Property Extrema In Geas Sulphide Glasses

GeAsS glasses with Ge:As ratios of 2.5:1, 1:1 and 1:2 with S concentrations ranging from 35-80%, corresponding to an average coordination number ((r)) ranging from 2.35 to 2.98 were synthesized. For glasses with fixed Ge:As ratio, the absorption edge and the glass transition temperature vary monotonically with S content. The thermal expansion coefficient and molar volume, however, attain maxima at (r) near 2.6, which extrema correspond to a maximum in the relative intensity of a narrow polarized Raman band at 275n cm-1 and a minimum in the frequency of the boson peak.