Temperature Dependence of the SeH Vibrational Dephasing Time in Chalcogenide Glasses
The concept of relating the properties of glass-like solids to their microscopic topology rather than to their chemical nature was originally introduced by Phillips  and later refined by Thorpe. The key parameter in this model is the mean coordination number <r>, i. e. the average number of covalent bonds per atom. Constraint counting arguments lead to topological thresholds at <r> = 2.4 and <r> = 2.67. Both can be observed in different glasses as extrema or kinks in physical properties as a function of the mean coordination number, such as the glass forming temperature, the mean atomic volume or the dielectric constant[3–5].