Structural chemical processes at the synthesis of chalcogenide glasses

Dissociation of structural units in glass-forming chalcogenide melts is discussed for three different types of glasses: As2S3, AsSI and Ga2S3–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 dissociation 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 AsI3. It was found that the degree of dissociation of structural units in As2S3 and AsSI depends upon the temperature of synthesis and the cooling 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)/2Xx+AgGaS2 (1≤x≥4). The degree of completeness of this reaction is connected with the compositions of structural units and the halogen. The results obtained are discussed, together with thermodynamic data concerning heat of formation for different compounds in the systems under investigation.