Ni-Co bimetallic nanoparticles with core-shell, alloyed, and Janus structures explored by MD simulation

Abstract

In this study, three important morphologies of Co-Ni bimetallic nanoclusters were studied by classical molecular dynamics simulation, including core-shell, Janus, and alloyed nanoparticles. Several analysis methods were used to interpret the simulation data including caloric curves, heat capacities, common neighbor analysis, scatter plots, radial chemical distribution functions, and radial distribution functions. The results of simulations proposed a core-shell>Janus>alloyed trend for thermodynamic stabilities of the studied nanoparticles. For core-shell nanoparticles, Co@Ni nanoclusters exhibited more thermodynamic stability than Ni@Co ones due to higher cohesive energy of Ni atoms. Total mechanism of melting was found similar for all of the simulated nanoclusters in such a way that melting starts from the surface and then extends to the inner parts. However, the melting process for Janus nanoparticles demonstrated some differences for which first Co atoms start the melting and occupy the surface positions, while Ni atoms retain their ordered structure. This phenomenon leads to creation of Ni@Co-Ni core-shell nanocluster with a mixed shell region near the melting point. Also, composition effect on the stabilities of three different categories of Co-Ni nanoparticles was investigated and the results indicated that for all of them, increase of Ni composition leads to more thermodynamic stability. Another interesting result was similar stabilities of Co0.4Ni0.6 nanoalloy with Co0.4@Ni0.6 core-shell nanocluster.