Diffusion correlation effects in non-stoichiometric solids

Diffusion in lattice arrays reducible to cubic symmetry can be simulated by Monte Carlo procedures. Tracer correlation factors can be derived for diffusion mechanisms in such arrays which include simple solids with point defects and non-stoichiometric materials with complex defect structures subject to defect-defect interactions. It is shown that such interactions can substantially reduce the correlation factor. A cooperative diffusion mechanism involving Wilis 2:2:2 defect clusters in UO 2+x is shown to have a correlation factor greater than unity.