Nanoscale phase separation of GeS2 glass

Molecular structure of GexS100-x glasses in the 30 < x < 34 atomic percentage range is examined by Raman scattering, Sn-119 Mossbauer spectroscopy, and temperature-modulated differential scanning calorimetry. The results show that the stoichiometric glass with x = 33.33 (T-g = 508degreesC) is chemically disordered. Raman scattering places mode strengths of corner-sharing Ge(S-1/2)(4) tetrahedra (A), ethane-like Ge-2(S-1/2)(6) units (B), and the distorted rocksalt Ge(S-1/6)(6) units (C) at approximately 93.4 : 3.6 : 3.0 not normalized for mode cross-sections. Mossbauer 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.