No miscibility gap in Pt-Rh binary alloys: A first-principles study

Recently, diffraction experiments and bond-order calculations gave given cause for distrust in the widely accepted phase diagram of binary Pt-Rh, suggesting it forms a solid solution below 1100 K. This is in contrast to the phase diagram published by Raub in 1959. In order to clarify this situation, we use a first-principles approach to conduct an exhaustive ground-state search and set up a cluster-expansion Hamiltonian. This allows for grand-canonical Monte-Carlo simulations in order to investigate the phase behavior. We show that the miscibility gap does not in fact exist. We also present simulated diffraction patterns extracted from the cluster-expansion Hamiltonian, which are in good agreement with experimental data.