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

Abstract

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 $\beta$ 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 $\sigma$ bonding between the vanadium atom and equatorial ligands and of the $\pi$ bonding between vanadium atom and the vanadyl oxygen have been estimated.