Intermediate-range order in glassy Ge Se1− around the stiffness transition composition

X-ray scattering measurements on glassy GexSe1−x were performed in a concentration range x=0.07–0.333 in fine steps of 0.005–0.05, in order to explore the relation between the intermediate-range order (IRO) and the stiffness transition in this glassy system. The oscillations beyond the first peak around 20.5 nm−1 in the structure factor, S(Q), remain almost unchanged or damp very slowly with decreasing the Ge concentration x, suggesting the preserve of the short-range order. On the other hand, the pre-peak around 10–12 nm−1, indicating the existence of IRO, systematically changes with decreasing x; its Q position shifts towards the higher Q values and its area decreases. Especially near the onset of the stiffness transition, x=0.20, the peak position starts to deviate from the linear relation. The origin of the pre-peak is discussed in connection with results of a recent anomalous X-ray scattering measurement indicating two contributions of Ge–Ge and Se–Se correlations. Around the onset composition of the stiffness transition, the area of the pre-peak associated with the Ge–Ge correlation has a plateau-like gradual decrease with x followed by a rapid decrease at x<0.18, which is in good agreement with Raman data.