Fragility, slow homogenization and Intermediate Phase in the Si$_x$Ge$_x$Te$_{100-2x}$ ternary

Small sized (0.5g) melts were synthesized by reacting pure elements in 5mm ID quartz tubes at 950C, and examined after 1 week and then 2 weeks of reaction. Bulk glass formation is realized in 6{\%}\textless x\textless16{\%} range with Tg(x) increasing linearly in 6{\%}\textless x\textless12{\%} range, and decreasing thereafter (x\textgreater12{\%}). The enthalpy of relaxation at Tg shows a flat bottomed minimum in 7.5{\%}\textless x\textless9.0{\%} range with the term increasing sharply at x\textgreater9{\%} and at x\textless7.5{\%}. We identify the 7.5{\%}\textless x\textless9.0{\%} range with the Intermediate Phase. Fragility(m) of melts were established in complex Cp measurements, and show a global minimum (m\textless30) in the IP range, and a value of m=26 at x=8.5{\%}. The slow homogenization of Telluride melts results from the \textit{strong} character of IP melts. Raman scattering, excited using low power density of 785nm radiation, shows evidence of a broad mode near 160cm$^{-1}$ (characteristic of a-Te chains) and a narrower one near 127cm$^{-1}$ (group IV crosslinking units). The scattering strength of the 127cm$^{-1}$ mode increases at the expense of the 160cm$^{-1}$ mode as x increases. The nature of structure evolution with glass composition will be commented upon.