Thermodynamics and kinetics of ordered and disordered Cu/Au alloys from first principles calculations

Abstract

First principles calculations are used to elucidate the thermodynamic stability of Cu–Au alloys. Here, we particularly focus on the Au-rich compositions which lie extremely close to the convex-hull. We find that there are multiple metastable states that are superstructures of the layered L10 Cu0.5Au0.5 ground state. We also examine the effect of epitaxy on the ordered ground states of Cu–Au phases when the underlying substrate is Au. We find that the Au-rich phases remain stable, depending on the growth planes, while the Cu-rich phases are destabilized. We relate these results to the dealloying and nucleation of Au-rich phases observed experimentally. We perform Nudged Elastic Band calculations in both ordered and disordered Cu–Au phases to determine the activation energies of diffusion. The ordered phases show unique minimum energy paths due to uniform local environments of the species, while the disordered phases show a distribution of transition states, governed by the local density and the local bonding environments of diffusing species.