STRUCTURAL STUDIES IN LEAD GERMANATE GLASSES - EXAFS AND VIBRATIONAL SPECTROSCOPY

The Raman, IR absorption and EXAFS spectra at the Ge K-edge and Pb L(I II)-edge of eight lead germanate glasses, with general formula x PbO(1 - x)GeO2 with x = 0.20, 0.25, 0.33, 0.40, 0.50, 0.53, 0.56 and 0.60, have been measured. The occurrence of [GeO6] units besides [GeO4] coul d not be deduced unambiguously from the data. The vibrational and EXAF S data agree with a progressive depolymerization of the network. Start ing from all Ge atoms linked to four bridging oxygens in GeO2 (X = 0), the number of tetrahedral units with one or two non-bridging oxygens increases with x. At low content, Pb2+ ions act as modifiers in the ge rmanate structure, but to a lesser extent than an equivalent number of alkaline ions.