Diffusion coefficient of foreign particles in glassforming melts

A model of diffusion accounting for a distribution of barriers heights is developed. It is demonstrated that activation energy of diffusion depends on the maximal height of barrier that is to be overcome, not on the average height of barriers. The temperature dependence of diffusivity (respectively of ion conductivity) declines from strict Arrhenius behavior, although the declination is not as strong as in the case of shear viscosity. As the determination of the maximal height of the barriers that must be overcome is a percolation problem, diffusion to short (in molecular scale) distances is at ease as compared to diffusion to macroscopic distances.