Raman spectroscopic investigation of the structure and crystallization of binary alkali germanate glasses

Abstract

Raman spectra have been measured on bulk GeO2 glass and the alkali germanate glasses of composition M2OxGeO2 where M=K, Na, Li, and x varies from 19 to 1, as well as on crystallized glasses. The low alkali content glasses (x≥3) retain a completely polymerized structure of germania polyhedra. Addition of small amounts of alkali oxide to GeO2 glass does not break the Ge-O-Ge bridging bonds and creates higher co-ordination of germanium atoms. Further addition of alkali oxide eventually breaks up some of the Ge-O-Ge bonds to create Ge-O− non-bridging oxygens. In the K- and Na-glasses a small number of non-bridging oxygens already exist at x=4.5, while in the Li-glasses they do not exist even at x=4. The structures of the low alkali content glasses start to disappear at x between 4 and 3 and they disappear almost completely at x=2. At x between 2 and 1, glass structures become analogous to the silicate glass structures. At x=2, the glass consists of disordered (Ge2O5)n sheet-like structures and at x=1 disordered (GeO3)n chain structures.