Reversal segregation driven by lattice vibration for alloy nanoparticles

Based on a first-principles calculation, the effects of lattice vibration on the segregation behavior of Pt–Rh alloy nanoparticles is examined. Pt atoms naturally have lower vibrational free energy for sites with lower coordination number, while Rh atoms neighboring to the Pt atoms also have lower vibrational free energy with respect to Rh metal nanoparticles. Due to the substantial decrease in vibrational free energy for the Rh atoms neighboring Pt at the core site, lattice vibration increases the Pt on-site segregation energy from the core site to subsurface or surface sites. A significant difference in the temperature dependence of the on-site segregation energy between vertex and edge sites would lead to a reversal of segregation induced by lattice vibration, which is confirmed by cluster expansion and Monte Carlo statistical simulation.