Hydroxyl groups in germanosilicate glasses

The absorption band corresponding to the fundamental stretching vibration of hydroxyl (OH) groups in (GeO2)x(SiO2)1−x glasses with x≲25 mol% made by VAD and MCVD methods and by melting of GeO2 and SiO2 powders is investigated; literature data are analysed and quantum-chemical calculations of various possible OH groups structures in the atomic network of germanosilicate glass are performed. OH groups are shown to occur in the investigated specimens mainly as Si–OH silanol groups, the concentration of Ge–OH groups being less than 5%. The maximum at 3600 cm−1 of OH absorption band in germanosilicate glass usually ascribed to Ge–OH groups is supposed to be caused by Si–OH groups hydrogen-bonded with Ge–O–Ge and Si–O–Ge linkages. The apparent discrepancy of available literature data for various specimens of germanosilicate glasses is explained by the assumption that different manufacturing conditions yield different degree of homogeneity of glass specimens. The shape and position of the absorption bands of OH stretching vibration in GeO2–SiO2 glasses are proposed as an additional criteria of homogeneity of glass for technological control.