Mass transport in an ordered three-dimensional lattice-gas system

Abstract

Diffusion phenomena on a three-dimensional discrete lattice are studied both analytically and by means of computer simulations. The case of repulsive interaction between the particles occupying nearest-neighbor lattice sites is considered. It is shown that in the case of the disordered particle arrangement, transport phenomena can be described within a theory based on the assumption of uncorrelated particle jumps. In contrast, strong correlation in particle motion, which takes place in antiferromagnetically ordered systems results in considerably lowering the diffusion coefficients. Both random walks and generation-recombination processes of ``structural defects'' of the ordered state govern mass transport in this case. It is shown that jumps of individual defects (vacancies and excess particles of the almost filled and empty sublattices, respectively) and dimers contribute to mass flow. In the vicinity of stoichiometric concentration the defect jumps accompanied with their recombination may also contribute significantly. The jump and collective diffusion coefficients are derived analytically. Comparison of the analytical forms with Monte Carlo data shows a good agreement.