime was then studied by using large-scale model systems to reproduce these relationships. Cross-ring hopping was confirmed to be the predominant diffusion mechanism; a conclusion which was supported by a good agreement with experiment with regard to the activation energy.

Proton Diffusion Mechanism in Amorphous SiO2. J.Godet, A.Pasquarello: Physical Review Letters, 2006, 97[15], 155901 (3pp)