Structural Role of PbO in Li₂O–PbO–B₂O₃ Glasses

Abstract

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 [PbO_4/2]^2- units. The formation of [PbO_4/2]^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 (B^2-₁) boron atoms. The variations of glass transition temperatures (T_g) and molar volumes also support this model.