Thermodynamic Analysis of the Pt-Au Miscibility Gap.

The thermodynamic properties of Pt-Au alloys were determined by an analysis of the miscibility gap. The method applied is based on the idea that two effects are responsible for the deviations from the ideal behavior, namely that gold donates its valence electron to the electron gas of the alloy raising its Fermi energy and that there exists an energy of attraction between the solute gold atoms brought about by lattice distortion. The dominating influence of the pair interaction on thermodynamic properties is responsible for the high critical temperature of the miscibility gap. The asymmetrical shape of the miscibility loop is attributed to the Fermi energy rise upon filling unoccupied 5d and 6s states of the alloys.