Alkali and alkaline earth zinc and lead borate glasses: Structure and properties

Abstract

Low melting Li₂O-PbO-B₂O₃, Me₂O-ZnO-B₂O₃, Me = Li, Na, K, Rb and CaO-ZnO-B₂O₃ glasses were studied with Raman and infrared spectroscopies to advance the structural understanding of zinc borate glasses as potential candidates for substitution of lead containing glasses.

Although the effect of type of alkali ions on the number (N₄) of fourfold coordinated boron (B₄) in the glasses is small, the alkali ions direct the type of borate groups, i.e., pentaborate in lithium, sodium, and calcium zinc borate glasses, as well as diborate in potassium and rubidium containing ones. Both groups were simultaneously found in Li₂O-PbO-B₂O₃. Alkali ions are mainly responsible for the formation of B₄-units and metaborate. Zinc ions favorably compensate non-bridging oxygen and partially form ZnO₄.

With decreasing N₄ and field strength of the alkali ions the atomic packing density, glass transition temperature and Young's Modulus also decrease. The coefficient of thermal expansion increases with decreasing N₄.