The electron paramagnetic resonance (EPR) parameters (g factors g_i and the hyperfine structure constants A_i, i = x, y, z) are interpreted by using the perturbation formulae for a 3d^9 ion in rhombically (D_2h) elongated octahedra. In the calculated formulae, the crystal field parameters are set up from the superposition model, and the contribution to the EPR parameters from the admixture of d-orbitals in the ground state wave function of the Cu^2+ ion was taken into account. Based on the

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... lation, local structural parameters of the impurity Cu^2+ center in Cd_2(NH_4)_2(SO_4)_3 (CAS) crystal were obtained (i.e., R_x≈ 2.05 Å, R_y≈ 1.91 Å, R_z≈ 2.32 Å). The theoretical EPR parameters based on the above Cu^2+-O^2- bond lengths in CAS crystal show a good agreement with the observed values. The results are discussed.