STRUCTURAL CHEMICAL PROCESSES AT THE SYNTHESIS OF CHALCOGENIDE GLASSES

Dissociation of structural units in glass-forming chalcogenide melts i s discussed for three different types of glasses: As2S3. AsSI and Ga2S 3-GeS2-AgX (X = Cl, Br, I). The process of dissociation was studied by means of chemical analysis, extraction, Raman and IR-spectroscopy and by investigation of crystallization products. The degree of dissociat ion in vitreous As2S3 was established as the transformation of AsS3/2 into As4S4 and SS2/2. In the case of AsSI, calculations were performed for the transformation of structural units AsS2/2I into AsS3/2 and As I3. It was found that the degree of dissociation of structural units i n As2S3 and AsSI depends upon the temperature of synthesis and the coo ling rate of the liquid. In a glass-forming system Ga2S3-GeS2-AgX, the fixed equilibrium of halogen exchange is supposed to occur according to the relationship: GeS4/2 + Ga2S3 + AgX = GeS(4-x/2)X-x + AgGaS2(1 l ess than or equal to x greater than or equal to 4). The degree of comp leteness of this reaction is connected with the compositions of struct ural units and the halogen. The results obtained are discussed,togethe r with thermodynamic data concerning heat of formation for different c ompounds in the systems under investigation.