ESR of Cu2+ in Ca(OD)2: Secondary spectra

Investigations on the local structure and spin Hamiltonian parameters for the orthorhombic Cu2+ center in Ca(OD)2

“…Third, the hyperfine structure constants were analyzed based on the four adjustable parameters, i.e., the dipolar hyperfine structure parameter, the core polarization constant, and two anisotropic parameters. Even though, the tetragonal approximation was adopted in the calculations, and the difference (or anisotropy) between A x and A y was not explained in the previous work [12]. Consequently, the previous results are not in good agreement with the experimental data, and the information on a defect structure in [12] seems insufficiently reliable for this center.…”

“…The Ca 2+ ion is in the center of the deutoxide octahedron formed by six ODligands, with the average cation-anion distance R ≈ 2.37 Å [14]. When a Cu 2+ ion is doped into the Ca(OD) 2 lattice, it may locate substitutionally on the Ca 2+ site due to the same charge [12]. As a Jahn-Teller ion, Cu 2+ within the deutoxide octahedron may suffer the Jahn-Teller distortions via the vibration interaction and exhibit the local structure different from that of the host Ca 2+ site in a pure crystal.…”

“…Nevertheless, the above local structure of the defect center might actually yield an approximately tetragonally compressed octahedron, which should exhibit g factors 2 ≤ g z < g x , g y [13]. Obviously, this point is opposite to the observed g factors g z > g x , g y > 2 [12]. Third, the hyperfine structure constants were analyzed based on the four adjustable parameters, i.e., the dipolar hyperfine structure parameter, the core polarization constant, and two anisotropic parameters.…”

“…Meanwhile, the covalency effect of Ca(OD) 2 :Cu 2+ was neglected by taking the orbital reduction factor as unit. Second, the previous structure analysis assumed that two OD -groups (labeled as 3 and 6 in [12]) along the quasi-tetragonal (or Z) axis (making 48° with respect to the crystalline c axis) move towards the central Cu 2+ by 0.234 Å, in consideration of the Jahn-Teller effect. Meanwhile, the other four nearest neighbor ligands along the X and Y axes within the (1 2 10) plane were supposed to shift away from Cu 2+ by 0.117 Å.…”

“…Thus, the EPR studies for Cu 2+ can provide important structural and electronic information of the doped materials and are of specific significance. For example, the EPR investigations have been carried out for Cu 2+ -doped Ca(OD) 2 , and the spin Hamiltonian parameters (the g factors g i (i = x, y, z) and the hyperfine structure constants A i ) were measured for one orthorhombic Cu 2+ center (spectrum II) [12]. To explain the above EPR results, the simple second order perturbation formulas of the spin Hamiltonian parameters for a 3d 9 ion under elongated octahedra were adopted in the previous work [12].…”