Diffusion kinetics of isolated and paired species: a Monte Carlo study

Abstract

In this paper, we address a four-frequency diffusion model that allows diffusion of paired and unpaired atoms (or small molecular species) in an otherwise empty lattice. The model is useful for describing tracer and collective diffusion of interstitials in dilute interstitial solid solutions and of adsorbed species on surfaces. Diffusion kinetics of this model have been treated analytically by McKee, Le Claire and Okamura and Allnatt. We use Monte Carlo computer simulation to calculate, for the first time, the correlation factors and the linear solute diffusion enhancement factor. Absolute values of the tracer correlation factors and the linear enhancement factors are in excellent agreement with the results of the theory of Okamura and Allnatt, but only in semi-quantitative agreement with results of the other theory. A general argument is also presented to show that the chemical diffusion coefficient does not exhibit correlation effects. This is verified by computer simulation.