A simple 2-dimensional structure was proposed that attempted to capture the character of many of the qualitative findings from computer simulations of diffusion paths in grain boundaries. Two types of mechanism were posited: those where single atom jumps occurred and those where multiple atom jumps occurred. Analytical expressions were derived for the tracer correlation factors; including those correlation factors that appeared in the analysis of the diffusion isotope effect. Monte Carlo simulations of these correlation factors were also carrier out. Very good agreement was found between the derived expressions for the correlation factors and the simulation results. It was possible to show that, in the absence of any knowledge concerning the kinetic energy factor AK, isotope effect experiments could not differentiate between a simple atom-jump mechanism and a multiple-atom jump mechanism.

Correlated Tracer Diffusion in an Ordered Interface Structure. I.V.Belova, G.E.Murch: Philosophical Magazine, 2003, 83[20], 2399-407