Anomalous X-ray scattering study of the local structure in Ge-Se glasses

Anomalous X-ray scattering experiments on glassy Ge_xSe_1−x semiconductors have been carried out at energies close to the Ge and Se K edges in a wide concentration range from x = 0.15 to 0.333 across the rigidity percolation threshold composition of x = 0.20. The total structure factors, S(Q), show considerable variation with x in both the position and intensity of the prepeak at about 10 nm⁻¹, while in the remaining Q range, it stays almost unchanged. The differential structure factors, Δ_iS(Q), comprise characteristic features, depending on the absorption edges. Comparing them suggests that the prepeak indicating the existence of intermediate-range order (IRO) purely originates from the Ge-Ge partial correlations. In contrast to the S(Q), the prepeak in Δ_GeS(Q) changes very slightly with varying x down to x ∼ 0.20, suggesting that the prepeak height in S_GeGe(Q) largely enhances with decrease in the Ge concentration, in particular at the the rigidity percolation threshold composition. However, a sudden decrease and a shift of the Q position are seen at the Ge concentration less than the stiffness transition composition, which may relate to the sudden decrease of the GeSe₄–GeSe₄ connections in the floppy region of this glassy system.