Structural Role of PbO in Li2O–PbO–B2O3 Glasses

Thermal and spectroscopic studies have been carried out on a number of glasses with wide ranging compositions in the pseudoternary glass system Li2O–PbO–B2O3 in order to understand the structural role of PbO in these glasses. Infrared, Raman, and 11B MAS-NMR results indicate that PbO behaves as a network 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 creation of neutral three-coordinated boron (B03) 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 (B2−1) boron atoms. The variations of glass transition temperatures (Tg) and molar volumes also support this model.