A simple two-dimensional structure was posited that aimed to capture the character of many of the qualitative findings arising from computer simulations of diffusion paths in grain boundaries. Two types of mechanism were postulated: 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 appear in the analysis of the diffusion isotope effect. Monte Carlo simulations were also made of these correlation factors. Very good agreement between the derived expressions for the correlation factors and the simulation results was found. It was possible to show that, in the absence of knowledge concerning the kinetic energy factor, 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