Paramagnetic Resonance Spectra Of VO2 Research Articles

Investigations of the electron paramagnetic resonance spectra of VO2+ in CaO-Al2O3-SiO2 system

The EPR spectra for VO2+ in CaO-Al2O3-SiO2 system are calculated using complete diagonalization method (CDM) and perturbation theory method (PTM). The calculated results are in good agreement with the observed values. By comparing the calculated results by CDM and PTM in a wide range of crystal field parameters, the validity of the PTM formulas has been studied. It is shown that, the PTM formulas are reasonable and reliable in a wide range of CF parameters.

Structural investigations of vanadyl doped Nb2O5·K2O·B2O3 glasses

Pottasium nioborate glasses of composition xNb2O5·(30-x)K2O·69B2O3 containing 1 mol % of V2O5 were prepared by melt quench technique (1473K, 1h). The electron paramagnetic resonance spectra of VO2+ in these glasses have been recorded in X- band (v ≈ 9.14 GHz) at room temperature (RT). The spin Hamiltonian parameters, dipolar hyperfine coupling parameters, P and Fermi contact interaction parameter, K have been calculated. It is found that V4+ ions in these glasses exist as VO2+ in octahedral coordination with a tetragonal distortion. The tetragonality of V4+O6 complex decreases with increasing Nb2O5: K2O ratio and also there is an expansion of 3dXY orbit of unpaired electron in the vanadium ion. The study of IR transmission spectra over a range 400- 4000 cm-1 depicts the presence of both BO3 and BO4 structural units and Nb5+ ions are incorporated into the glass network as NbO6 octahedra, substituting BO4 groups.

Single-crystal EPR study of VO 2+ in Ba 2 Zn(HCOO) 6 .4H 2 O

The electron paramagnetic resonance spectra of VO2+ doped dibarium zinc formate tetrahydrate single crystals and powders were investigated at room temperature. The angular variations of the spectra indicated that the VO2+ enters Ba2+ and Zn2+ sites in their respective host crystals. The spin-Hamiltonian parameters were determined at room temperature. The g and A tensors were found to be axially symmetric for the powder sample (g⊥ = 1.987 ± 0.002, g∥ = 1.938 ± 0.002, A⊥ = 65 ± 2 and A∥ = 187 ± 1 Gauss), whereas they showed deviations from axial symmetry for the single-crystal sample.

Effect of vanadium and cobalt ions on electrical conductivity and EPR in sodium borate glasses

Glasses with composition xCoO · (0.3–x)Na2O · 0.70B2O3 have been prepared over the range 0 · x · 0.12 containing 1 mol%/2 mol% of V2O5. Electron paramagnetic resonance spectra of VO2+ of the glasses have been measured at X-band (v · 9.3 GHz) at room temperature. Spin Hamiltonian parameters of the VO2+ ions have been calculated. It is found that for x · 0.05 the octahedral symmetry is reduced when Na2O is replaced by CoO. d.c. conductivity of these samples has also been measured which shows that conductivity decreases and activation energy increases when Na2O is replaced by CoO.

Electron paramagnetic resonance in CoO.CaO.B2O3glasses containing vanadium ions

Abstract Glasses with composition × CoO.(0.25-x) CaO.0.75 B2O3 have been prepared over the range 0 ≤ x ≤ 0.25 containing 2 mol% of V2O5. Electron paramagnetic Resonance spectra of VO2+ of these glasses has been measured at X-band (ν ≈ 9.15 GHz) at room temperature and at liquid nitrogen temperature. Spin Hamiltonian parameters of the VO2+ ions have been calculated. It is found that for x ≤ 0.12 the octahedral symmetry of the V4+ site is improved. A part of these glasses were annealed at 473 K for 24 hours and EPR spectra were recorded and analysed.

Vanadyl binding to a testicular S-100-like protein and to calmodulin: Electron paramagnetic resonance spectra of VO2+-protein complexes

The binding of vanadyl to a porcine and bovine testicular S-100-like protein and to calmodulin was demonstrated using X-band (9.2 gHz) electron paramagnetic resonance (EPR) spectroscopy in aqueous solution at pH 7.4. In liquid solutions at 22°C, the vanadyl-protein complexes yielded VO2+ near rigid limit spectra. At 122 K, each of the three high-field resonances (i.e., 3/2, 5/2, and 7/2 parallel components) splits into two components indicating the presence of two classes of vanadyl-binding sites in each protein. The spectra of the frozen solutions were simulated to give parallel and perpendicular components of the hyperfine coupling constant and g factors similar to other vanadyl-protein complexes.

Electron Paramagnetic Resonance Studies of VO2+ Doped in KAl(SO4)2·12H2O and NH4Al(SO4)2·24H2O Single Crystals

The electron paramagnetic resonance spectra of VO2+ ions doped in KAl(SO4)2·12H2O and NH4AL(SO4)2·24H2O single crystals are studied. In both the crystals it is observed that VO2+ ion substitutes for an Al3+ ion and forms a [VO(H2O)5]2+ complex, forming a distorted octahedron with an H2O vacancy along the VO bond direction. The octahedron axes are found to coincide with the crystallographic 〈100〉 axes, indicating that the presence of VO rotates the octahedron axes so as to coincide with the crystallographic axes. The formation of the vanadyl pentahydrate complex has been further confirmed by taking an optical-absorption spectrum. By correlating the EPR and the optical-absorption data, the covalency rates of σ bonding between the vanadium atom and the equitorial ligands and of the π bonding between the vanadium atom and the vanadyl oxygen have been estimated. All the spectra are analyzed by using the usual spin-Hamiltonian method.