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The effect of adding iodine to the binary systems As.Se on the thermal stability of the ternary glasses thus formed was investigated by DTA and DDTA. The investigated glasses corresponded to different regions of the phase diagram, i.e. they had different contents of As and I and, consequently, contained different types of structural units.In the investigated ternary systems with iodine, the crystallization effect appears at a lower temperature than in the binary glass As40Se60, and the same holds for the temperatures of softening and melting.For both binary and ternary systems, the activation energies of crystallization were determined. The glass As40Se~o exhibited a somewhat higher activation energy, i.e. a somewhat lower tendency to crystallize than the ternary system.The critical cooling rates of the melts for minimum degree of crystallinity were estimated. The obtained values are approximately equal for the binary (As2S03) and ternary (AsSeI) systems.Studies of general physical properties of the binary system As-Se and the ternary system As-Se-I, and determination of the short wavelength limit, other optical properties and their microhardness, have recently been reported [1][2][3][4].With the use of Raman spectroscopy, it was established that the As-Se-I glasses with an As content below 2 at% and an I content below 10 at% consist of Sen chains and Se8 rings, and of AsI3 structural units statistically distributed between them.In a second group of glasses, corresponding to 2

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