A new description was presented of concentration-dependent ion exchange. A 3-dimensional quasi-chemical approximation was used to estimate the chemical potentials of the exchanging cations. The diffusion coefficient was then expressed as a function of the self-diffusion coefficients, excess interaction energy and cation-cation coordination. The modified quasi-chemical description resulted in excellent fits to experimentally determined concentration-dependent diffusion coefficients. It was shown to be useful for modelling the strong concentration-dependence of ion exchange, as used in the development of glasses for gradient-index optics.

J.M.Inman, J.L.Bentley, S.N.Houde-Walter: Journal of Non-Crystalline Solids, 1995, 191[1-2], 209-15