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

• Published in: Journal of molecular structure Vol. 1060; pp. 182 - 190
• Main Authors: Agarwal, A., Khasa, S., Seth, V.P., Sanghi, S., Arora, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 24.02.2014
• Subjects: Activation energy; Borate glasses; Compressing; Covalence; Direct current; Electron paramagnetic resonance; EPR; Glass; Ionic conduction; Optical properties; Spectra; Symmetry; Vanadyl ion; Borate glasses; Ionic conduction; Vanadyl ion; EPR; Optical properties
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2013.12.041

•V4+ ions exist as VO2+ ion in octahedral coordination with a tetragonal compression.•3dxy orbit of unpaired electron in VO2+ ion expands with increase in MoO3 content.•The results based on optical spectroscopy are in agreement with EPR findings.•The optical band gap decreases with increasing MoO3 content. Alkali molybdo-borate glasses having composition xMoO3·(30−x)M2O·70B2O3 and xMoO3·(70−x)B2O3·30M2O (M=Li, Na, K) with 0⩽x⩽15 (mol%) doped with 2.0mol% 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 C4V 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 3dxy 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 σ-bonding decreases with increase in MoO3 content and the degree of covalency of the π-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·M2O·B2O3 glasses, whereas the conductivity increases and activation energy decreases with increase in MoO3:B2O3 ratio in xMoO3·B2O3·M2O glasses, which is governed by the increase in nonbridging oxygen’s. The variation in theoretical optical basicity, Λth is also studied.