CALPHAD modeling of the glass transition for a pure substance, coupling thermodynamics and relaxation kinetics

On Structural Rearrangements Near the Glass Transition Temperature in Amorphous Silica

“…The configurational entropy of a material is determined by the number of configurons Nc that are accessible to it at the given temperature T, as follows [ 76 ]: S c = k B lnW = k B ln[N c (T)] where k B is the Boltzmann constant, W is the total number of distinct packing states that are available to a system, and W = N c (T) while T < T g . This term exists at any finite temperature T > 0 and cannot be arbitrarily set to zero as is most often done in the two-level models, such as that described in [ 63 ]. However, above T g , a new term needs to be added to the configurational entropy of liquid (Equation (16)), which is due to the formation of the percolation cluster that is made up of configurons, where atoms exploit their new degree of freedoms as more space becomes available for the cluster’s motion: S pc = k B ln[N p (T)] …”

“…Based on Frenkel’s [ 58 ] and Trachenko et al’s [ 59 , 60 , 61 , 62 ] works, we conclude that when additional availability for atomic motions is ensured, the material shifts from solid-like to gas-like type behavior. In line with Benigni’s statement on liquid-like (the B phase in the two-state model) [ 63 ], the state of atoms, which are included in the percolation cluster made up of configurons, is assimilated into a gas-like type with consequent contributions to the heat capacity of material and its mechanical properties. Thus, the glass–liquid transition temperature can be found from the condition of reaching the percolation threshold f c [ 29 , 44 , 45 ]: f(T g ) = f c …”

On Structural Rearrangements during the Vitrification of Molten Copper

“…Additional availability for atomic motions is ensured and the material shifts from the solid-like to the gas-like type behaviour [24][25][26][27][28]. The Benigni's liquid-like B phase in the 2-state model [29] is formed and the state of atoms within the percolation cluster made up of configurons is assimilated to a gas-like type with consequent contributions to the heat capacity of material and its mechanical properties [16,29].…”

The Modified Random Network (MRN) Model within the Configuron Percolation Theory (CPT) of Glass Transition

“…In our case, we applied the set theory to the set of chemical bonds which can be either intact or broken due to thermal fluctuations. In such a way, we are dealing with a typical two-level system that is well developed theoretically as a tool to describe amorphous materials and the glass transition [40,41]. Focusing on just broken bonds termed configurons reveals that at absolute zero T = 0, there are no broken bonds in the glass, whereas at finite temperatures, broken bonds are formed by thermal fluctuations.…”