Electronic structure and properties of oxide glasses (I) π-Electron distribution on alkali borate glass networks

Abstract

Basicities of an oxygen in alkali borate glasses were estimated by means of SCF INDO LCAO-MO calculation for molecular models of various borate groups. The non-bonding levels of an oxygen with higher orbital energies were classified according to symmetry properties of the levels. One was the local π type (out-of-plane) molecular orbital primarily populating on a particular planar structure. The other was an in-plane lone pair. The degree of delocalization of the out-of-plane non-bonding level (π character) decreased in the composition region of 15–20 mol% alkali oxide, while in-plane basicity was nearly constant over the composition of 0–35 mol% alkali oxide. The π-type basicity of non-bridging oxygens in several kinds of borate ions was nearly equal to or smaller than those of bridging oxygens in tetraborate and diborate groups. Borate glasses were found to be inorganic π-electron systems, whose properties are largely controlled by the distribution of π electrons on their networks.