Formulation of thermodynamics for the glassy state: configurational energy as a modest source of energy

Glass is an under-cooled liquid that very slowly relaxes towards the equilibrium 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 Prigogine-Defay ratio can be explained when the `effective' or `fictive' temperature of the slow modes is taken as additional system parameter. Having straigtened out the proper picture, it is interesting to reconsider glass from a thermodynamic viewpoint. A shard of glass, kept at fixed temperature and volume, relaxes towards lower energy. Heat is released, inducing apparent violations of all basic thermodynamic laws. The most interesting application is to use glassy or amorphous systems as a source of energy, by extracting the configurational energy in a process of melting followed by crystallization.