A general method was proposed for the estimation of diffusion activation energies in amorphous covalent solids. The parameters which were involved were the shear modulus, the effective area that was associated with a bond, and the size of the diffusion saddle-point doorways which were associated with the critical percolation pathway for diffusion in the structure. It was found that calculations of the effective force constant for dilation of the diffusion doorways, in a model for amorphous silica, were in very good agreement with the predicted behavior of the model. Also, the calculated activation energies for diffusion were in good agreement with experimental data on the diffusion of rare gases in vitreous silica.

S.L.Chan, S.R.Elliott: Journal of Physics - Condensed Matter, 1992, 4[5], 1269-80