Single and multiphonon assisted hopping conduction in CoO−TeO₂−V₂O₅ glasses

Glasses having a broad range of compositions in the system 10CoO.(90−x)TeO₂.xV₂O₅, are prepared and investigated. DC conductivity, density, and molar volume are studied. The conduction mechanism is found to be non-adiabatic in nature. The activation energy for conduction, W, is found to be less than that of TeO₂−V₂O₅ glasses containing Sn, Pb, and Bi oxides. Mott's model for the small polaron hopping conduction between nearest neighbours gives unreasonable values for the decay parameter of the wave function of the electron in the low valence state. The increase in the conductivity with temperature is interpreted in terms of the Schnakenberg model for an optical multi-phonon assisted hopping process at high temperatures and single optical phonon process at the lower ones. This model gives reasonable values for the phonon frequency, decay parameter, the polaron hopping energy, and slightly higher values of W _D. The density of glasses investigated decreases linearly with increasing V₂O₅ content. Each oxide contributes a specific factor to the glass density.