- To construct the thermodynamical potential of an ordering alloy the pseudopotential method is applied. The conditions of the intermediate phase formation are studied in systems with limited solubility. Possible reasons for a narrow homogeneity region of these phases are established. An analysis is made of the dependence of phase equilibrium on composition and temperature. Numerical calculations are given for the BaCd system, having a b.c.c. lattice. [Russian Text Ignored].