Differential scanning calorimetry measurements have been performed on elemental Se as well as on GexSe94ÀxIn6 (x ¼ 4, 8, and 11 at%) and on GeySe88ÀyIn12 (y ¼ 5, 7, and 9 at%) chalcogenide glasses. From the cooling rate dependence of the fictive temperature,the apparent activation energies, Dh*, 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 ¼ 67) to fragile (m ¼ 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.

r 2006 Elsevier B.V. All rights reserved