Role of intermediate-range order in predicting the fragility of network-forming liquids near the rigidity transition

Studies of network-forming oxide liquids are combined with studies of network-forming chalcogenide glasses to demonstrate a universal dependence of the glass forming fragility on the topological connectivity of the network. This connection between structure and dynamics is congruent with theoretical predictions for a rigidity transition near an average bond number of 2.4, and the common pattern of fragility may be traced via a simple two-state bond model to a common variation of configurational entropy with connectivity. However, in order for this universality to appear the connectivity of the oxide networks must be defined in a progressive manner that accommodates the presence of those rigid structural units that comprise both the short-range and intermediate-range order. Replacement of these robust structural units by equivalent network nodes is necessary but can be viewed as a coarse-graining of the network to a bond lattice of weakest links that are most relevant to zero-frequency properties like the fragility.