Dynamical investigation of NinAgm(n+m=147,309,561) nanoalloys with core-shell orderings

Abstract

Abstract The structures and dynamical properties of core-shell bimetallic Ni-Ag nanoalloys varying with different sizes and compositions have been studied by using Monte Carlo and Molecular Dynamics simulations. We have considered the compositions in which the size of the core increases while the total number of atoms are fixed. In this sense, two (Ni13Ag134, Ni55Ag92), three (Ni13Ag296, Ni55Ag254, Ni147Ag162) and four (Ni13Ag548, Ni55Ag506, Ni147Ag414 and Ni309Ag252) compositions were considered for 147, 309 and 561 atoms, respectively. It is obtained that highly symmetric Mackay icosahedral structures with centered symmetric cores appear for these specific sizes and compositions. Also, smaller Ni atoms tend to occupy the core and Ag atoms prefer to segregate to surface of the nanoalloy due to its lower surface and cohesive energy. Then, obtained lowest energy structures by Basin Hopping MC simulations were used as initial configurations for melting simulations. It can be said that transitions between different chemical ordering patterns with increasing temperature are possible in this systems while they are still in the solid state. Although there are clear differences in the melting process of the compositions with increasing size of the core, for all cases, surface melting occurs indicating that the Ag shell melts before inner Ni core.