Structure of lead germanate glasses by Raman spectroscopy

Lead germanate glasses of the xPbO(1− x)GeO 2 compositions with x ranging from 0.200 to 0.625 have been synthesised and their crystallisation behaviour and vibrational properties studied by differential thermal analysis (DTA) and Raman spectroscopy. Raman spectra of the Pb 5Ge 3O 11 ceramics also have been measured and compared to lead germanate glass spectra and literature data on β-PbO. Ge atoms in low lead glasses are supposed to be surrounded by four to six oxygen atoms, while the high-lead glass ( x=0.625) corresponding to stoichiometry of the Pb 5Ge 3O 11 ferroelectrics contains predominantly fourfold coordinated germanium. Structural resemblence of high-lead germanate glasses to the Pb 5Ge 3O 11 crystal is proposed rather than to β-PbO. The `boson' peak range in the spectra of lead germanate glasses is discussed taking into account the similarities of the spectra of glassy and crystalline Pb 5Ge 3O 11.