Vibrational entropy near glass transition in a chalcogenide glass and supercooled liquid

Raman spectroscopic measurements have been performed on Ge20Se80 glass and supercooled liquid at temperatures ranging between 298 and 500 K. Temperature dependent softening of vibrational mode frequencies has been used in conjunction with the available vibrational density of states data at ambient temperature to estimate the relative contributions of vibrational and configurational entropies across glass transition. Nearly 20% of the additional entropy above glass transition is estimated to be vibrational. Thermal expansion effect on vibrational mode softening is found to be insufficient to account for the anharmonic component of vibrational entropy implying possible coupling between the vibrational and configurational entropies at temperatures above Tg. These results may have important consequences in shaping our understanding of various aspects of glass transition.