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<Θ_D/4, where Θ_D is the Debye temperature) nor Greaves’ VRH model at intermediate temperatures (Θ_D/ 4<T<Θ_D/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 > Θ_D/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.

Acknowledgements

The authors are grateful to Inter University Consortium, Department of Atomic Energy Facilities (DAEF), Indore, India, for providing XRD and MDSC measurement facilities. We are also indebted to Tokyo Metropolitan Industrial Technology Research Institute, Japan, for their expertise in XPS assessment. This work was financially supported by University Grants Commission (UGC), Government of India, from UGC project (F. 10-31/98).

Notes

¶ Present address: Department of Physics, National Sun Yat Sen University, Kaohsiung 804, Taiwan.

Additional information

Notes on contributors

H. Sakata

¶ Present address: Department of Physics, National Sun Yat Sen University, Kaohsiung 804, Taiwan.