EPR Studies of VO²⁺ in Single Crystals of BaCl₂·2H₂O and BaBr₂·2H₂O

The EPR on single crystals of BaCl 2 ·2H 2 O and BaBr 2 ·2H 2 O doped with vanadyl ions are studied in the temperature range 30°C to -196°C. At room temperature the hyperfine structure of vanadium is observed. The spectrum at room temperature is isotropic and shows that vanadyl is tumbling in the lattice. The spectrum at low temperatures is also angular independent and the characteristics show that the motions of vanadyl are hindered. The spectra are analysed using a spin-Hamiltonian corresponding to tetragonal symmetry. The dependence of the linewidth on the nuclear-spin quantum number is studied and the linewidths at room temperature are found to obey the relation \(1/T₂{=}π√3(a₁+a₂mI+a₃mI²)\). The linewidth is found to increase at low temperature which is due to the increase in the correlation time.