Mixed Ion-Polaron Glasses as New Cathode Materials

Electrical transport in mixed ion-polaron glasses has been investigated in four series of glasses containing transition metal oxides (TMO) namely WO3/MoO3, and Na+/Ag+ ions with the composition xWO3- (30-0.5x)Na2O-(30-0.5x)ZnO-40P2O5, xWO3-(30- 0.5x)Ag2O-(30-0.5x)ZnO-40P2O5, xMoO3-(30-0.5x)Na2O- (30-0.5x)ZnO-40P2O5, and xMoO3-(30-0.5x)Ag2O-(30- 0.5x)ZnO-40P2O5, 0 ≤ x ≤ 60 (mol%). The DC conductivity of Na-glasses up to 30 mol% of WO3 and MoO3 is almost identical due to the dominance of ionic conductivity. In this compositional region, the introduction of tungstate and molybdate units increases the mobility of sodium ions and compensates the decrease in sodium number density. On the other hand, with increasing WO3 and MoO3 content and decreasing Ag+ ion concentration in Ag-glasses the DC conductivity decreases for few orders of magnitude. A significant difference in conductivity is observed for glasses with higher WO3 and MoO3 content. While for glasses containing WO3 the conductivity rapidly increases due to a huge polaronic contribution indicating a turnover from predominantly ionic to polaronic transport, the conductivity for MoO3- glasses decreases in the entire mixed compositional range suggesting dominant ionic transport. The changes in the conduction mechanism with the systematic alternation of the glass composition have been analyzed in correlation with the structural modifications and variations of molybdenum and tungsten in different oxidation states.