Structural investigation of vanadium ions doped Li2O-PbO-B2O3-P2O5 glasses by means of spectroscopic and dielectric studies

In the present investigation we report the synthesis of a series of transparent glasses of composition 20Li(2)O-20PbO-45B(2)O(3)-(15-x) P2O5: xV(2)O(5) with eight values of x ranging from 0 to 2.5 mol%, and their characterization. X-ray diffraction (XRD) spectra reflected the amorphous nature of the glasses. Optical absorption, electron paramagnetic resonance (EPR) spectra and FTIR study of vanadyl ions in the present glass network have been analyzed. The optical absorption and EPR investigations have revealed that vanadium ions do exist in both V4+ and V5+ states and the redox ratio (V4+/V5+) is observed to increase with the increase in concentration of V2O5. Dielectric properties viz., dielectric constant epsilon' (omega), loss tan S, electrical moduli M'(omega), M ''(omega), a.c. conductivity sigma(ac) over an extensive scale of frequency and temperature have been investigated as a function of V2O5 concentration. The dispersion of dielectric constant epsilon' (omega) with temperature has been interpreted by space charge polarization model. The dielectric loss and electrical moduli variation with frequency and temperature exhibited relaxation effects. These effects are ascribed to V4+ ions. The a.c. conductivity of the prepared glasses is perceived to escalate with the hike in V2O5 concentration whereas the activation energy for conduction exhibits a reverse trend. The conductivity mechanism is explained on the basis of polaronic transfer between V4+ and V5+ ions. The low temperature a.c. conductivity mechanism is elucidated by the quantum mechanical tunneling model. The growth in the values of dielectric parameters with raise in the concentration of V2O5 is due to V4+ ions which act as modifiers. The investigation of these results has indicated that at higher concentrations of V2O5, the VO2+ ions in the glasses were present in octahedral sites with tetragonal compression and belong to Ctv symmetry. (C) 2014 Elsevier B.V. All rights reserved.