The mechanism of chemical disordering in Cu_3An nanometre-sized systems

摘要

Classical molecular dynamics simulations have been employed to investigate the order-disorder transformation in Cu_3AU 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. (Some figures in this article are in colour only in the electronic version)