Structure-property relations of caesium silicate glasses from room temperature to 1400 K: Implications from density and Raman spectroscopy

Abstract

This study investigated a series of caesium bearing silicate glasses with compositions ranging from 5 to 35mol. % Cs2O using Raman spectroscopy. The proportions of 4- and 3-fold SiO4 rings are estimated by using the relative intensities of the D1 and D2 vibrational bands in each spectra. An increase in the abundance of 3-fold SiO4 rings is apparent and confirms previous studies which proposed such a mechanism to be present with increasing alkali content in alkali silicate glasses. The behaviour of the D1 and D2 bands correlates with the density measurements lending credence to the importance of the formation 3-fold SiO4 rings with increasing molar volume in silicate glasses. The high frequency envelopes (∼800–1300cm−1) were modeled using Gaussian lineshapes in order to isolate the separate contributions to the convoluted peak shape. These Gaussian bands are interpreted as being representative of the Qn species and are linked to the depolymerization reaction. We observe an increase in Q2 species coupled with a decrease in Q4 species with increasing Cs2O content. We propose that proximity to modifier cations drastically changes the vibrational character of the different Qn species and due to this effect we have assigned our curve-fit bands to both Qn and QnM species. High-temperature measurements were also conducted to investigate pre-melting and melting effects on the structure of these glasses. We observed similar changes in the high frequency envelope and Qn species distribution with increasing temperature as we did for increasing alkali content. The creation of Q2 species above the melting point leads us to conclude that depolymerization occurs at the solid-liquid transition.