Optical and electrical properties of lead silicate glasses

The optical and electrical properties of PbO-SiO₂ glasses containing 24.6 to 65 mole % PbO have been determined. While the short-wavelength cutoff increases continuously in wavelength with increasing PbO concentration, an abrupt lightening in color is observed in the vicinity of 38-40% PbO. The darker color of glasses containing 30-38% PbO has been associated with a scattering process. The origin of this scattering is discussed and is tentatively identified with the formation of microcrystals of SiO₂ in the glasses. The alternative process of liquid-liquid phase separation seems less likely, but cannot be ruled out with certainty. The electrical conductivity of all glasses investigated exhibits an Arrhenian temperature dependence. The activation energy decreases from about 1.23 eV for the 30% PbO composition to about 1.11 eV for the 50% PbO composition, and remains about constant for glasses containing higher concentrations of PbO. Addition of NH₄Cl or Sb₂O₃ to the batch or use of Pb(NO₃)₂ or Pb₃O₄ instead of PbO as a raw material does not affect the electrical properties. The dielectric constant at 1kHz increases continuously with increasing PbO concentration, from a value in excess of 20 for the 55% PbO composition. The implications of these results for the conduction mechanism in PbO-SiO₂ glasses are discussed.