A generalized quasichemical approximation and a cluster-energy model are used to study the phase diagram and local correlations in pseudobinary alloys. The calculated liquidus-solidus curves for ${\mathrm{In}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$P, ${\mathrm{In}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ga}}_{\mathrm{x}}$As, and ${\mathrm{InSb}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{As}}_{\mathrm{x}}$ are in good agreement with experiment. Accurate bond-length distributions and normal spinodal order-disorder transition curves are also obtained. Other models that replicate recently predicted multivalley spinodal decomposition are shown to produce poor liquidus-solidus curves.

• Received 8 June 1987

DOI:https://doi.org/10.1103/PhysRevB.36.6585