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19, 3796–3800 (2007). 9 Zhang X. , Production of complex chalcogenide glass optics by molding for thermal imaging. J. Non-Cryst. Solids, 326, 327, 519–523 (2003). 10 Thorpe M. , Continuous deformations in random networks. J. NonCryst. Solids, 57, 355–370 (1983). 11 Phillips J. , Topology of covalent non-crystalline solids. I. Short-range order in chalcogenide alloys. J. Non-Cryst. Solids, 34, 153–181 (1979). 12 Micoulaut M. and Phillips J. , Rings and rigidity transitions in network glasses.

4. These properties range from density and thermal expansion to glass-forming ability [11, 16, 44]. For example, Fig. 2 shows the density and liquid thermal expansion versus for the binary Ge–Se and ternary Ge–Sb–Se systems. 4. 2 (a) Density as a function of for the binary Ge–Se (squares) and the ternary Ge–Sb–Se (triangles) (adapted from [44]). (b) Liquid-state thermal expansion coefϐicient αL as a function of for the binary Ge–Se (squares) and the ternary Ge–Sb–Se (triangles) (adapted from [16]).

Both sets of data were obtained using EH and Tg values measured by DSC. The trends for both systems show a clear minimum in fragility at the rigidity percolation threshold. 7 Dependence of the fragility index, m, on the average coordination for Ge–Se and Ge–As–Se glasses. The fragility index was derived from the activation energy for enthalpy relaxation measured by DSC using Moynihan’s method. The same trends can be observed using other measures of fragility, including ΔCp and ΔTg/Tg. Note that ΔCp can be used 31 32 Relaxation and Fragility in Chalcogenide Network Glasses without normalization for the purpose of observing trends within a given system.