Polaronic conduction and dielectric relaxation dynamics in V2O5 added lead bismuth silicate glass system

V2O5 doped lead bismuth silicate glasses were prepared by melt quenching technique. Initially, the spectroscopic investigations viz., optical absorption (OA) and EPR spectral studies were performed; the results of these studies suggested reduction of a part of V5+ ions into V4+ ions (that are identified to form vanadyl complexes viz., VO2'). The results further indicated the largest concentration of such complexes in the glass doped with 0.6 mol % of V2O5. Infrared spectral (IR) results suggested a progressive disintegration of the augmented glass network with increase of V2O5 concentration beyond 0.3 mol%. Later, extensive investigations on dielectric properties were carried out. Values of dielectric permittivity, epsilon'(omega), loss tangent and a.c. conductivity, sigma(ac), observed to be minimal for the glass containing 0.3 mol% of V2O5 (V3 glass) and found to be increased for further increase of V2O5 content at any frequency and temperature. The electric moduli components exhibited dipolar relaxation effects. Relaxation time r for dipoles estimated from the spectra of electric moduli showed a decreasing trend as the V2O5 content increased up to 0.3 mol% and beyond that tau is found to be increased. The complexes of V4+ and Bi3+ ions with oxygen ions were predicted to be the possible dipoles responsible for the dipolar effects. A.c. conductivity variation with V2O5 concentration indicated the minimum for V3 glass and exhibited increasing trend as the content of V2O5 raised from 0.3 to 0.6 mol%. Quantitative analysis of this result indicated polaronic contribution to the conductivity (ascribed to mutual transfer of polarons between V4+ and V5+ ions) is prevalent in these glasses.