Electrical transport studies in alkali borovanadate glasses

Abstract

The ac conductivity and dielectric behaviors of sodium borovanadate glasses have been studied over wide ranges of composition and frequency. The dc activation energies calculated from the complex impedance plots decrease linearly with the Na₂O concentration, indicating that ionic conductivity dominates in these glasses. The possible origin of low-temperature departures of conductivity curves (from linearity) of vanadium-rich glasses in log s versus 1/T plots is discussed. The ac conductivities have been fitted to the Almond-West type power law expression with use of a single value of s. It is found that in most of the glasses s exhibits a temperature-dependent minimum. The dielectric data are converted into moduli (M*) and are analyzed using the Kohlrausch-William-Watts stretched exponential function. The activation barriers, W, calculated from the temperature-dependent dielectric loss peaks compare well with the activation barriers calculated from the dc conductivity plots. The stretching exponent β is found to be temperature independent and is not likely to be related as in the equation β = 1 - s. An attempt is made to elucidate the origin of the stretching phenomena. It appears that either a model of the increased contribution of polarization energy (caused by the increased modifier concentration) and hence the increased monopole-induced dipole interactions or a model based on increased intercationic interactions can explain the slowing down of the primitive relaxation in ionically conducting glasses.