Vibrational and Configurational Entropy of Liquids and Glasses

Over several decades there has been controversy about the specific heat absorbed as a glass transforms to a liquid—does this originate from vibrational entropy or configurational entropy? We report direct measurements of the total entropy and vibrational entropy of strong and fragile metallic glasses and the molecular glass GeO₂ in the glass, liquid and crystalline states. Inelastic scattering methods were used to measure the vibrational spectra across the glass transition, and the total entropy assessed with calorimetry. These three materials differ fundamentally in their structure, bonding, and glass-forming ability. The configurational disorder in oxide glasses is predominantly orientational, while metallic glasses are characterized by topological disorder. The excess vibrational entropy of the supercooled liquid over the crystalline phase will be compared for all three glass-formers. [Smith, H. L., et al. Nature Phys. 13, 900-905 (2017).]