Molecular Dynamics Simulation of the Melting Behavior of Pt−Au Nanoparticles with Core−Shell Structure

Abstract

Molecular dynamics (MD) simulations have been employed to investigate the melting behavior of core−shell Pt−Au nanoparticles with four different concentrations: Pt 13 Au 548, Pt 55 Au 506, Pt 147 Au 414, and Pt 309 Au 252 . The icosahedral core−shell structures, with an icosahedral Pt core covered with an icosahedral Au shell, were taken as the initial configurations in this simulation. To compare with Pt−Au nanoparticles, the pure metals (Pt and Au) with the same particle size were also studied here. The results demonstrate that the core−shell bimetallic nanoparticles exhibit a two-stage melting, and their melting points rise as the concentration of Pt increases. A detailed analysis of the melting processes indicates that the premelting nature of the pure metal nanoparticles does not purely correspond to the surface premelting, but all atoms even including the center atom contribute to the premelting behavior through interlayer diffusion. For all the core−shell structures investigated, however, the premelting only occurs at the Au shells, and the Pt cores always keep a typical solid state before the homogeneous melting transition. Furthermore, the extent of the premelting of the Au shell is suppressed as the size of Pt core increases. The difference in the melting mechanism can be explained on the basis of the distribution of potential energy between the Pt and Au atoms in the pure metal and core−shell bimetallic nanoparticles.