RIGIDITY PERCOLATION AND CHEMICAL ORDERING IN GE-IN-SE GLASSES

The dependence of the mean atomic volume V-a of chalcogenide glasses b elonging to the GexIn6Se94-x and GexIn12Se88-x families of the Ge-In-S e system, on the average coordination number Z is investigated. The V- a-Z plots for both families display maxima at Z = 2.75 and 2.83 corres ponding to the tie-line composition in In-6 and In-12 families, respec tively. The V-a-Z dependence for the In-6 family exhibits a minimum at Z = 2.54 and a broad local maximum at Z = 2.67, and that of the In-12 family shows a marked change in slope at Z = 2.50. These results are discussed in the framework of the chemically ordered covalent network model, Tanaka's model of topological transition, and the Phillips-Thor pe model of rigidity percolation.