Elastic transition thresholds in Ge-As(Sb)-Se glasses

We prepared several groups of Ge_xAs_ySe _1-x-y and Ge_x Sb_y Se_1-x-y glasses with a fixed y at 10 at%, 15 at% and 20 at%, respectively, and measured their density and elastic moduli with the aim of understanding the correlation between the chemical compositions, the mean coordination numbers (MCNs) and the physical properties. It was found that whilst the glass density on average showed a maximum around MCN≈2.45 and a minimum at MCN≈2.6, varying the proportion of the chemical elements could modify the density and smear out these transition thresholds. The elastic moduli of the glasses were estimated from the shear and compressional wave velocities measured by ultrasonic pulse interferometry. We simultaneously observed two elastic transition thresholds: the first one at MCN≈2.45 and the second one at MCN≈2.6, which appear to be closely correlated with changes in the glass microstructure. However, differences were observed in the elastic moduli of groups of samples with the same MCN = 2.4 and 2.6 but different compositions suggesting that the chemical compositions also influence the elastic properties especially in the Ge-Sb-Se glasses where the elements have larger differences in mass and atomic radius.