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 AsS_x (x ? 1.5) and GeS_x (x ? 2) glasses. Two structural regions were found in the both systems. (1) Between stoichiometric (As₂S₃ and GeS₂) and ‘saturated’ (AsS_2.3 and GeS_2.7) compositions, excessive sulfur atoms form sulfur dimers and/or short chains, replacing bridging sulfur in corner-sharing AsS_3/2 and GeS_4/2 units. (2) Above the ‘saturated’ compositions at As] < 30.5 at.% and Ge] < 27 at.%, sulfur rings and longer sulfur chains (especially in the AsS_x 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 S_n are not stable and crystallize to c-S₈ on ageing of a few days to several months, depending on composition.