Discrete and continuum energetic models were presented for an heterogeneous ordered alloy with the B2 structure. A one-dimensional Ising model in the mean-field approximation was first used, in which the interaction range was limited to the first-nearest neighbors. On the basis of this discrete model, the long-range order parameter and concentration profiles across the (100) non-conservative antiphase boundary were investigated, and the free energy and interfacial free energy were calculated. The equilibrium equations were coupled via a linear gradient term that contributed to segregation at the antiphase boundary; even in a stoichiometric compound. The degree of segregation was quantified by numerically solving the equilibrium equations, and was shown to be associated with a reduction in the interfacial free energy. The discrete model was extended to 2 dimensions, from which a continuum approximation was obtained. A 3-dimensional generalization was performed which accounted for anisotropic effects.

P.Maugis: Physical Review B, 1996, 53[9], 5276-86