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

Abstract

Low melting Li 2 O-PbO-B 2 O 3 , Me 2 O-ZnO-B 2 O 3 , Me = Li, Na, K, Rb and CaO-ZnO-B 2 O 3 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 (N 4 ) of fourfold coordinated boron (B 4 ) 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 Li 2 O-PbO-B 2 O 3 . Alkali ions are mainly responsible for the formation of B 4 -units and metaborate. Zinc ions favorably compensate non-bridging oxygen and partially form ZnO 4 . With decreasing N 4 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 N 4 . • In alkali-zinc-borate glasses alkali ions mainly neutralize the charge of B 4 -units. • Zinc ions favorably compensate the charge of non-bridging oxygens in the glasses. • The number of tetrahedral boron depends on the nature of the network-modifier. • The type of alkali ion and Zn or Pb ion directs the formation of borate units. • Alkali-glasses reflect a decrease of Young's Modulus with atomic packing density.