Structure role of cesium bromide in calcium silicate glasses and glass ceramics

To make the interpretation of the complex xCsBr.(100 − x)(CaO:SiO₂) glasses easier to study, the structure of glasses in a binary composition CaO-SiO₂ is being initially investigated. The changes in the crystallization behavior of glasses and the local environment surrounding silicon atoms could be easily followed using X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy. The XRD pattern of the binary 50CaO-50SiO₂ glass showed that its structure was amorphous. But when (CaO:SiO₂) is replaced with CsBr, some sharp diffraction lines appear in system of the ternary xCsBr.(100 − x)(CaO:SiO₂) glass composition. A Polycrystalline Cs₂Ca(SiO₃)₂ structure is the primary phase in CsBr rich glasses. The results based on transmission electron microscopy (TEM-EDP) and X-ray diffraction pattern (XRD) are in excellent agreement, indicating that crystalline-clustered species develop in glasses enriched with CsBr. Both the NMR and FTIR spectra are clearly defined, and they contain different features that distinguish between different silicate structural subunits. One and two bridging oxygen atoms (BO) can be found in the main SiO₄ structural units. Such units become less shielded due to increasing of non-bridging oxygen atoms (NBO) in the silicate network by increasing CsBr at the expense of both SiO₂ and CaO. There is a good correlation between the data obtained from FTIR and NMR spectroscopy. Both techniques could differentiate between BO and NBO involved in the silicate structural units. (author)