EPR STUDY OF VO2-CENTER-DOT-H2O SINGLE-CRYSTAL( AND CR3+ IN LI2SO4)

A single crystal X-band EPR study of VO2+ and Cr3+ in Li2SO4 . H2O was carried out at room temperature. Analysis of the spectra indicates th at VO2+ substitutes for Li+ and that there are two magnetically inequi valent Li+ sites. The charge compensation occurs by removal of a neigh boring Li+. The principal values of the g and A tensors of the spin Ha miltonian for the two sites were determined. Superhyperfine interactio n of the 3d(1) electron of VO2+ with the neighboring water protons in the unit cell was observed and found to be between 0 and 0.5 mT, depen ding on the orientation of the magnetic field. Two magnetically differ ent sites were also observed for Cr3+, and the results were explained by a rhombic spin Hamiltonian. The Hamiltonian parameters g, D, and E were determined. It is concluded that VO2+ and Cr3+ enter into the Li places and the charge is compensated by a Li+ vacancy in the VO2+ cas e and proton vacancies in the Cr3+ case.