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

Structural and dynamical properties of lithium, cesium and mixed alkal i (i.e., lithium and cesium) berate glasses have been studied by the m olecular dynamics method. The calculations yield glass structures cons isting of planar BO3 triangles and BO4 tetrahedrons with no sixfold ri ng structures at all. Alkali ions show a strong preference to reside i n the vicinity of nan-bridging oxygen atoms, a tendency which is stron ger for lithium ions than for cesium ions. The experimental Raman peak s at 805 and 770 cm(-1) are reproduced by symmetric breathing modes of BO3 and BO4 units, respectively. Simulated infrared absorption spectr a reproduce the experimental spectra quite well. It appears that the v elocities of different cesium ions show much more correlation than tho se of the lithium ions and that the frequency spectra of Li+ and Cs+ i ons are in good agreement with far-infrared measurements.