Formulation of thermodynamics for the glassy state: Configurational energyas a modest source of energy

Glass is an under-cooled liquid that very slowly relaxes towards the equili brium crystalline state. Its energy balance is ill understood, since it is widely believed that the glassy state cannot be described thermodynamically . However, the classical paradoxes involving the Ehrenfest relations and Pr igogine-Defay ratio can be explained when the effective or fictive temperat ure of the slow modes is taken as an additional system parameter. Having st raightened out the proper picture, it is interesting to reconsider glass fr om a thermodynamic viewpoint. A shard of glass, kept at fixed temperature a nd volume, relaxes towards lower energy. Heat is released, inducing apparen t violations of all basic thermodynamic laws. The most interesting applicat ion is to use glassy or amorphous systems as a source of energy, by extract ing the configurational energy in a process of melting followed by crystall ization. (C) 2001 American Institute of Physics.