Effect of TiO2 on electron paramagnetic resonance, optical transmission and dc conductivity of vanadyl doped sodium borate glasses

Glass systems with composition xTiO(2).(30 - x)Na2O.70B(2)O(3) (series I) and xTiO(2).(70 - x)B2O3.30Na(2)O (series II) containing 2 mol% V2O5 have been prepared (0 less than or equal to x less than or equal to 7, mol%) by normal melt-quenching. The electron paramagnetic resonance (EPR) spectra of VO2+ ions have been recorded in the X-band (similar to9.13 GHz) at room temperature. Spin Hamiltonian parameters, g(parallel to), g(perpendicular to), A(parallel to), A(perpendicular to), the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been calculated. The increase in Deltag(parallel to)/Deltag(perpendicular to) with increase in TiO2 content in series I shows that the octahedral symmetry of V4+O6 complex is reduced, whereas in series II the octahedral symmetry is improved with increase in x. The decrease in P, in both the series, indicates that the 3d(xy) orbit expands with increase in mol% of TiO2. The molecular orbital coefficients, alpha(2) and gamma(2) have been calculated by recording the optical transmission spectra in the range 500-850 nm. alpha(2) and gamma(2) increase with increase in x in both the series, which indicates that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity a, decreases and activation energy, W increases with increase in TiO2:Na2O ratio whereas with increase in TiO2:Na2O ratio the variation in sigma and W is within experimental error. (C) 2004 Elsevier B.V. All rights reserved.