Electron Paramagnetic Resonance Studies of VO2+ Ion Doped in Methyl Ammonium Gallium Alum Single Crystals

The electron paramagnetic resonance of the VO2+ ion in methyl ammonium gallium alum single crystals has been studied. It is observed that the VO+2 ion substitutes for the Ga3+ ion and forms a [VO(H2O)5]2+ complex, a distorted octahedron with a H2O vacancy along VO bond direction. The octahedron cubic axes are found to be displaced from crystallographic 〈001〉 axes by 9° in [110] plane. The EPR results suggest that the host alum probably belongs to β type in which the presence of VO2+ twists the octahedron cubic axes by about 9° from the crystallographic 〈100〉 axes. Optical absorption studies confirm the formation of [VO(H2O)5]2+. By correlating the EPR and optical absorption data, the covalency rates of σ bonding between the vanadium atom and equatorial ligands and of the π bonding between vanadium atom and the vanadyl oxygen have been estimated.