Electrochemical characterization and structure of tungsten-lead-germanate glasses and glass ceramics

A series of tungsten-lead-germanate glasses with the xWO(3)center dot(100 - x)[7GeO(2)center dot 3PbO] composition where x = 0, 1, 5, 10, 15, 20, 30, 40 mol% WO3 were synthesized using melt quenching technique. Tungsten ions seem to exist in these glasses in the W+5 state acting as glass modifiers; this is evidenced from UV-vis, EPR spectra and cyclic voltametry measurements, too. Our results show that the lead and germanium atoms do not accommodate with the non-bridging oxygens and the excess of the oxygen ions. The accommodation of the network is possible by the increase of the amount of [WOn] structural units and the formation of PbWO4 crystalline phase, in agreement with IR and XRD data, respectively. The cyclic voltammogram of the glass electrode with x = 10 mol%WO3 exhibits two pairs of distinct maxima attributed to the reduction of Ag+1 to Ag-0, W+6 to W-0 and the oxidation of Pb+2 to Pb+4, W+5 to W+6. The semiconducting properties of these glasses are due to electron transfer between tungsten and lead ions with different valence states. (C) 2013 Elsevier Ltd. All rights reserved.