AC conductivity of V₂O₅-TeO₂ glasses

The electrical conductivity and dielectric constant of V₂O₅-TeO₂ glasses of compositions 10-80 mol% V₂O₅ have been measured in the frequency range 0.1-100 kHz and in the temperature range 77-400K. A frequency dependence according to the relation sigma ( omega )=A omega ^s has been observed, and values of the exponent s are less than unity (between 0.95 and 0.80 depending on the composition). The data of AC conductivity have been analysed in the light of different theoretical models based on quantum-mechanical tunnelling (QMT) and hopping over the barrier (HOB). The analysis shows that neither QMT nor HOB models can explain the data quantitatively. A linear dependence of the conductivity and a temperature-independent s at low temperatures, and a non-linear increase of conductivity at higher temperatures for higher frequencies agree respectively with QMT and HOB models. It is difficult to estimate the absolute value of tau ₀ (characteristic relaxation time of the system) or to arrive at a definite conclusion about the conduction mechanism by the Butcher and Morys model (1973) owing to experimental uncertainties in the measured values epsilon '( omega ) and the lack of knowledge of epsilon _infinity . A detailed investigation of epsilon ' as a function of composition for these glasses has been made. A non-linear variation of dielectric constant with concentration has been observed. The abnormally high dielectric constant ( approximately 30) of the low composition V₂O₅-TeO₂ glasses may be attributed to the characteristic role played by the glass former, TeO₂.