Role of CsBr in structure and properties of new cesium bromo-borate glasses

Abstract

Glasses of enlarged chemical composition in the xCsBr-(100-x)B2O3 system, with x = 30–80 mol% have been prepared and studied for the first time. The hydrothermal preparation method is used to prepare fine powdered samples. The X-ray Diffraction (XRD), Fourier Transform Infrared spectra (FTIR) and 11B Nuclear Magnetic Resonance (11B NMR) are the tools used to study the structure of glasses. Even at the high CsBr concentration (30–60 mol%), XRD results revealed an amorphous structure characterized most of the examined compositions. But glasses enriched with CsBr (70 and 80 mol%) possess some ordered sub-structures impeded in the main amorphous network. 11B NMR and FTIR spectroscopy confirmed the presence of BO3 triangle as the major and dominant structural units. The four coordinated boron (BO4), on the other hand, can't be detected in the all analyzed compositions. An extremely low concentration from BBr4 tetrahedral groups (boron coupled with Br) is formed. The B-O bonds of planar BO3 triangles, which are the fundamental units, were involved in the production of amorphous clusters of the type Cs4B5O9]Br. Density (D) measurement and calculating molar volume (Vm), packing density and free volume(Vf) have been studied. The added CsBr can't play a role of modifier but it might be inserted interstitially between the borate structural units causing increasing of molar volume and free space in the glass network structure. The results based on transmission electron microscopy (TEM-EDP) and X-ray diffraction pattern (XRD) are in good agreement, indicating that the amorphous-clustered species are developed in the studied glasses.