Molecular dynamics simulation of the melting behavior of Pt-Au nanoparticles with core-shell structure

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), Pt147Au414, and Pt309Au252. The icosahedral core-shell structures, with an icosahedral Pt core covered with an icosahedral An shell, were taken as the initial configurations in this simulation. To compare with Pt-Au nanoparticles, the pure metals (Pt and An) 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 An shells, and the Pt cores always keep a typical solid state before the homogeneous melting transition. Furthermore, the extent of the premelting of the An 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 An atoms in the pure metal and core-shell bimetallic nanoparticles.