Short, intermediate and mesoscopic range order in sulfur-rich binary glasses

Pulsed neutron and high-energy X-ray diffraction, small-angle neutron scattering, Raman spectroscopy and DSC were used to study structural changes on the short, intermediate and mesoscopic range scale for sulfur-rich AsSx (x >= 1.5) and GeSx (x >= 2) glasses. Two structural regions were found in the both systems. (1) Between stoichiometric (As2S3 and GeS2) and 'saturated' (AsS2.3 and GeS2.7) compositions, excessive sulfur atoms form sulfur dimers and/or short chains, replacing bridging sulfur in corner-sharing AsS3/2 and GeS4/2 units. (2) Above the `saturated' compositions at [As] < 30.5 at.% and [Ge] < 27 at.%, sulfur rings and longer sulfur chains (especially in the AsSx system) appear in the glass network. The glasses become phase separated with the domains of 20-50 (A) over circle, presumably enriched with sulfur rings. The longer chains S are not stable and crystallize to c-SS on ageing of a few days to several months, depending on composition. (c) 2005 Elsevier B.V. All rights reserved.