RAMAN STUDIES OF PBO-BI2O3-GA2O3 GLASSES AND CRYSTALLIZED COMPOSITIONS

The structure of PbO-Bi2O3-Ga2O3 glasses and crystallised compositions were investigated by Raman spectroscopy and x-ray diffraction analysi s. The glasses have a network structure composed of three structural u nits; GaO4 distorted tetrahedra, BiO6 distorted octahedra and PbO4 and /or PbO3 pyramids present next to each other The Raman spectra of crys talline PbO-Bi2O3-Ga2O3 compositions indicate that the lead oxide, bet a-PbO, crystallised first from the high lead content glasses. The form ation of the crystalline beta-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 conten t compositions reveal the crystallisation of lead bismuth oxides, 2PbO -3Bi(2)O(3) and PbO2-6Bi(2)O(3) 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 attr ibuted to highly distorted BiO6 octahedra present in the glass structu re Such highly distorted BiO6 octahedra can easily form crystalline co mpounds with lead oxide which suggests that majority of the bismuth an d lead ions are present in the network modifier sites in the glass str ucture.