Stiffness transitions inSixSe1−xglasses from Raman scattering and temperature-modulated differential scanning calorimetry

Temperature-modulated differential scanning calorimetry (MDSC) measurements on ${\mathrm{Si}}_x{\mathrm{Se}}_{1-x}$ glasses show glass transitions to be thermally reversing in character in the composition window $0.20<x<\mathrm{}\mathrm{0.27.}\mathrm{}$ Raman scattering shows a trimodal distribution of vibrational modes, identified with corner-sharing (CS), edge-sharing (ES), and Se-chain modes (CM). In the floppy region, $0<x<\mathrm{}0.19,$ these modes are symmetric and are characteristic of a random network. In the transition region, $0.20<x<\mathrm{}0.27,$ the ES and CM split into doublets suggesting appearance of extended range structural correlations. In the percolatively rigid region, $x>\mathrm{}0.27,$ the CS mode in addition to the ES and CM also splits into a doublet indicating growth of substantial medium range structure. The large compositional width $\mathrm{}(0.20<x<\mathrm{}0.27\mathrm{})\mathrm{}$ associated with Raman elastic thresholds coincides with the thermally reversing window from MDSC.