Coexistence of topological and chemical ordering effects in Ge-Ga-Se glasses

Results of measurement of the mean atomic volume, V and the glass transition temperature, Tg, on 32 glass compositions, belonging to the GexGa5SE95-x, GexGa10Se90-x and GexGa15Se85-x families of the Ge-Ga-Se system are reported and discussed. In the dependence of V and of Tg on the average coordination number, Z, features are seen at values of Z approximately 2.40 and 2.67, which are due, respectively, to the floppy to rigid transition and the structural transition occurring in network glasses. Further, due to the coexistence of the effects which have topological origin and the effects which have their origin in chemical ordering, additional features are seen at the chemical thresholds of the various families of the system. Consolidation of the data on V as a function of Z of several chalcogenide glass systems has indicated the necessity of retaining the chemical identity of the various compositions even when the variation of a property with Z is being considered. Grouping of compositions belonging to specific families of the various systems, rather than considering the data of a system in totality or at random, helps in deciphering effects which are otherwise poorly resolved in several systems