Variation in fragility-index, Enthalpy of relaxation at T_g and Molar volumes in especially homogenized bulk As_xS_100-x glasses

We have measured the variation of fragility index (m), Non-reversing enthalpy of relaxation (ΔH_nr) and molar volumes (V_m) with x in especially homogenized As_xS_100-x batches of 1.5 gram in size. FT Raman profiling was used to ascertain homogeneity of glasses. Our results show that ΔH_nr displays a square-well like minimum in the 22.5(5)% < x < 28.5(5)% range defining the reversibility window¹. Variation of m displays a minimum of m < 20 in the same range of x, defining the fragility window. Inverse of the activation energy (E_a) for enthalpy relaxation shows a maximum in the IP. Variation in V_m(x) displays a Gaussian-like local minimum in the reversibility window. The fragility-window coinciding with the reversibility window underscores that super-strong (fragile) melts upon cooling give rise to IP (non-IP) glasses. The maximum in 1/E_a shows that the excess configurational entropy² of melts (S_ex) peaks for IP glasses, On the other hand, the large build up in ΔH_nr and small increase in ΔC_p for non-IP compositions (as x > 28.5(5)% and x < 22.5(5)%) as one goes away from the IP, accounts for the increased fragility of stressed-rigid and flexible melts.

1. Chen, P. et al. Phys. Rev. B 78, (2008)
2. Sidebottom, D.L. Phys. Rev. E 92, (2015)