Cation-Network Interactions in Binary Alkali Metal Borate Glasses. A Far-Infrared Study
The far-infrared spectra of compositions probing the glass-forming regions of all five binary alkali metal borate systems χM2O.(1-χ)B2O3 (00.25.One distribution of cation sites has been observed for the lower alkali metal content Rb and Cs glasses.The fractions of cations in the two different network sites have also been evaluated.The squares of the frequencies of the cation-motion bands were found to vary linearly with composition, and exhibit kinks at χ ca. 0.20, for all but the Cs glasses.This behavior was explained on the basis of the network structural changes known to occur at this composition.
Kamitsos, E. I.,Karakassides, M. A.,Chryssikos, G. D.
Borate glass structure by Raman and infrared spectroscopies
Raman and infrared spectroscopies have been employed to probe the continuous evolution of borate glass structures as a function of the nature and concentration of alkali oxide modifiers.At relatively low alkali contents, the glasses contain covalent networks consisting of interconnected units bearing BO4- tetrahedra.Further addition of alkali oxide causes the progressive depolymerization of the network as a result of the formation of non-bridging oxygen atoms.Eventually, complete network disruption into small and highly charged borate units results in ionic glasses.The nature of the alkali cation determines the structure of these glasses by affecting several high-temperature isomerization or disproportionation equilibria.