Transport phenomena were studied for a binary, AB, alloy on a rigid square lattice with nearest-neighbor attraction between unlike particles. A small concentration, cv, of vacancies was assumed; to which A (B) particles could jump at the rates ΓA (ΓB) in the case where the nearest-neighbor attractive energy, EAB, was negligible in comparison with the thermal energy, kT, of 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, with the maximum critical temperature occurring for c = cA = cB = (1−cV)∕2. That is, m*=0. This phase transition belonged to the d = 2 Ising universality class, as demonstrated by a finite-size scaling analysis. From a study of the mean-square displacements of tagged particles, self-diffusion coefficients were deduced; while applying chemical potential gradients permitted an estimation to be made of the Onsager coefficients. Finally, by analyzing the time-decay of initial sinusoidal concentration variations, the interdiffusion coefficient was also obtained as functions of concentration and temperature. As in the random-alloy case (non-interacting ABV model) no simple relationship was found between self-diffusion and interdiffusion. Unlike this model, mean-field theory could not describe interdiffusion 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 (15pp)