Alkali and alkaline earth zinc and lead borate glasses: Structure and properties
Lina Heuser, Marianne Nofz
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.