Structure of Vitreous Lithium and Cesium Triborates

摘要

Glasses of the compositions Li2O · 3B2O3 and Cs2O · 3B2O3 have been investigated using X-ray diffraction. The isomorphous substitution of heavy cesium for light lithium makes it possible to rather accurately determine the B-O and O-O interatomic distances in the lithium-containing glass and the Cs-Cs interatomic distances in the cesium-containing glass. For the Li2O · 3B2O3 glass, ten coordination shells are observed in the ordering region up to 7 A. A comparison of the experimental and model atomic radial distribution functions has revealed that the structure of the glass contains groups similar to those observed in crystalline LiB3O5. They include at least two triborate groups bound via the oxygen atom. For the Cs2O · 3B2O3 glass, ten coordination shells are revealed in the ordering region up to 12 A. An analysis of the experimental atomic radial distribution curve in the framework of the fragmentary model has allowed the conclusion that cavities similar to those inherent in crystalline CsB3O5 are retained in the structure of the cesium-containing glass and contain up to three cesium atoms located at distances close to the corresponding distances in the crystal. The statistical mean coordination of the cesium atoms by oxygen atoms remains unchanged.