Cu–Ni nano-alloy: mixed, core–shell or Janus nano-particle?

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.

“…13, where some degree of intermixing is usually found. This intermixing may be caused by temperature effects.…”

Section: Thermodynamic Stability Of Segregationmentioning

confidence: 98%

Section: Thermodynamic Stability Of Segregationmentioning

confidence: 99%

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

Panizon

Olmos-Asar

Peressi

et al. 2015

“…Nonetheless, this effect is small, and this is in agreement with the predictions made for similarly shaped PtPd nanoparticles with a radius of 4 nm. 8,9,53 We would like to stress that if a structure is very unfavourable for a given chemical composition, it will rearrange toward a more stable shape before melting. We have found that the thermodynamic approach gives important and useful insights into the thermal behaviour of nanoparticles with a radius above 3-4 nm.…”

Section: Discussionmentioning

confidence: 99%

Multiscale approach for studying melting transitions in CuPt nanoparticles

Pavan

Baletto

Novaković

2015

A multiscale approach, based on the combination of CALPHAD and molecular dynamics (MD) simulation, is applied in order to understand the melting transition taking place in CuPt nanoalloys. We found that in systems containing up to 1000 atoms, the morphology adopted by the nanoparticles causes the icosahedral CuPt to melt at temperatures 100 K below that of the other morphologies, if the chemical composition contains less than 30% of Pt. We show that the solid-to-liquid transition in CuPt nanoparticles of a radius equal to or greater than 3 nm could be studied using classical tools.

“…The temperature dependent chemical order (or ''compositional structure''), namely, the equilibrium atomic distribution of the two elements among the different surface and core sites of the NP, affects considerably its physical and chemical properties. 10 Recently, atomic site-specific chemical order in fcc-based 201-and 586-atom Pt-Ir truncated-octahedron (TO) nanoparticles was studied 11 by us using near-surface coordinationdependent bond-energy variations (CBEV) 12 as input to the statistical-mechanical free-energy concentration expansion method (FCEM), 13 which takes into account analytically short-range order. Thus, in Cu, Ni or Co alloyed with Ag, the formation of side-separated ''Quasi-Janus'' configurations was attributed to the near-surface elastic strain release using the Gupta potential and computational global optimization.…”

Section: Introductionmentioning

confidence: 99%

Thermally-induced chemical-order transitions in medium–large alloy nanoparticles predicted using a coarse-grained layer model

Polak

Rubinovich

2015

A new coarse-grained layer model (CGLM) for efficient computation of axially symmetric elemental equilibrium configurations in alloy nanoparticles (NPs) is introduced and applied to chemical-order transitions in Pt-Ir truncated octahedra (TOs) comprising up to tens of thousands of atoms. The model is based on adaptation of the free energy concentration expansion method (FCEM) using coordination-dependent bond-energy variations (CBEV) as input extracted from DFT-computed elemental bulk and surface energies. Thermally induced quite sharp transitions from low-T asymmetric quasi-Janus and quasi ball-and-cup configurations to symmetric multi-shells furnish unparalleled nanophase composite diagrams for 1289-, 2406- and 4033-atom NPs. At even higher temperatures entropic atomic mixing in the multi-shells gradually intensifies, as reflected in broad heat-capacity Schottky humps, which become sharper for much larger TOs (e.g., ∼10 nm, ∼30,000 atoms), due to transformation to solid-solution-like cores.