| Abstract: | Metallic alloy clusters at equilibrium display an inhomogeneous stress field which may
contribute to the chemical ordering and segregation properties. We use the example of
cuboctahedral and icosahedral Au-Pd clusters with the same size to compare these
properties in systems displaying moderately and highly inhomogeneous stress fields.
Metropolis Monte Carlo simulations in the semi-grand canonical ensemble are used with an
empirical potential to predict equilibrium configurations. Pressure maps are used to
estimate stress on each atom. It is found that when the stress field is moderately
inhomogeneous, ordering is dominantly driven by thermodynamic forces. In icosahedral
clusters, ordering is found to be the consequence of a balance where thermodynamic forces
and mechanical stress may conflict or reinforce each other. Order-disorder transitions are
smoother in the systems with higher stress inhomogeneity and it is conjectured that, in
icosahedral clusters, disorder may nucleate in the central core. |
