Physical properties and Raman spectroscopy of GeAs sulphide glasses

Ternary GeAsS glasses have been investigated to determine the compositional dependence of selected physical properties. Although the latter show a linear variation with Ge:As ratio at a constant S content, many exhibit a non-linear dependence on the S content at a fixed Ge:As ratio. The trend of optical properties tracks the increasing formation of metal–metal bonds as the S concentration of these glasses is reduced below stoichiometry. Molar volume and thermal expansion coefficient display maxima near an average coordination number of 2.6 for which there is no apparent indication in the Raman spectra. The spectra of stoichiometric and S-excess glasses are dominated by a band at 345 cm−1 due to the symmetric stretching of both AsS3 and GeS4 groups; those of S-deficient glasses display bands associated with metal–metal bonds between 210 and 240 cm−1 whose intensity increase with increasing S deficiency.