Consequences of homogenization of bulk As_xS_100-x glasses on their calorimetric and vibrational behavior

Bulk As_xS_100-x melts/glasses of 1.5 gram batch size in the 15% < x < 40% composition range are synthesized by reacting dry As₂S₃ and S at 700°C in evacuated quartz tubes for several tens of days. Ex-situ FT- Raman scattering of the 1 inch long quenched melt columns were periodically taken till these homogenized. A Q2000 MDSC from TA Instruments is used to examine thermal properties of glasses. The results confirm¹ the enthalpy of relaxation at T_g, △H_nr(x) to reveal a sharp square-well like reversibility window in the 22.5% < x < 28.0% range, and T_g(x) to systematically increase with x. FT- Raman scattering experiments reveal the elusive 537 cm^-1 mode associated with As=S stretch predicted for the quasi-tetrahedral (QT) S=As(S_1/2)₃ local structure¹ to be observed. The scattering strength of the QT mode shows a global maximum near x = 18%. The Fragility index of these homogenized melts are being examined and will be correlated with the reversibility window.

1. P, Chen et al. Phys. Rev. B 78, 224208(2008).