Abstract
The pair-bond approximation and the mean-field approach are used to derive an expression for the free energy of surface segregation in binary alloys. It is suggested that a correction term, in addition to the surface energy term and the heat of solution, should be included in the free energy of segregation in order to obtain a better quantitative agreement between theory and experiment. This correction term is a concentration-dependent quantity and therefore cannot be obtained from pure-metal properties. The theory is applied to Cu-Ni alloy, and if the correction term is properly chosen, then a good quantitative agreement with experiment is found for all in-depth surface compositions. The free energy of segregation obtained by this method is in qualitative agreement with that calculated on surface core-level shifts. This is not the case if the correction term is not considered.
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