The mechanism of chemical disordering in Cu3Au nanometre-sized systems

Classical molecular dynamics simulations have been employed to investigate the order-disorder transformation in Cu3Au unsupported particles in the mesoscale regime between 1 and 10 nm. The reliability of the many-body potential employed was tested by means of ab initio computations. Temperature and observed latent heat of transition are remarkably depressed when compared with those of a surface-free bulk. The detailed study of the thermal behaviour of a 4 nm particle reveals that the disordering process has a heterogeneous character. It starts at the surface, where vacancies and atoms with defective coordination appear at relatively low temperatures. Au segregation phenomena take place contemporarily, establishing a concentration gradient between particle surface and bulk. The latter progressively disorders at increasing temperature due to the proliferation of atoms with defective coordination.