The physical properties and the chemical bond approach for Se-Ge-As amorphous chalcogenide glasses

Abstract

There is considered interest among experimenters and theorists in the study of the electrical conductivity σ in structurally disordered state as a function of various external factors: structure, composition, temperature, effect of illumination and the effect of chemical bonding on the physical behaviour of the investigated amorphous thin films Se 0.75 Ge 0.25 − y As y ( y = 0.05, 0.10, 0.15 and 0.20) system. X-ray diffration patterns indicate the amorphous structure of thin film samples and DTA thermograms showed an decrease of T g with increase of the As content in the system under test. The dependence of the electrical conductivity, measured either in darkness or after exposure to different durations of light, on temperature and exposure time have been studied. The pronounced glass-forming tendencies of alloys of Se and Ge with As were discussed topologically in terms of the chemical bonds expected to be present in these materials. Using simple considerations based on coordination number 〈 m〉 and bond energies, the average number of near neighbors of each type expected to surround atom has been estimated. These average numbers of bonds have been used to estimated the cohesive energies (CE) of these glasses assuming simple additivity of bond energies. On the other hand in random networks, with high average coordination (amorphous solids) the rigid regions have percolated to form a rigid solid with a few floppy or spongy inclusions. A trial was made to correlate our results with available published experimental data.