Residual entropy and structural disorder in glass: Fluctuation phenomena and time-dependent features as deduced from an Ising-type structural model

As part of our study of configurational entropy in non-equilibrium systems, we have determined the time-dependent fluctuations in a simple system that undergoes structural transformations similar to those of an Ising model. First, we demonstrate that the calorimetric entropy does approximate the statistical thermodynamic entropy, and that the former reflects the spatial arrangements dealt with by the latter. We then show that neither the assumption of ergodicity nor the use of a canonical ensemble is required to account for non-equilibrium states. We use instead the concept of ‘spatial sampling’ with which enthalpy, entropy and volume can be defined for each structure at any time. In this way fluctuations of all variables can be calculated without any inconsistency. Finally, we point out that introduction of the new concepts of magnitude and phase factor into configurational entropy can not only explain the existence of residual entropy at 0 K for disordered materials but also allows one to discuss spatially related randomness and kinetically induced fluctuations on an equal footing.