Phase equilibria and ordering in solid Pt-Rh calculated by means of a refined bond-order simulation mixing model

The equilibrium phase diagram of solid Pt-Rh is calculated by means of semi-grand canonical lattice Monte Carlo simulations using thermodynamic integration. Configurational energies are described by a refined BOS model (bond-order simulation mixing), which is fitted to reference data obtained from first-principles calculations. The calculated equilibrium phase diagram shows the ordered face-centered cubic structure 40 and D022 structure as stable phases at low temperatures (<250 K) and has no miscibility gap at higher temperatures, which is in contrast to existing assumptions. The calculated short-range order parameters of the solid solution are in full agreement with experimental values and thus confirm that the BOS model provides a sound description of configurational energies.