Raman signatures of intermediate phase in quaternary Ge15Te80−xIn5Agx glasses

Abstract Micro-Raman studies are conducted on as-quenched and annealed Ge 15 Te 80 − x In 5 Ag x glasses to probe the structural network and its evolution with composition. These studies reveal the presence of tetrahedral GeTe 4 structural units in as-quenched samples. Specific signatures of the intermediate phase (IP) are observed in the composition dependence of Raman frequencies and corresponding intensities of different modes in the composition range, 8 ≤ x ≤ 16. In addition, the Raman peak positions are found to shift with silver doping. Apart from the Raman results, the compositional dependence of density, molar volume and thermal diffusivity, observed in the present study, confirms the presence of the intermediate phase. 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 Ge 15 Te 80 − x In 5 Ag x 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.