RAMAN-SPECTROSCOPIC INVESTIGATION OF THE STRUCTURE OF SILICATE-GLASSES .4. ALKALI SILICO GERMANATE GLASSES

Raman spectra were measured on bulk Na2O.(2 - x)SiO2.xGeO2 glasses, where x varied from 0 to 2, and on Na2O.SiO2.xGeO2 glasses, where x varied from 0 to 1. Raman spectra were measured also on Na2.O.(1 - x)SiO2.xGeO2 glasses crystallized at 650-degrees-C, mostly a solid solution with the beta-Na2Si2O5 structure at x between 0 and 1.5. The spectra of the glasses as well as the crystalline solid solutions can be interpreted in terms of random substitution of Ge for Si. The symmetric stretching vibrations of the nonbridging bonds Si-O-, Ge-O-, -O-Si-O-, and -O-Ge-O- are localized and exhibit two-mode behavior. On the other hand, the symmetric stretchings of the bridging bonds Si-O-Si, Ge-O-Ge, and Si-O-Ge are coupled together to give only one Raman band as the Si/Ge ratio is varied.