Vibrational spectra and structure of alkali germanate glasses

Numerous structural studies have been carried out so far to elucidate the nature of the so-called germanate anomaly but the correct structural model is still unknown. The objective of the present paper is to shed further light on the structure of alkali germanate glasses, namely those containing sodium and cesium oxides. Two series of glass samples were prepared, having molar 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 than or equal to 25). Polarized Raman and infrared absorption spectra were recorded for these glasses, as a function of the alkali content; infrared reflectivity measurements were also carried out and Kramers - Kronig analysis of the near-normal incidence spectra were compared with the polarized Raman spectra of the glasses. An overall Structural Picture has emerged, which is compatible with the presence of a fraction of higher coordinated Ge atoms, either five-fold or six-fold. (C) 2001 Elsevier Science B.V. All rights reserved.