The structure of thallium containing germanate and borate glasses

N. Laorodphan*, E. R. Barney, R. Dupree, J. V. Hanna, A.P. Howes and D. Holland

Thallium containing glasses are of interest due to their non-linear optical response, which relate to the thallium (1+ oxidation state) structural environment. It is suggested that the lone pair of electrons on thallium can be either stereochemically active or inactive depending on the composition of the glasses. NMR is a useful technique to examine the environment of thallium as both 203Tl and 205Tl nuclei are NMR active. Both Tl isotopes have nuclear spin I=½ and both have large gyromagnetic ratios, which make it easy to obtain a signal. In this study, germanate (xTl20•(100-x)GeO2) and borate (xTl20•(100-x)B2O3) glasses with x = 5-50% mol thallium oxide were investigated by both 205Tl solid-state NMR and neutron diffraction. A comparison of the structures of thallium germanate and thallium borate glasses will be presented. The ‘germanate’ and ‘borate’ anomalies are observed but are modified by the presence of increasing amounts of [:TlO3] trigonal pyramids with their associated lone-pairs.