Calculation and simulation of chemical-diffusion coefficients: The inadequacy of the mean-field theory

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Abstract
Initial chemical-interdiffusion coefficients in a simple cubic, random, binary alloy, Ising model have been determined analytically and by Monte Carlo simulations, using chemical rate equations for atomic exchanges. The results, obtained as a function of the composition gradient, enthalpy of mixing, and temperature, show that the chemical enhancement of the diffusion coefficients saturates and is considerably lower than predicted by Darken’s equation. The discrepancy is due to the inadequacy of the mean-field theory and linear-response approximation at high enthalpies of mixing.