Non-adiabatic small-polaron hopping conduction in VN–PbO–TeO2 glasses

Abstract

The dc conductivity of VN–PbO–TeO2 glasses with different mole percentages of VN, PbO and TeO2 has been measured in the temperature range 125–450 K. The conductivity of the glasses increases with increasing VN content for a fixed mole percentage of PbO. Neither Mott's variable-range hopping (VRH) model at low temperatures (T<ΘD/4, where ΘD is the Debye temperature) nor Greaves’ VRH model at intermediate temperatures (ΘD/ 4<T<ΘD/2) describe the dc conductivity data for these glasses. Multiphonon tunnelling transport of strongly coupled electrons is also unable to account for the carrier transport. However, at high temperatures (T > ΘD/2), conduction is shown to be due to small-polaron hopping in the non-adiabatic regime. Alteration of the VN content causes a change in the model parameters achieved from best-fitting curves for the glasses. Modulated differential scanning calorimetry analysis shows that the glass transition temperatures T g in this system vary from 269 to 302°C.