A modification of the well-known Maxwell-Garnett equation for the mobility (effective diffusion coefficient) in 2-phase media (matrix with inclusions) was suggested. It permitted the description of a wide range of experimental situations. This novel approach correctly treated the partial trapping of a diffusing particle by an inclusion, as well as the effect of an energy barrier to particle penetration into an inclusion. Computer simulations showed that the present mean-field theory reproduced well the results for square inclusions, without any concentration limitation. In the case of inclusions having other shapes (such as spheres), the theory applied well up to concentrations where mobile particles became trapped in so-called pockets between inclusions.

Calculations of the Effective Diffusion Coefficient for Inhomogeneous Media. J.R.Kalnin, E.A.Kotomin, J.Maier: Journal of Physics and Chemistry of Solids, 2002, 63[3], 449-56