Novel insights into electrical transport mechanism in ionic-polaronic glasses

Transformation of electrical transport from ionic to polaronic in glasses, which are a potential class of new cathode materials, has been investigated in four series containing WO3/MoO3 and Li+/Na+ ions, namely: xWO(3)-(30-0.5x)Li2O-(30-0.5x)ZnO-40P(2)O(5), xWO(3)-(30-0.5x)Na2O-(30.5x)ZnO-40P(2)O(5), xMoO(3)-(30-0.5x)Li2O-(30-0.5x)ZnO-40P(2)O(5), and xMoO(3)-(30-0.5x)Na2O-(30-0.5x)ZnO-40P(2)O(5), 0 x 60, (mol%). This study reports a detailed analysis of the role of structural modifications and its implications on the origin of electrical transport in these mixed ionic-polaron glasses. Raman spectra show the clustering of WO6 units by the formation of W-O-W bonds in glasses with high WO3 content while the coexistence of MoO4 and MoO6 units is evidenced in glasses containing MoO3 with no clustering of MoO6 octahedra. Consequently, DC conductivity of tungstate glasses with either Li+ or Na+ exhibits a transition from ionic to polaronic showing a minimum at about 20-30 mol% of WO3 as a result of ion-polaron interactions followed by a sharp increase for six orders of magnitude as WO3 content increases. The formation of WO6 clusters involved in W-O-W linkages for tungsten glasses plays a key role in significant increase in DC conductivity. On the other hand, DC conductivity is almost constant for glasses containing MoO3 suggesting an independent ionic and polaronic transport pathways for glasses containing 10-50 mol% of MoO3.