Effect of MoO3 on electron paramagnetic resonance spectra, optical spectra and dc conductivity of vanadyl ion doped alkali molybdo-borate glasses

Alkali molybdo-borate glasses having composition xMoO(3)center dot(30 - x)M2O center dot 70B(2)O(3) and xMoO(3)center dot(70 - x)B2O3 center dot 30M(2)O (M = Li, Na, K) with 0 <= x <= 15 (mol%) doped with 2.0 mol% of V2O5 have been prepared in order to study the influence of MoO3 on electrical conductivity, electron paramagnetic resonance (EPR) and optical spectra. From EPR studies it is observed that V4+ ions in these samples exist as VO2+ ions in octahedral coordination with a tetragonal compression and belong to C-4V symmetry. The tetragonal nature and octahedral symmetry of V4+O6 complex increase as well as decrease depending upon the composition of glasses with increase in MoO3 but 3d(xy) orbit of unpaired electron in the VO2+ ion expands in all the glasses. The decrease in optical band gap suggests that there is an increase in the concentration of non-bridging oxygen's. From the study of optical transmission spectra it is observed that for all the glasses the degree of covalency of the sigma-bonding decreases with increase in MoO3 content and the degree of covalency of the pi-bonding also varies. These results based on optical spectroscopy are in agreement with EPR findings. It is found that dc conductivity decreases and activation energy increases with increase in MoO3:M2O (M = Li, Na, K) ratio in MoO3 center dot M2O center dot B2O3 glasses, whereas the conductivity increases and activation energy decreases with increase in MoO3:B2O3 ratio in xMoO(3)center dot B2O3 center dot M2O glasses, which is governed by the increase in nonbridging oxygen's. The variation in theoretical optical basicity, Ath is also studied. (C) 2013 Elsevier B.V. All rights reserved.