Multiscale approach for studying melting transitions in CuPt nanoparticles

Abstract

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.

Thermodynamics of CuPt nanoalloys

“…5 right panel, we identify an onion-shell elemental distribution, both according to itMD and NS calculations: the outermost shell contains two thirds of the total copper population; the subsurface is Pt-rich (hitting the ); the third and fourth layers have a 60% of Cu and 40% Pt, respectively. This onion-shell chemical ordering is preserved above the melting point and high temperature NS configurations show that it is the most favourable up to 2500 K, supporting the idea that it should be considered as the equilibrium chemical arrangement, in agreement with previous in-silico 32 , 63 and in-vitro 48 studies. It is interesting to note that in correspondence of the melting transition the radial distribution function identifies an atom at the center of the cluster, while earlier the center of mass of the system felt in between atoms.…”

“…Metal-metal interactions are modelled following the second moment approximation of the tight binding theory, in the Rosato-Guillope’-Legrande formulation 50 , and their parametrisation is taken from ref. 32 . The choice of a tight binding potential in second-moment approximation (TB-SMA) to describe interatomic interactions is dictated by the long time and length scales involved in our calculations.…”

Pt–Co nanocluster in hollow carbon nanospheres

“…To investigate the chemical ordering in the nanoclusters, we have mapped the radial chemical distribution function (RCDF) for the 309 atoms clusters in Figure . Going from the center of mass of nanocluster outwards, the molar ratio of Pt and Co was monitored within the volume delimited by two spherical surfaces, with radii r RCDF and r RCDF + ɛ , respectively ( ɛ is the thickness and was fixed at 0.3 Å) . The white spaces which can be seen in Figure are the regions where no atom exists within a particular radial segment (due to the ordered structure of the solid state).…”

“…Therefore, the mixed structure is the most stable structure of the bare and encapsulated Pt/Co nanoclusters. To investigate the chemical ordering in the nanoclusters, we have mapped the radial chemical distribution function (RCDF) [69,70] for the 309 atoms clusters in Figure 6. Going from the center of mass of nanocluster outwards, the molar ratio of Pt and Co was monitored within the volume delimited by two spherical surfaces, with radii r RCDF and r RCDF 1 E, respectively (E is the thickness and was fixed at 0.3 Å ).…”

“…Going from the center of mass of nanocluster outwards, the molar ratio of Pt and Co was monitored within the volume delimited by two spherical surfaces, with radii r RCDF and r RCDF 1 E, respectively (E is the thickness and was fixed at 0.3 Å ). [69,70] The white spaces which can be seen in Figure 6 are the regions where no atom exists within a particular radial segment (due to the ordered structure of the solid state). As the cluster is heated, the number of the white spaces decreases which is due to the increasing the structural disorder in the nanocluster.…”