Stability and ordering properties of fcc alloys based on Rh, Ir, Pd, and Pt

Stability properties and ordering trends for the six face-centered cubic binary combinations of the four transition metals Rh, Ir, Pd, and Pt are examined in the context of electronic structure calculations. The method is based on a Green's function description of the electronic structure of random alloys. Configurational order is treated within the generalized perturbation method. On one hand, the three alloys Pd-Rh, Pd-Ir, and Pt-Ir that have been studied experimentally are confirmed to behave like phase-separating systems. On the other hand, the other three mixtures Pd-Pt, Rh-Ir, and Pt-Rh, for which phase-separating trends have been inferred from experiments, are found to display chemical order with ordering of the (1 0 0) and (1 1/2 0) family types and a mixture of both, respectively. The origin of these results is discussed in terms of electronic structure properties.