Raman Studies of PbO-Bi₂O₃-Ga₂O₃ Glasses and Crystallised Compositions

The structure of PbO-Bi2O3-Ga2O3 glasses and crystallised compositions were investigated by Raman spectroscopy and x-ray diffraction analysis. The glasses have a network structure composed of three structural units; GaO4 distorted tetrahedra, BiO6 distorted octahedra and PbO4 and/or PbO3 pyramids present next to each other. The Raman spectra of crystalline PbO-Bi2O3-Ga3O3 compositions indicate that the lead oxide, β-PbO, crystallised first from the high lead content glasses. The formation of the crystalline β-PbO phase results from the isolation of chains of PbO4 pyramids which are loosely bonded to other units in the glass structure. The Raman spectra of crystalline high bismuth content compositions reveal the crystallisation of lead bismuth oxides, 2 PbO-3 Bi2O3 and PbO2-6 Bi2O3 and the oxidation of the Pb(II) to Pb (IV) ions with increasing crystallisation temperature. The decrease of the crystallisation temperature with increasing Bi2O3 content is attributed to highly distorted BiO6 octahedra present in the glass structure. Such highly distorted BiO6 octahedra can easily form crystalline com- pounds with lead oxide which suggests that majority of the bismuth and lead ions are present in the network modifier sites in the glass structure