OPTICAL BAND-GAP, INFRARED-ABSORPTION AND THERMAL-DIFFUSIVITY OF GE-GA-SE GLASSES

The results of our measurements on the variation of optical band gap E -g and thermal diffusivity alpha, with average coordination number Z a re reported and discussed for GexGa5Se95-x semiconducting glass sample s. The samples are prepared by the melt quenching technique at a cooli ng rate of approximately 10(2) K/s. In the variation of E-g with Z of these glasses, a maximum in E-g is observed at Z = 2.73 corresponding to the chemical threshold of the system. Threshold maxima are seen at Z values of 2.42 and 2.67 in the alpha versus Z curves of these glasse s. These features are explained in terms of mechanical stiffening of t he glass network due to threshold percolation of rigidity and a two- t o three-dimensional structural transition, both driven by the average coordination of the atoms in the network. The results confirm the exis tence of effects due to topology and local chemical ordering in these glasses.