Physical properties of GexAs2xTe100 − 3x glasses and Raman spectroscopic analysis of their short-range structure

Ternary GexAs2xTe100 − 3x glasses with 20 ≤ 3x ≤ 70 have been investigated to determine the compositional dependence of select physical properties. Molar volume, viscosity, optical band gap and thermophysical properties display a monotonic and often linear variation with the Te content in these glasses. Such compositional dependence is hypothesized to be due to the progressive replacement of a three-dimensional network of corner-shared Ge and As centered coordination polyhedra by –Te–Te–Te– chains as the Te content increases. This topologic change arises as Ge/As–Ge/As bonds in Te-deficient glasses are gradually replaced by Ge/As–Te bonds and ultimately the Te–Te bonds in Te-excess glasses. The compositional evolution of the Raman spectra of these glasses is shown to be consistent with this structural scenario. Furthermore, detailed analysis of the Raman spectra shows significant violation of chemical order in the form of the presence of Te–Te (Ge/As–Ge/As) bonds in Te-deficient (-excess) glasses. Such behavior in ternary Ge–As telluride glasses is unique in comparison with their sulfide and selenide counterparts.