AN ELECTRON-SPIN-RESONANCE STUDY OF VANADIUM-DOPED ALPHA-TEO2 SINGLE-CRYSTALS

An ESR study of vanadium-doped paratellurite indicates that vanadium e nters the lattice as V4+, equally populating the four inequivalent cat ion sites. The 3d(1) electron exhibits hyperfine interaction with the I = 7/2 V-51 nucleus and superhyperfine interaction with two neighbour ing I = 1/2 nuclei identified as protons by ENDOR experiments. Spin Ha miltonian parameters computed from ESR measurements show that each V4 ion has a single C-2 symmetry axis along one of the [110] directions. The neighbouring hydrogens appear to enhance the symmetry and stabili ty of the defect structure. Group theoretical arguments show that ther e are two possible linear combinations of d wavefunctions that could r epresent the ground state of V4+ in alpha-TeO2. However, a determinati on of the lower-lying state was not feasible using only the ESR data.