THE PHYSICAL-PROPERTIES AND THE CHEMICAL-BOND APPROACH FOR SE-GE-AS AMORPHOUS-CHALCOGENIDE GLASSES

There is considered interest among experimenters and theorists in the study of the electrical conductivity sigma in structurally disordered state as a function of various external factors: structure, compositio n, temperature, effect of illumination and the effect of chemical bond ing on the physical behaviour of the investigated amorphous thin films Se0.75Ge0.25-yAsy (y = 0.05, 0.10, 0.15 and 0.20) system. X-ray diffr ation patterns indicate the amorphous structure of thin film samples a nd DTA thermograms showed an decrease of T-g with increase of the As c ontent in the system under test. The dependence of the electrical cond uctivity, measured either in darkness or after exposure to different d urations of light, on temperature and exposure time have been studied. The pronounced glass-forming tendencies of alloys of Se and Ge with A s were discussed topologically in terms of the chemical bonds expected to be present in these materials. Using simple considerations based o n coordination number [m] and bond energies, the average number of nea r neighbors of each type expected to surround atom has been estimated. These average numbers of bonds have been used to estimated the cohesi ve energies (CE) of these glasses assuming simple additivity of bond e nergies. On the other hand in random networks, with high average coord ination (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. C opyright (C) 1996 Published by Elsevier Science Ltd.