Ordering and surface segregation inCo1−cPtcnanoparticles: A theoretical study from surface alloys to nanoalloys

Abstract

Monte Carlo simulations within a tight-binding Ising model (TBIM) have been performed on bulk, surfaces, and nanoclusters of Co 1-c -Pt c alloys in order to describe and understand the competition or synergy between surface segregation and chemical ordering phenomena in nanoalloys. Considering effective pair interactions (EPIs) up to the third neighbors, we put in evidence new ordered phases at low temperature in the Co-Pt bulk phase diagram. On the infinite ( 100) and ( 111) surfaces, the Pt surface segregation leads to select the Pt-rich plan at the surface without modification of the bulk ordering in the (100) orientation but with an extension of the ordering on a larger composition range in the (111) orientation as compared to the bulk. The truncated octahedron clusters of 405 and 1289 atoms are studied. Their chemical structure is compared in their core with the bulk phase diagram and in their facets with the ( 111) and ( 100) infinite surfaces segregation isotherms. The cluster core presents an asymmetry as compared to the bulk phase diagram. The (111) facets are similar to the (111) surface, whereas the (100) facets present geometrical frustrations for the segregation versus core ordering.

Investigations of the Co-Pt alloy phase diagram with neutron diffuse scattering, inverse cluster variation method, and Monte Carlo simulations

“…In most parametrizations of the tight-binding formalism within the second moment approximation of the electronic density (TB-SMA), the ordering temperature is below the measured one (within a 15%-50% interval) [23][24][25][26] . A recent calibration provides better results since the ordering temperature of the CoPt and CoPt 3 phases were in good agreement with experiments 22 .…”

“…This shows that effective pair interactions determined from diffuse scattering measurements on Co-Pt alloys can be used as quantitative data for developing atomic interaction potentials -implemented on-or off-lattices -capable of describing accurately the main features of the alloy phase diagram (ordering temperatures, asymmetry, compositions related to congruent transformations). This step is the basis for studies devoted to precipitation kinetics 18,19 or surface and interface phase stability [20][21][22] for example.…”

IrPd nanoalloys: simulations, from surface segregation to local electronic properties

“…Both TBIM and Monte Carlo simulations were extensively used to characterize chemical arrangements and surface segregation in alloys (Roussel et al 1997;Saúl et al 1994;Tréglia et al 1999;Gauthier et al 2003). More recently TBIM has been also used to study ordering and segregation in CoPt nanoalloys (Lopez et al 2015). We extend here their utilization to IrPd nanoalloys.…”

First principles study of bimetallic Ni13−nAgn nano-clusters (n = 0–13): Structural, mixing, electronic, and magnetic properties

“…Here E(Ni m Ag n ) is the energy for the MES of the binary Ni m Ag n cluster, while E(Ni 13 ) and E(Ag 13 ) are the energies of MESs of the pure Ni 13 and Ag 13 clusters respectively. It gives a measure of the energy gain for the binary cluster with respect to the segregated phase consisting of two independent clusters of m 13 × N i 13 and n 13 × Ag 13 .…”

“…[1][2][3][4][5][6] During the last few decades, bimetallic nano-clusters have received special interest in the research of nano science and nano technology because of the additional degrees of freedom achievable by changing the chemical composition and ordering of its constituent atoms. Recently, several bimetallic multifunctional nano systems consisting of magnetic transition metal (M) and nonmagnetic noble metal (NM) atoms such as Fe-Pt, [7] Fe-Pd, [8] Fe-Au, [9,10] Fe-Ag, [11] CoPt, [12,13] Co-Pd, [14] Co-Au, [15] Ni-Pt, [16] Ni-Pd, [17] Ni-Au [18], have been studied both experimentally as well as theoretically. Besides their catalytic properties, the M-NM bimetallic nano-systems have also great importance in the fields of fuel cells, magnetic storage as well as in spintronics applications.…”