Properties and Structure of Glasses in the System PbO‐GeO 2

Glasses are readily made from compositions containing up to 45 mol% PbO. The deviation of molar volume from ideality plotted vs composition shows a broad minimum at 70 to 80 mol% GeO 2 , similar to the behavior of the alkali‐GeO 2 glasses, indicating that the change in coordination of the Ge 4+ ion from 4‐ to 6‐fold occurs in this system, although maxima are not seen in plots of density and refractive index vs composition (mol%). Light scattering and electron microscopy indicate microstructure in glasses in the composition range 10 to 30 mol% PbO. This microstructure appears to affect the dc resistivity and viscosity but not the thermal‐expansion coefficients.