Transport phenomena were studied for a binary (AB) alloy on a rigid square lattice with nearest-neighbor attraction between unlike particles, assuming a small concentration cv of vacancies V being present, to which A (B) particles could jump with rates ΓA (ΓB) in the case where the nearest-neighbor attractive energy EAB was negligible in comparison with the thermal energy kT in the system. This model exhibited a continuous order-disorder transition for concentrations cA, cB =1 - cA - cV in the range cA,1crit ≤ cA ≤ cA,2crit, with cA,1crit = (1 - m* - cV)/2, cA,2crit = (1 + m* - cV)/2, m ≈ 0.25, the maximum critical temperature occurred for c = cA = cB = (1 - cV)/2; i.e., m* = 0. This phase transition belonged to the d = 2 Ising universality class, demonstrated by a finite-size scaling analysis. From a study of mean-square displacements of tagged particles, self-diffusion coefficients were deduced, while applying chemical potential gradients permitted the estimation of Onsager coefficients. Analyzing finally the decay with time of sinusoidal concentration variations that were prepared as initial condition, also the interdiffusion coefficient was obtained as function of concentration and temperature. As in the random alloy case (i.e., a non-interacting ABV model) no simple relation between self-diffusion and interdiffusion was found. Unlike this model mean-field theory could not describe interdiffusion, however, even if the necessary Onsager coefficients were estimated via simulation.

Interplay of Order-Disorder Phenomena and Diffusion in Rigid Binary Alloys in the Presence of Vacancies: Monte Carlo Simulations. A.De Virgiliis, K.Binder: Physical Review B, 2006, 73[13], 134205