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 3d(9) 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 angstrom (and compression of 0.062 angstrom) along z-axis and the planar bonds are found to experience the relative variation of 0.023 angstrom (and 0.032 angstrom), 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. (C) 2018 Elsevier B.V. All rights reserved.