Infrared spectra, band frequencies and structure of sodium germanate glasses

Infrared reflection spectra of vitreous GeO2 and xNn(2)O .(1-x)GeO2 glasses in the 0<x less than or equal to 18 and 24<x<33 composition regions (x being Nn(2)O content in mol%) were treated,vith dispersion analysis using the convolution model for the complex dielectric constant. Infrared band assignments are discussed based on a comparison with the spectrum of hexagonal GeO2 crystal and on the consideration of the band frequencies and oscillator strengths as the functions of glass composition. The 400-1000 cm(-1) range of spectra studied is interpreted in ter ms of the stretching modes of the Ge-O-Ge bridge and (for glasses belonging to the 24<x<33 region) of the Ge-O- terminal group. The frequency of a band related to the principal asymmetric stretching mode of the Ge-O-Ge bridge is shown to decrease gradually front 890 cm(-1) (for vitreous GeO2) down to 750 cm(-1) (for a glass with Na2O content of similar to 32 mol%). Weak bands observed in the spectra of vitreous GeO2 and low alkali glasses at the low and high wavenumber wings of the principal band are assigned to two additional asymmetric stretching modes of the Ge-O-Ge bridge For high alkali glasses the frequency of a single str etching mode of the Ge-O- terminal group is found to be higher than the frequency of the principal Ge-O-Ge asymmetric stretching mode (820-830 and 750-760 cm(-1), respectively).