Structural, physical and thermal properties of lead germanate glasses

The effects of PbO concentration on the density, thermal and structural properties of xPbO-(100-x)GeO2 (x = 20 to 55 mol%) glasses were studied. Density of glasses increases linearly from 5.043 to 6.981(5) g center dot cm(-3), while the glass transition temperature decreases drastically from 467 degrees C to 359 degrees C on increasing PbO concentration from 20 to 55 mol%. Neutron diffraction studies found that Ge-O co-ordination is in the range: 3.9-4.2(1), and there is a very weak germanate co-ordination anomaly at PbO concentration of 40 and 50 mol%. GeO4 are the dominant structural units with a small quantity of GeO3 and GeO5 but very little GeO6 in the glass network. Pb-O and O-O co-ordination decreases with an increase in PbO mol% and are in the range of: 4.0-3.1(1) and 6.3-5.4(1) respectively. Raman studies indicate a decrease in Pb-O co-ordination with increase in PbO mol%, in good agreement with the neutron diffraction findings.