STRUCTURE OF PBO-BI2O3-GA2O3 GLASSES

The structure of PbO-BiO1.5-GaO1.5 glasses has been investigated by IR and Raman spectroscopy. An infrared absorption band involving four-coordinated Ga3+ ions was observed at about 610-650 cm-1. The peak of this band shifts toward higher wavenumbers with increasing GaO1.5 content, indicating that covalency of Ga-O bond increases with increasing GaO1.5 content. The peak deconvolution was made on Raman spectra of the glasses. The Raman bands at about 130 cm-1, 400 cm-1, 550 cm-1 and 650 cm-1, obtained by deconvolution, have been assigned to Pb-O or Bi-O, Ga-O-Pb or Ga-O-Bi, Ga-O-Ga, and Ga-O(non-bridging) vibrations, respectively. The presence of 550 cm-1- and 650 cm-1-band indicates that Ga3+ ions are coordinated by four oxygens. The much higher peak wavenumber of the 550 cm-1-band in the spectrum of BiO1.5-GaO1.5 glass compared with that in the spectrum of PbO-GaO1.5 glass is attributed to the much higher ionic field strength of Bi3+ ion compared with that of Pb2+ ion. The fraction of non-bridging oxygens in GaO4 tetrahedra decreases with increasing PbO and BiO1.5 contents. It is assumed that most Pb2+ and Bi3+ ions are network formers.