Effect of TiO 2 on electron paramagnetic resonance, optical transmission and dc conductivity of vanadyl doped sodium borate glasses

Abstract

Glass systems with composition xTiO 2·(30− x)Na 2O·70B 2O 3 (series I) and xTiO 2·(70− x)B 2O 3·30Na 2O (series II) containing 2 mol% V 2O 5 have been prepared (0≤ x≤7, mol%) by normal melt-quenching. The electron paramagnetic resonance (EPR) spectra of VO 2+ ions have been recorded in the X-band (∼9.13 GHz) at room temperature. Spin Hamiltonian parameters, g ||, g ⊥, A ||, A ⊥, the dipolar hyperfine coupling parameter ( P) and the Fermi contact interaction parameter ( K) have been calculated. The increase in Δ g ||/Δ g ⊥ with increase in TiO 2 content in series I shows that the octahedral symmetry of V 4+O 6 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 TiO 2. The molecular orbital coefficients, α 2 and γ 2 have been calculated by recording the optical transmission spectra in the range 500–850 nm. α 2 and γ 2 increase with increase in x in both the series, which indicates that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity σ, decreases and activation energy, W increases with increase in TiO 2:Na 2O ratio whereas with increase in TiO 2:B 2O 3 ratio the variation in σ and W is within experimental error.