Nanoscale phase separation of GeS2 glass

Abstract Molecular structure of GexS100-x glasses in the 30 < x < 34 atomic percentage range is examined by Raman scattering, 119Sn Mössbauer spectroscopy, and temperature-modulated differential scanning calorimetry. The results show that the stoichiometric glass with x = 33.33 (T g = 508°C) is chemically disordered. Raman scattering places mode strengths of corner-sharing Ge(S1/2)4 tetrahedra (A), ethane-like Ge2(S1/2)6 units (B), and the distorted rocksalt Ge(S1/6)6 units (C) at approximately 93.4:3.6:3.0 not normalized for mode cross-sections. Mössbauer spectroscopy places the concentration of these units as A : B : C = 76.2:8.8 :15. The drastic reduction in the slope of the glass transition temperature T g with Ge content x coincides with first appearance of these units once x exceeds 32.50, suggesting that these units are demixed and form separate nanophases to lower the global connectivity of the glass network.