Mean-coordination number dependence of the fragility in Ge–Se–In glass-forming liquids

Differential scanning calorimetry measurements have been performed on elemental Se as well as on GexSe94−xIn6 (x=4, 8, and 11 at%) and on GeySe88−yIn12 (y=5, 7, and 9 at%) chalcogenide glasses. From the cooling rate dependence of the fictive temperature, the apparent activation energies, Δh*, and the fragility indices, m, as defined in the strong–fragile glass-forming liquid concept, are determined. It is found that, in Ge–Se–In system, there is an evolution from strong (m=67) to fragile (m=116) glass-forming liquids. The dependence of ‘m’ on the mean-coordination number, Z, is also obtained. This dependence is rationalized by assuming that, in this glassy alloy system, there is a tendency for the formation of In2Se3 clusters.