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

Abstract

The local structure and the spin Hamiltonian parameters (the g factors g i (i = x, y, z) and the hyperfine structure constants A i ) for Cu 2+ -doped Ca(OD) 2 are theoretically investigated from the perturbation formulas of these parameters for a 3d 9 ion in an orthorhombically elongated octahedron. From the studies, the planar Cu 2+ -OD -bonds are found to experience the relative variation 'R (|0.014 Å) along the X and Y axes, while those parallel to the Z axis may undergo the relative elongation 'Z (|0.25 Å) due to the JahnTeller effect. The theoretical spin Hamiltonian parameters based on the above local lattice distortions agree well with the experimental data. As compared with the previous treatments, the improvements of the theoretical spin Hamiltonian parameters are achieved in this work by adopting the uniform calculation formulas and the tetragonal field parameters based on the superposition model.

Investigation of the EPR parameters of the rhombic Cu2+center in (NH4)2Mg(SO4)2·6H2O single crystal

“…So the change of compressed Zn(H 2 O) 6 2+ octahedra in the host crystals to elongated Cu(H 2 O) 6 2+ octahedral in the impurity centers due to Jahn-Teller effect in Cu 2+ doped DHMS crystal can be understood. This point is also supported by the studies for Cu 2+ on the even original trigonally distorted Ca 2+ site in Ca(OD) 2 (14), which is actually surrounded by a rhombically elongated octahedron.…”

“…Here, t 2 ≈ 3 and t 4 ≈ 5 are the power-law exponents due to the dominant ionic nature of the bonds (14,(19)(20)(21).Ā 2 (R 0 ) andĀ 4 (R 0 ) are the intrinsic parameters with the reference distance R 0 (taken as R 0 =R = (R x + R y + R z )/3), with R i (i = x, y, z) is the metal-ligand distance along − x, − y, and − z axis, respectively. The ionic radius of Cu 2+ ( ≈ 0.72 Å) (22) is close to that of the replaced Mg 2+ ( ≈ 0.69 Å (23)).…”

“…Meanwhile, the higher cubic orbital triplet 2 T 2g would be split into three singlets 2 B 1g (ζ ), 2 B 2g (η) and 2 B 3g (ξ ) (14,15). It is noted that the previous studies (10) for 3d 9 ions under rhombically distorted octahedra normally failed to connect the EPR parameters with the local structures of impurity centers, and the ligand contributions were also neglected by adopting various adjustable molecular orbital coefficients.…”

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

“…Therefore, the observed Δg (≈ 0.32) and δg (≈ 0.049) are reasonably attributed to the axial bond angle distortion Δα (= α 0 -α ≈ 2.5 , here α 0 = 45 for a perfect octahedron) and the planar bond angle distortion δθ (= θ 0 -θ ≈ 11. 19,31,56,62 reveal that signs of the hyperfine structure constants for A x , A y are positive, and for A z is negative of the Cu 2+ centers under rhombically elongated octahedron. The negative sign of A z is mainly due to the larger magnitudes of the negative terms related to (κ -4a 2 /7) than those of the positive ones related to the anisotropic contributions.…”