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

Electron paramagnetic resonance (EPR), optical properties and dc conductivity of xTiO(2)center dot(30 - x)R2O center dot 70B(2)O(3) and xTiO(2)center dot(70 - x)B2O3 center dot 30R(2)O (R = Li, K; 0 <= x <= 7, in mol%) glasses containing 2 mol% V2O5 have been studied. 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 evaluated. Decrease in Delta g(parallel to)/Delta g(perpendicular to) ratio with increase in TiO2 content in TiO2 center dot Li2O center dot B2O3 glasses show that the octahedral symmetry of V4+O6 comp lex is improved; whereas in TiO2 center dot K2O center dot B2O3 glasses, it is reduced with increase in x. The decrease in P, in both systems, 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 400-850 nm. alpha(2) and gamma(2) 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 (sigma) decreases and activation energy (W) increases with increase in TiO2:R2O ratio in TiO2 center dot R2O center dot B2O3 glasses whereas with increase in TiO2:B2O3 ratio in TiO2 center dot B2O3 center dot R2O glasses the variation in sigma and W is within experimental error