Structural role of PbO in Li2O-PbO-B2O3 glasses

Thermal and spectroscopic studies have been carried out on a number of glas ses with wide ranging compositions in the pseudoternary glass system Li2O-P bO-B2O3 in order to understand the structural role of PbO in these glasses. Infrared, Raman, and B-11 MAS-NMR results indicate that PbO behaves as a n etwork former in these glasses and is possibly incorporated in the network as [PbO4/2](2-) units. The formation of [PbO4/2](2-) units leads to the cre ation of neutral three-coordinated boron (B-3(0)) which, in turn, leads to the reformation of four-coordinated boron (B-4(-)) in the structure at the expense of two-coordinated (B-2(-)) and singly coordinated (B-1(2-)) boron atoms. The variations of glass transition temperatures (T-g) and molar volu mes also Support this model. (C) 1999 Acadcmic Press.