ELECTRICAL-TRANSPORT STUDIES IN ALKALI BOROVANADATE GLASSES

The ac conductivity and dielectric behaviors of sodium borovanadate gl asses have been studied over wide ranges of composition and frequency. The de activation energies calculated from the complex impedance plot s decrease linearly with the Na2O concentration, indicating that ionic conductivity dominates in these glasses. The possible origin of low-t emperature departures of conductivity curves (from linearity) of vanad ium-rich glasses in log sigma versus 1/T plots is discussed. The ac co nductivities have been fitted to the Almond-West type power law expres sion 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 dat a 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 c ompare well with the activation barriers calculated from the de conduc tivity plots. The stretching exponent beta is found to be temperature independent and is not likely to be related as in the equation beta = 1 - s, An attempt is made to elucidate the origin of the stretching ph enomena. 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 mo del based on increased intercationic interactions can explain the slow ing down of the primitive relaxation in ionically conducting glasses.