| Abstrakt: |
The structures and dynamical properties of core–shell bimetallic Ni-Ag nanoalloys varying with different sizes and compositions have been studied using Monte Carlo (MC) and Molecular Dynamic (MD) simulations. We have considered the compositions in which the size of the core increases while the total number of atoms is 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. Highly symmetric Mackay icosahedral structures with centred 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 the surface of the nanoalloy due to its lower surface and cohesive energy. Then, the lowest energy structures obtained by Basin Hopping MC simulations were used as initial configurations for melting simulations. The transitions between different chemical ordering patterns with increasing temperature are possible in these 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 the inner Ni core. [ABSTRACT FROM AUTHOR] |
