EPR STUDY OF LOW-SYMMETRY MN2- SUPERPOSITION MODEL AND CRYSTAL-FIELD ANALYSIS OF THE ZERO-FIELD SPLITTING PARAMETERS( CENTERS IN LINBO3 )

X-band EPR spectra of Mn2+:LiNbO3 single crystals at room temperature are analyzed with a spin-Hamiltonian of C-3 symmetry. Experimental dat a are interpreted using the superposition model in a twofold way. Firs tly, the zero-field splitting (ZFS) parameters b(2)(0), b(4)(0), b(3)( 4), and b(4)(-3) are predicted. While the results for b(2)(0) are not conclusive, those for the major fourth-order ZFS term \upsilon(4)(3)\ = [(b(3)(4))(2) + (b(4)(-3))(2)](1/2) indicate better agreement with e xperiment, assuming Mn2+ at the Nb site. Secondly, crystal field (CF) parameters are obtained from the superposition model using two sets of available structural data. Diagonalization of the CF Hamiltonian with in the whole 3d5 configuration yields the theoretical ZF splittings. T he results for Mn2+ at the Nb site agree better with the experimental data than those for Mn2+ at the Li site. Hence the superposition model analyses of the observed EPR spectra indicate that the spectra can be most likely attributed to Mn2+ ions at Nb sites. The ways to reconcil e this conclusion with the opposite one from the low temperature ENDOR study are discussed.