The Nature of Al-O Bonds in K₂O-Al₂O₃-B₂O₃ Glasses

Abstract

The nature of Al-O bonds in K₂O-Al₂O₃-B₂O₃ glasses has been studied by using the optical absorption spectra of VO²⁺ ions dissolved in the glasses. It has been found that the Al-O bonds in the glasses involve a double-bond character found only in the Al-O bonds in a structure unit containing a four-coordinated Al atom. The bonding mode of Al atoms in the glasses has been discussed in the light of the information obtained from the X-ray emission spectra for some aluminoborate glasses. Two modes have been suggested to be considered. In a mode, the only K⁺AlO₄- group is formed independently of the glass composition and, in the other, the K⁺(K⁺AlO₆^-)^- group, together with an AlO₄, is formed in the low K₂O region and the K⁺AlO₄^- group is dominantly formed at the high K₂O content.