Investigations on the EPR parameters and defect structures due to Jahn-Teller effect for the Cu2+ and Ni+ centers in LiNbO3

The EPR parameters of the impurity Cu2+ and Ni+ in LiNbO3 are theoretically studied from the perturbation formulas for 3d9 ions under rhombically elongated and compressed octahedra, respectively. In both centers, the impurity Cu2+ and Ni+ ions was ascribed to occupy the host trigonally-distorted octahedral Li+ sites and the octahedrons experience the Jahn-Teller distortion from trigonal to rhombically -elongated and -compressed, respectively. The elongated [CuO6]10− cluster (and compressed [NiO6]11− cluster) are ascribed to suffering the axial elongation of 0.102 Å (and compression of 0.062 Å) along z-axis and the planar bonds are found to experience the relative variation of 0.023 Å (and 0.032 Å), respectively, due to the Jahn-Teller effect. The calculated EPR parameters based on the above lattice distortions agree reasonably with the experimental data, and the local structures of the impurity centers are discussed.