Electronic components in the thermodynamic excess potentials of noble metals alloys

Abstract

Measurements of the chemical excess potentials and their dependence on concentration are characterized by a flat slope at dilute concentrations becoming increasingly steeper as the concentration rises. In order to analyze this behavior the different possible contributions to the excess potentials have been checked. For alloys of copper and silver with impurity atoms of higher valence having the same ion core as the matrix particularly the electronic interaction seems to play the dominant role. This electronic contribution is calculated for a rigid band model of the Jones type and a modification given by Friedel. The former can be shown to be inapplicable to these alloys, whereas the latter indicates at least the right trends, particularly for the slope at infinite dilution. It is thus shown, that it is not possible to draw conclusions concerning the electronic density of states of the pure matrix from the initial slope of the plots of chemical excess potentials versus concentration as proposed by other workers. The experimentally determined initial slope comes very close to the predictions of the Friedel approach.