Structural role of lead in lead silicate glasses derived from XPS spectra

The X-ray photoelectron spectroscopy (XPS) spectra of lead silicate glasses with different PbO content were measured and analyzed and the structural role of lead in the glass is discussed. It was found that the binding energy of Pb4f(7/2) decreases with the increase of PbO content before the concentration of PbO reaches 40 mol% and is maintained cit a low constant when the PbO content is higher than 40 mol%. It was inferred that the polarizability of Pb is concentration-dependent and grows with the increase of PbO content in the glass. This suggests an increase in the covalent degree of Pb-O bond, which accounts for the formation of the PbO4 pyramid polymeric chain network. It is proposed that in the low PbO content region (PbO < 40 mol%), SiO2 is the main glass former and the three dimensional network built by SiO4 tetrahedra is still maintained, with PbO increase in the glass. PbO4 pyramids tend to assemble together to form another structure network. In the high PbO content region (PbO > 40 mol%), the three-dimensional network built by SiO4 tetrahedra is seriously destroyed; the PbO4 pyramid polymeric chains connect together through SiO4 tetrahedra to form the glass structure network skeleton.