Fragility of network-forming glasses: A universal dependence on the topological connectivity.

The fragilities of over 150 different network-forming glass melts are shown to conform to a common dependence on just one parameter: the connectivity of the weakest network structure present in the associated glass solid. This includes both nonoxide network-forming chalcogenide melts as well as a variety of alkali oxide glasses, and spans a broad range of connectivity, ϕ, from polymeric structures (ϕ=2) to overconstrained random networks with connectivities well in excess of the rigidity threshold (ϕ(C)=2.4). A theoretical framework for the origin of this universal pattern is offered within the context of entropic models of the glass transition.