The role of vanadium valence states and coordination on electrical conduction in lithium iodide borate glasses mixed with small concentration of silver iodide

LiI–AgI–B2O3 glasses mixed with different concentrations of V2O5 (ranging from 0 to 1.0 mol%) were prepared. Electrical and dielectric properties over wide ranges of frequency (10−2–107 Hz) and temperature (173–523 K) have been studied. Additionally spectroscopic properties viz., optical absorption and ESR spectra have been investigated. The optical absorption and ESR studies have revealed that vanadium ions do exist in both V4+ and V5+ states and the redox ratio is the highest in the glasses containing 0.8 mol% of V2O5. The results of conductivity measurements have indicated that there is a mixed conduction (both ionic and electronic). The ionic conduction seems to be dominant over polaron hopping only in the glasses containing V2O5 more than 0.8 mol% of V2O5. The impedance spectra have also indicated that the conduction is predominantly polaronic in nature. The frequency and temperature dependence of the electrical moduli as well as dielectric loss parameters have exhibited relaxation character attributed to the vanadyl complexes. The relaxation effects have been analyzed by the graphical method and from this analysis it has been established that there is a spreading of relaxation times. The results have been further discussed quantitatively in the light of different valance states of vanadium ions with the aid of the data on spectroscopic properties.