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

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 L-10 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. (C) 2019 Elsevier B.V. All rights reserved.