Chapter 9: PbO and SnO Germanate Glasses Check Access

Lead and tin germanate glasses do not exhibit the maxima in density and refractive index displayed by all other RO germanate glasses. The compositional dependence of the density and refractive index changes slope at about 30 mol% PbO, which is near the locations of the maxima in these properties in other RO germanate glasses. The elastic moduli of the lead germanate glasses exhibit maxima at 25 to 30 mol% PbO. The electrical conductivities of lead germanate glasses pass through a minimum at about 15 mol% PbO, followed by an increase of about 3 orders of magnitude. No explanation for this behavior is available. The glass transformation temperature and transformation range viscosity of lead germanate melts initially decreases with increasing PbO content, followed by a plateau between about 5 and 25 mol% PbO, followed by a monotonically decrease to the limit of glass formation. This plateau is attributed to the occurrence of phase separation. The density of thallium lead germanate glasses increases monotonically with decreasing GeO₂ content, while the glass transformation temperature decreases monotonically. The properties of sodium lead germanate glasses gradually change from those of the sodium germanate glasses to those of the lead germanate as PbO replaces Na₂O.