Gel growth and characterization of pure and vanadyl-doped strontium tartrate tetrahydrate single crystals

Pure and vanadyl-doped single crystals of SrC4H4O6·4H2O (SrTr·4H2O) were grown by controlled diffusion in silica gel. The crystals were characterized by EPR and electronic absorption techniques. The angular variation EPR spectra showed that the VO2+ ion has a fixed orientation in the lattice. The g and A tensors and their direction cosines were evaluated from the EPR analysis. The above parameters for the observed sites were analysed assuming a spin Hamiltonian corresponding to a tetragonal symmetry. Electronic absorption studies carried out at 300 K as well as at 80 K showed three characteristic absorption bands at 12 500, 13 201 and 18 348 cm-1 which were assigned to crystal field (d-d) transitions and the site symmetry of the ion has been estimated to be tetragonal. To confirm the ascribed transitions, the band positions were calculated by solving the energy expressions corresponding to the tetragonal symmetry and compared with the observed band positions. The crystal field parameters (Dq) and tetragonal distortion parameters (Ds and Dt) were obtained from the best fit of the observed and calculated band positions. The EPR and electronic spectral results showed that the VO2+ ion has occupied the interstitial site having C4V symmetry. © 1985 Chapman and Hall Ltd.