A study was made of structures and ionic transport in fluoroborate glasses. Particular attention was paid to samples with an equimolecular composition. The X-ray absorption fine-structure data indicated that the Pb atoms were well distributed throughout the glass network. The results of 19F nuclear magnetic resonance measurements indicated that the F- ions were mobile in this glass. However, because a direct comparison between nuclear magnetic resonance data and conductivity was not possible, the possibility that a contribution to the conductivity was made by other species could not be completely eliminated. On the other hand, it was unclear what these species could be; because the Pb2+ ions were not normally mobile in ionic solids and the O2- ions were part of the framework. The conductivity of the equimolecular glass was found to be higher here than had previously been reported. It was similar, in absolute magnitude and activation energy, to the conductivity of a glass with 30mol%B2O3. The difference was attributed to differences in the nominal and actual compositions (because this glass was difficult to analyze). Overall, the conductivity increased markedly with increasing fluoride content at low fluoride concentrations. Thus, an increase from 30 to 50mol%PbF2 increased the conductivity by some 3 orders of magnitude. It was suggested that this was because the number of mobile fluoride ions increased in a super-linear fashion, or because there was an increase in the F- ion mobility with increasing fluoride content.

M.Teke, A.V.Chadwick: Materials Science Forum, 1997, 239-241, 421-4