The structure of GeO2-SiO2 glasses and melts: A Raman spectroscopy study

We have investigated a series of glasses and melts along the GeO2-SiO2 join using in situ Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are 'regions' that are SiO2-like, GeO2-like and mixed GeO2-SiO2-like. Incorporation of GeO2 into the SiO2 network is initially accommodated via the 3- and 4-membered SiO4 rings which are lost as they convert to larger mixed Ge/Si rings. The LO-TO mode behavior is also consistent with a network that is composed of different 'regions' and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO4 rings and large SiO4 rings; the small 3- and 4-membered SiO4 rings are not reformed. (C) 2009 Elsevier B.V. All rights reserved.