Dielectric and AC conductivity studies in Li2O-CoO-B2O3-TeO2 glasses

CoO and Li2O mixed with borotellurite glasses in the compositions, (B2O3)0.2-(TeO2)0.3-(CoO) x -(Li2O)0.5−x, where x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.50 were synthesized by fast cooling the melt to room temperature. Absence of crystalline phases in the samples was confirmed by X-ray diffraction studies. Changes in dielectric properties with frequency and temperature over wide ranges have been measured. Dielectric constant and loss increased with increase in CoO content. AC conductivity has been analyzed using Mott’s small polaron model and activation energy was determined. Activation energy decreased and conductivity increased with increase in CoO content up to 0.3 mole fractions, and they behaved oppositely for higher concentration of CoO. This observed change of trend in activation energy and conductivity at 0.3 mole fraction of CoO ascribed to switch over of conduction mechanism occurring from predominantly ionic to electronic regime. For the first time, a transition of conduction mechanism is observed in borotellurite glasses. Temperature and composition independent relaxation mechanism in these glasses has been confirmed by plotting the scaled conductivity master curves. Hunt’s model has been invoked to understand the frequency dispersion of conductivity.