Analysis of Au-Pd driving forces via the effective site energy model: LRO, antisites and enthalpy of permutation

Recently we have developed a new energetic model based on the determination of the energies on each site of random solid solutions after relaxation as a function of both the local composition and the nominal concentration. It allows to determine the main thermodynamics driving forces of disordered alloys. Here, we extend the effective site energy model to ordered alloys and illustrate the results for the Au_cPd_1-csystem. As a first step, we show the ability of this energetic model to reproduce the hierarchy of ordered phases. Then, we derive general mean-field analytic formulae for ordered systems and get the phase diagram. We determine the relative role of the cohesive effect, the chemical effect and the size effect and find that the chemical effect differs significantly between the disordered state and the ordered state. Finally, we link the energy formation of antisite to the permutation enthalpy and give the driving forces for the formation of antisite.