Electrical conduction and dielectric properties of vanadium phosphate glasses doped with lithium

AC conductivity and dielectric studies on vanadium phosphate glasses doped with lithium have been carried out in the frequency range 0.2-100 kHz and temperature range 290-493 K. The frequency dependence of the conductivity at higher frequencies in glasses obeys a power relationship, sigma(ac) = Aomega(s). The obtained values of the power s lie in the range 0.5 less than or equal to s less than or equal to 1 for both undoped and doped with low lithium content which confirms the electron hopping between V4+ and V5+ ions. For doped glasses with high lithium content, the values of s less than or equal to 0.5 which confirm the domination of ionic conductivity. The study of frequency dependence of both dielectric constant and dielectric loss showed a decrease with increasing frequency while they increase with increasing temperature. The results have been explained on the basis of frequency assistance of electron hopping besides the ionic polarization of the glasses. The bulk conductivity increases with increasing temperature whereas decreases with increasing lithium content which means a reduction of the V5+. (C) 2002 Published by Elsevier Science Ltd.