EXPERIMENTAL AND THEORETICAL INVESTIGATION OF SPIN-HAMILTONIAN PARAMETERS FOR THE LOW-SYMMETRY FE3+ CENTER IN LINBO3

X-band EPR spectra of Fe3+ in LiNbO3 single crystals at room temperatu re are analyzed with a spin-Hamiltonian of C-3 symmetry. First the zer o-field splitting (ZFS) parameters b(2)(0), b(4)(0), b(4)(3), and b(4) (-3) are calculated using the superposition model (SPM). The SPM-ZFS r esults for Fe3+ at the Nb site agree better with the experimental ones than those for Fe3+ at the Li site. Next the crystal field (CF) param eters are predicted using SPM and two sets of available structural dat a for LiNbO3. Diagonalization of the full Hamiltonian, including the C F Hamiltonian, within the whole 3d(5) configuration yields the ZF spli ttings for Fe3+ centres. The ZF splittings obtained from the theoretic al SPM-CF calculations for Fe3+ at the Nb site agree better with the e xperimental EPR data than those for Fe3+ at the Li site. The present r esults indicate that the observed EPR spectra of Fe3+ :LiNbO3 can be a ttributed to Fe3+ ions at the Nb sites.