Site blocking and correlated defect motion in tracer and chemical diffusion

A method is developed for analyzing defect-diffusion coefficients. Defect diffusion is an integral part of considerations in diffusion theory for atom motion in crystals, but it has not been developed as a distinct concern in diffusion kinetics. An "alloy" of tracer and nontracer atoms occupying octahedral interstices of the fcc lattice has been used as a model to develop quantitative descriptions of site blocking, correlation, and flow effects that are all characteristic elements of defect-diffusion kinetics. Correlated walk of vacancies in and near a divacancy can be discussed using these results, and this analysis suggests a method for generalizing theoretical treatments of atom-defect and defect-defect interactions in diffusion-related phenomena.