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

Abstract A series of tungsten–lead–germanate glasses with the x WO 3 ·(100 −  x )[7GeO 2 ·3PbO] composition where x  = 0, 1, 5, 10, 15, 20, 30, 40 mol% WO 3 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 [WO n ] structural units and the formation of PbWO 4 crystalline phase, in agreement with IR and XRD data, respectively. The cyclic voltammogram of the glass electrode with x  = 10 mol%WO 3 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.