Study of EPR, optical properties and dc conductivity of VO2+ ion doped TiO2⋅R2O⋅B2O3 (R = Li and K) glasses

• V4+ ions exist as VO2+ ions in octahedral coordination and belong to C4V symmetry.
• Tetragonal nature of V4+O6 complex varies with TiO2 content.
• 3dxy orbit of unpaired electron in VO2+ expands with increase in TiO2 content.

Electron paramagnetic resonance (EPR), optical properties and dc conductivity of xTiO2⋅(30 − x)R2O⋅70B2O3 and xTiO2⋅(70 − x)B2O3⋅30R2O (R = Li, K; 0 ⩽ x ⩽ 7, in mol%) glasses containing 2 mol% V2O5 have been studied. Spin Hamiltonian parameters, g‖, g⊥, A‖, A⊥, the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been evaluated. Decrease in Δg‖/Δg⊥ ratio with increase in TiO2 content in TiO2⋅Li2O⋅B2O3 glasses show that the octahedral symmetry of V4+O6 complex is improved; whereas in TiO2⋅K2O⋅B2O3 glasses, it is reduced with increase in x. The decrease in P, in both systems, indicates that the 3dxy orbit expands with increase in mol% of TiO2. The molecular orbital coefficients, α2 and γ2 have been calculated by recording the optical transmission spectra in the range 400–850 nm. α2 and γ2 increase with increase in x in all glasses expect KB glasses, which indicate that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity (σ) decreases and activation energy (W) increases with increase in TiO2:R2O ratio in TiO2⋅R2O⋅B2O3 glasses whereas with increase in TiO2:B2O3 ratio in TiO2⋅B2O3⋅R2O glasses the variation in σ and W is within experimental error.

Variation of Log σ versus 103 T−1 for xTiO2⋅(70 − x)B2O3⋅30Li2O glasses.Figure optionsDownload as PowerPoint slide