Modelling of the formation of Pd-Ni alloy nanoparticles by interdiffusion

Long–time scale molecular dynamics simulation in combination with the embedded atom method is used to investigate the effect of surface segregation phenomena at 1000 K on the structure of Pd alloy nanoparticles (of diameter of ~ 4.5 nm) containing ~ 30 at. % Ni. A core–shell f.c.c. structure was chosen as the initial state wherein a core of Ni atoms is surrounded by shell of Pd atoms. It is found that such nanoparticles form a surface–sandwich structure by interdiffusion. In this structure, the Ni atoms, which mostly accumulate in a layer just below the surface and at the same time are located in the centres of interpenetrating icosahedra to generate a subsurface shell as a Kagomé net. Meanwhile, the Pd atoms occupy the vertices of the icosahedra and cover this Ni layer from inside and outside as well as being located in the core of the nanoparticle forming (according to alloy composition) a Pd–rich solid solution with the remaining Ni atoms. The total atomic fraction involved in building up the shell of the nanoparticle in the form of the Ni Kagomé net layer covered on both side by Pd atoms can be estimated at ~ 70 %.