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 Å, presumably enriched with sulfur rings. The longer chains Sn are not stable and crystallize to c-S8 on ageing of a few days to several months, depending on composition.