MADELUNG POTENTIALS IN DISORDERED-SYSTEMS

We analyse the contribution of Madelung terms to the local potential o n atomic sites in disordered alloys, and assess the extent to which th e variation in the local potential should be observable in high-resolu tion x-ray photoelectron experiments. We show that a model in which th e charge on an atom is determined by the global composition predicts c onsiderable broadening of core-level photoelectron spectra. Such disor der broadening has not been observed experimentally. A model in which the local charge is determined by the number of 'unlike' nearest neigh bours predicts a much smaller disorder broadening, but one which shoul d be observable in high-resolution measurements for some alloy systems .