Abstract
A general method is proposed for estimating activation energies of diffusion in (amorphous) covalent solids. The parameters involved are the shear modulus, the effective area associated with a bond and the size of diffusion saddle-point doorways associated with the critical percolation pathway for diffusion in the structure. Calculations of the effective force constant for dilating the diffusion doorways in a model of amorphous silica, made using the Keating potential, are in very good agreement with the behaviour predicted by the model, and calculated activation energies for diffusion are in good agreement with experimental values for diffusion of rare gases in vitreous silica.
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