Thermal, acoustic, and nuclear magnetic resonance studies of cesium borate glasses

The purpose of this study was to compare the physical properties and structure of cesium borate glasses. Cesium borate glasses can be denoted as RCs2O·B2O3, where R is the molar ratio of cesium oxide to boron oxide. We report a detailed study of the glass transition temperature (Tg) of these cesium borate glasses with 0.0⩽R⩽0.55. Initially, the Tg increased monotonically as R rose. It then leveled out at R=0.35 and fell at R=0.425. The Tg data obtained using a differential scanning calorimeter (DSC) are in good agreement with Kodama et al.ʹs Tg results from a differential thermal analyzer (DTA) as well as Chryssikosʹ model of the number of bridging oxygens per boron (Z). We determined the fraction of boron atoms in tetrahedral co-ordination, N4, for the same cesium borate glass samples using 11B NMR. The N4 fractions followed a curve similar to that of the Tg results until R=0.45, where it continued to rise as the Tg fell. Also, the N4 data have a similar trend but are consistently higher than those calculated from a model which employed Kodama and Kojimaʹs ultrasonic velocity data. Finally, the NMR data do not display a significant lowering of the N4 fraction in cesium borate when compared to lithium borate glasses.