29Si and 207Pb NMR study of local order in lead silicate glasses

Binary lead silicate glasses have been investigated using Pb-207 and Si-29 high resolution solid state Nuclear Magnetic Resonance (NMR) spectroscopy. From these experiments we have evidenced that lead forms covalent PbO4 and PbO3 pyramids over a large compositional range. The distribution of the Q(n) silicate species is determined. The calculated equilibrium constant of the reactions 2Q(n) = Q(n+1) + Q(n-1) are 1 order of magnitude larger than those determined for alkali silicates. For both lead and silicon, there is a distribution of local environments. At larger lead contents, we observe the existence of a lead oxide based network. For <60 mol% PbO content, silicon is the main glass former. As the lead content increases, the silicate network is broken and the chains constituted of PbOn pyramids connect together. (C) 1998 Elsevier Science B.V. All rights reserved.