Raman signatures of intermediate phase in quaternary Ge15Te80 − xIn5Agx glasses

In thermally annealed samples, a unique variation of Raman wave-numbers in the intermediate region is observed due to the retention of some of the local structure even after the sample is crystallized. The observed Raman peaks are attributed to crystalline tellurium and silver lattice vibrational modes. Based on our present and earlier studies, we propose the occurrence of three thresholds in Ge15Te80 − xIn5Agx glasses, namely percolation of rigidity, percolation of stress and the onset of chemical phase separation on a nanoscale at 8%, 16% and 20% of silver concentration respectively.