Nanoalloys of Metals Which Do Not Form Bulk Alloys: The Case of Ag–Co

Abstract

Ag and Co metals do not form macroscopic solid or liquid alloys. However, Ag m Co n clusters have been produced in dual-target dual-laser vaporization experiments, and the same occurs for other pairs of immiscible metals. We have performed density functional calculations to shed light on this phenomenon. The main result, obtained for clusters with sizes m + n not larger than 11, is that the cohesive energies justify that those clusters can be formed starting from free Ag and Co atoms, which is the case in the vaporization experiments. At the same time, mixing of Ag and Co is difficult even at the nanoscale. This is revealed by the application of several miscibility criteria. Those two features become, nevertheless, compatible in the clusters. Even if the cluster sizes considered are small, the emerging trend becomes clear: Co atoms form a core in the inner part, surrounded by a shell of Ag atoms on the surface. A consequence is that core–shell clusters can be formed from pairs of metals that do not form macroscopic alloys. The magnetic moments μ of the Ag m Co n clusters are due mainly to the Co atoms, and the presence of Ag induces a reduction in the magnitude of μ.

C60Con complexes as hydrogen adsorbing materials

“…The lowest energy structures obtained for free Con clusters are as follows: Co3 is a triangle, Co4 is a tetrahedron, Co5 is a square pyramid, Co6 is an octahedron, Co7 is a face-capped octahedron, and Co8 is a bi-capped octahedron. These results are in good agreement with previous studies [43][44][45]. As discussed by Ma et al [45], Co5 has two competing isomers with similar energy, the square pyramid and a trigonal bipyramid, and different studies predict one or the other as the lowest energy structure (a small distortion of the first structure leads to the second).…”

Computational Characterization of the Intermixing of Iron Triade (Fe, Co, and Ni) Surfaces and Sub-nanometric Clusters with Atomic Gold

“…Our results are consistent with a recent work 50 showing that core−shell clusters can be formed from pairs of metals (Co and Ag) that do not form macroscopic alloys. Similarly, we have found that the replacement of atomic gold by a Ni atom is highly endothermic at extended gold surfaces (1.59 eV), whereas it becomes exothermic for all triade atoms in 13-atom gold clusters (see Table 3).…”

The geometry, electronic and magnetic properties of Zr n Ni (n = 2-14) clusters: A first-principles jointed particle-swarm-optimization investigation

“…P. Marin et al [56] and A. Gomez Herranz et al [58] found out the reason for quenching of magnetic moments in these binary transition-metal clusters. The spatial spin density distribution of Zr n Ni clusters is also obtained (shown in figure 4).…”