A detailed analysis of X-ray diffraction data for GexSb40-xS60 glasses
indicates the existence of a topological phase transition and medium-
range order related not only to the first but also to the pre-first sh
arp diffraction peak. The compositional dependence of the intensity, t
he correlation length and the ratio between the position and the width
of the two peaks are compared. Differences between the two peaks are
revealed and their structural implications are discussed.