RAMAN-STUDY OF THE STRUCTURE OF GLASSES ALONG THE JOIN SIO2-GEO2

In order to better understand the distribution of tetrahedra in multicomponent tetrahedral network structures of melts and glasses, the Raman spectra of binary SiO//2-GeO//2 glasses were investigated. A comparison was made of the Raman spectral features of the end-member glasses and their vibrational origins are discussed. The mixing of GeO//2 and SiO//2 melts results in a continuous random network structure of TO//4 tetrahedra (T equals Si, Ge) in the glass. Raman bands corresponding to the antisymmetric stretch ( nu //a//s) of oxygen in Ge-O-Ge, Si-O-Si and Si-O-Ge bonds are observed in the glasses having intermediate compositions along the SiO//2-GeO//2 join. The presence of three distinct nu //a//s (T-O-T) bands in the spectrum of a glass having Si/Ge of one reveals that a considerable degree of Si-Ge disorder exists in the glass. The presence of a single symmetric oxygen stretching band in the spectra of binary SiO//2-GeO//2 glasses indicates that the symmetric stretch modes ( nu //s) of oxygen in Si-O-Si, Si-O-Ge and Ge-O-Ge bonds are strongly coupled. Results of the present study support the assignment of the bands in the 900-1200 cm** minus **1 region of the aluminosilicate glass spectra to the nu //a//s (Al-O-Si) and nu //a//s (Si-O-Si) modes. In contrast to the alumino-silicate glasses, however, the SiO//2-GeO//2 glasses have a much higher degree of disorder of the network-forming cations.