The formation of BO 4 − tetrahedra and nonbridging oxygen ions in borosilicate glasses with low silica content

Abstract

Alkali-, mixed alkali- and mixed alkali-alkaline earth aluminoborosilicate glasses with low silica content have been prepared and annealed. Molar volume measurements and structural analysis using X-ray diffraction, IR spectra, and UV-transmission were carried out. It is shown that the formation of nonbridging oxygen ions bonded with the silicon ions takes place during the formation of BO 4 − tetrahedra for 0.4⩽R⩽0.8 whereR is the alkali oxide to the boron oxide ratio. From X-ray diffraction patterns, it is found that no crystalline phases can be detected. The UV-transmission spectra elucidated that the probability of formation of nonbridging oxygen ions in the glass with a single alkali ion (Li+) is higher than that in the glass with mixed alkali ions (Li++K+) under the same conditions. It is assumed that the shift of the UV-edge to lower or longer wavelengths may be due to the phase separation process in these glasses.