STRUCTURE AND DYNAMICS OF ALKALI BORATE GLASSES - A MOLECULAR-DYNAMICS STUDY

Structural and dynamical properties of lithium, cesium and mixed alkali (i.e., lithium and cesium) borate glasses have been studied by the molecular dynamics method. The calculations yield glass structures consisting of planar BO3 triangles and BO4 tetrahedrons with no sixfold ring structures at all. Alkali ions show a strong preference to reside in the vicinity of nan-bridging oxygen atoms, a tendency which is stronger for lithium ions than for cesium ions. The experimental Raman peaks at 805 and 770 cm(-1) are reproduced by symmetric breathing modes of BO3 and BO4 units, respectively. Simulated infrared absorption spectra reproduce the experimental spectra quite well. It appears that the velocities of different cesium ions show much more correlation than those of the lithium ions and that the frequency spectra of Li+ and Cs+ ions are in good agreement with far-infrared measurements.