Insights into glass formation and glass transition in supercooled liquids, by study of related phenomena in crystals

C. Austen Angell

Published 2007-12-27Version 1

We divide glass and viscous liquid sciences into two major research areas, the first dealing with how to avoid crystals and so access the viscous liquid state, and the second dealing with how liquids behave when no crystals form. We review some current efforts to elucidate each area, looking at strategies for vitrification of monatomic metals in the first, and the origin of the property fragility in the second. Essential here is the non- trivial behavior of the glassformer thermodynamics. We explore the findings on nonexponential relaxationand dynamic heterogeneities in viscous liquids, emphasizing the way in which direct excitation of the configurational modes has helped differentiate configurational from nonconfigurational contributions to the excess heat capacity. We then propose a scheme for understanding the relation between inorganic network and non-network glassformers which includes the anomalous case of water as an intermediate. In a final section we examine the additional insights to be gained by study of the ergodicity-breaking, glass-like, transitions that occur in disordering crystals. Here we highlight systems in which the background thermodynamics is understood because the ergodic behavior is a lambda transition. Water and the classical network glassformers appear to be attenuated versions of these.