Chemical ordering and surface segregation in Ni1-cPtc system: A theoretical study from the alloys to the nanoalloys

Abstract

Monte Carlo simulations within a Tight-Binding Ising Model (TBIM) have been performed on bulk, surfaces, and nanoclusters of Ni1-cPtc alloys in order to describe and understand the competition between surface segregation and chemical ordering phenomena in nanoalloys. The effective pair interactions obtained from the DFT calculations have been applied in Monte Carlo simulations to determine the bulk and alloy surfaces configurations. The order-disorder transition temperatures in the bulk compare well with experimental data and the bulk phase diagram from the model have been compared to that determined experimentally to validate the fit. The (111), (100) and (110) crystallographic orientations surfaces Ni1-cPtc are treated. The three driving forces for the segregation of surfaces have be studied in both diluted limits, together with the phenomenon of segregation at high temperature (in the disordered state) over the entire concentration range. Finally, we analyze the competition between superficial segregation and low temperature chemical order and conclude with a similar approach on truncated octahedra of 1289 and 405 atoms. Keywords: Tight-Binding Ising Model, Alloys surfaces, Nanoalloys, Segregation, Order-disorder transition