Segregation of Pt_(28)Rh_(27) bimetallic nanoparticles: A first-principles study

摘要

Based on a first-principles calculation combined with the cluster expansion technique and Monte Carlo statistical simulation, the segregation behavior of a Pt_(28)Rh_(27) cuboctahedral nanoparticle is examined. From the effective cluster interaction of the nanoparticle, we see a similar weak ordering tendency inside the nanoparticle to that for Pt-Rh bulk alloy. Below the bulk melting temperature of around 1700K, we find strong Pt segregation to the surface of the nanoparticle. This is due mainly to larger Pt on-site segregation energy for surface sites than that for subsurface and core sites. In order to examine the segregation behavior of the Pt_(28)Rh_(27) nanoparticle, we find that the ordering contribution is essential, which reverses the preferable segregation between edge and (100) sites. A ground-state atomic arrangement of the Pt_(28)Rh_(27) nanoparticle at T = 0K is predicted, where all the Pt atoms are located at surface sites, particularly at the vertex site of the lowest coordination number.