Theoretical studies on the local structure and spin Hamiltonian parameters for Cu²⁺ ions in LiTaO₃ crystal

The local structure and spin Hamiltonian parameters (SHPs) g factors (g_x , g_y , g_z ) and the hyperfine structure constants (A_x , A_y , A_z ) for Cu²⁺ doped in the LiTaO₃ crystal are theoretically investigated by the perturbation formulas for a 3d⁹ ion under rhombically elongated octahedral based on the cluster approach. The impurity Cu²⁺ was assumed to occupy the host trigonally-distorted octahedral Li⁺ site and experience the Jahn-Teller (JT) distortion from the host trigonal octahedral [TaO₆ ]^10- to the impurity rhombically elongated octahedral [CuO₆ ]^10- . Based on the calculations, the impurity-ligand bond lengths parallel and perpendicular to the C₂ -axis are found to be R_|| (≈ 2.305 Å) and R_⊥ (≈ 2.112 Å) for the studied [CuO₆ ]^10- cluster, with the planar bond angle θ (≈ 78.2°). Meanwhile, the ground-state wave function for Cu²⁺ center in LiTaO₃ was also obtained. The calculated SHPs based on the above local lattice distortions agree well with the experimental data, and the results are discussed.