Vibrational spectra and structure of alkali germanate glasses

Numerous structural studies have been carried out so far to elucidate the n ature of the so-called germanate anomaly but the correct structural model i s still unknown. The objective of the present paper is to shed further ligh t on the structure of alkali germanate glasses, namely those containing sod ium and cesium oxides. Two series of glass samples were prepared, having mo lar compositions (100 - x)GeO2 . xM(2)O (M = Na and 0 less than or equal to x less than or equal to 35, or M = Cs and 0 less than or equal to x less t han or equal to 25). Polarized Raman and infrared absorption spectra were r ecorded for these glasses, as a function of the alkali content; infrared re flectivity measurements were also carried out and Kramers - Kronig analysis of the near-normal incidence spectra were compared with the polarized Rama n spectra of the glasses. An overall Structural Picture has emerged, which is compatible with the presence of a fraction of higher coordinated Ge atom s, either five-fold or six-fold. (C) 2001 Elsevier Science B.V. All rights reserved.