Epitaxial Effects on Coherent Phase Diagrams of Alloys

Using a cluster description of a coherent binary alloy, we predict and contrast bulk and epitaxial composition-temperature phase diagrams. For alloys with stable ordered compounds in bulk, epitaxial growth away from the lattice-matched composition distorts phase boundaries and changes ordering temperatures. For alloys insoluble in bulk below a miscibility-gap temperature $T_{\mathrm{MG}}$, the epitaxial alloy may remain stable to temperatures > 1200 K below $T_{\mathrm{MG}}$ even on lattice-matched substrates, with stoichiometric compounds possible at low temperature.