Study of structures and thermodynamics of CuNi nanoalloys using a new DFT-fitted atomistic potential

Abstract

Shape, stability and chemical ordering patterns of CuNi nanoalloys are studied as a function of size, composition and temperature. A new parametrization of an atomistic potential for CuNi is developed on the basis of ab initio calculations. The potential is validated against experimental bulk properties, and ab initio results for nanoalloys of sizes up to 147 atoms and for surface alloys. The potential is used to determine the chemical ordering patterns of nanoparticles with diameters of up to 3 nm and different structural motifs (decahedra, truncated octahedra and icosahedra), both in the ground state and in a wide range of temperatures. The results show that the two elements do not intermix in the ground state, but there is a disordering towards solid-solution patterns in the core starting from room temperature. This order-disorder transition presents different characteristics in the icosahedral, decahedral and fcc nanoalloys.

Core–Shell versus Other Structures in Binary Cu38–nMn Nanoclusters (M = Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au; n = 1, 2, and 6): Theoretical Insight into Determining Factors

“…Based on these results, we concluded that vacancies in the d shell, the deformation energy of the Cu 32 shell, and the cohesive energy of the M 6 core are useful for discussing and predicting the Cu 32 M 6 structure. − These factors also play important roles in determining the structure and stability of other combinations of two metal elements; for instance, the present results suggest that the Cu–Ni binary metal cluster has a core–shell structure with Ni atoms in the core because Ni has a d 8 s 2 electron configuration. Indeed, a theoretical study using the Gupta potential reported that such a core–shell structure is stable . In discussing very large metal clusters/particles, however, the results for the relatively small systems considered here are not very useful, and the factors discussed are insufficient because some other factors such as the size-mismatching effect and the size dependency of the cohesive energy become more important.…”

Tunable Magnetism in Nanoporous CuNi Alloys by Reversible Voltage‐Driven Element‐Selective Redox Processes

“…It is known that the Cu–Ni bulk alloys present a miscibility gap for temperatures below 600 K . However, in recent works, it is suggested that in nanoparticles with sizes below 10 nm, the driving forces dominating segregation are much weaker, thus eventually lowering the miscibility gap to below room temperature . Hence, it is a plausible hypothesis that the metallic Cu obtained for negative voltages gets dissolved again in the Cu–Ni solid solution at room temperature owing to the narrow pore walls and the high surface area‐to‐volume ratio of the investigated material.…”

Thermal properties and segregation phenomena in transition metals and alloys: modeling based on modified cohesive-energies

“…A last case demonstrating the problematic use of cohesiveenergies instead of actual solid-state interatomic bond-energies involves modeling of phase segregation and transition temperatures in Cu-Ni truncated-octahedra. Previous studies that focused on few overall compositions only [6,37,38] predicted an asymmetric off-centre Cu/Ni Janus-like compositional configuration (JA) as the most stable at relatively low temper atures, which was found also by STEM/EDX measurements [39]. Indeed, according to our preliminary FCEM/ CBEV computations that involve fewer concentration variables when combined with the coarse-grained layer model, CGLM [40], this configuration is obtained for almost all compositions (excluding the very dilute ones) when the bondenergies of Cu and of Ni are used as input (E b , table 1).…”