A theory of diffusion in the ordered alloy .3. Chemical diffusion

In this study a simple model of a long range ordered alloy, in which the sublattics exist a priori, is considered for the purposes of describing chemical diffusion. Diffusion is assumed to take place via the agency of vacancies. Four atom-vacancy exchange frequencies are specificed. Manning's formalism for describing diffusion in the random alloy is adapted and extended to the present model. The thermodynamic factors are calculated by adapting the Widom formalism. The average jump frequencies and thermodynamic factors are calculated exactly; the calculated collective correlation factors, which appear in combination in the vacancy wind terms in the intrinsic diffusivities, are found to be in good agreement with Monte Carlo computer simulation results which are also presented.