SI-29 AND PB-207 NMR-STUDY OF LOCAL ORDER IN LEAD SILICATE-GLASSES

Binary lead silicate glasses have been investigated using Pb-207 and S i-29 high resolution solid state Nuclear Magnetic Resonance (NMR) spec troscopy. From these experiments we have evidenced that lead forms cov alent PbO4 and PbO3 pyramids over a large compositional range. The dis tribution of the Q(n) silicate species is determined. The calculated e quilibrium constant of the reactions 2Q(n) = Q(n+1) + Q(n-1) are 1 ord er 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 bas ed network. For <60 mol% PbO content, silicon is the main glass former . As the lead content increases, the silicate network is broken and th e chains constituted of PbOn pyramids connect together. (C) 1998 Elsev ier Science B.V. All rights reserved.