The EPR g factors g i (i = x, y, z) for the interstitial Ti 3+ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d 1 ion in rhombically compressed octahedra. The ligand octahedron in the impurity center is found to be less compressed than that on the host interstitial site due to the Jahn-Teller effect. The local compression parameter (≈0.026) and the rhombic distortion angle δφ (≈0.7 • ) around the impurity Ti 3+ are smaller than the host values (≈0.091 and 3.5 • ). The theoretical g factors based on the above local structural parameters are in good agreement with the experimental data. In addition, the g factors for a tetragonal interstitial Ti 3+ center are also reasonably interpreted.
The superhyperfine parameters T j ( j = x, y, z) for Cu 2+ in the squareplanar K 2 PdX 4 (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for an octahedral 3d 9 cluster, by considering both the contributions from the crystal-field and charge-transfer mechanisms. The related molecular orbital coefficients are determined from the cluster approach in a uniform way. Based on one adjustable proportional factor ρ for the orbital admixture coefficients, the calculated results of present work show reasonable agreement with the observed values.Keywords Electron paramagnetic resonance (EPR) · Superhyperfine interactions · Cu 2+ · K 2 PdX 4 (X = Cl, Br)
The spin Hamiltonian parameters and local structure for the tetragonal Rh 2+ center in rhombohedral BaTiO 3 are theoretically studied from the perturbation formulas of these parameters for a 4d 7 ion with low spin (S=1/2) in tetragonally elongated octahedra. This center is ascribed to substitutional Rh 2+ at the Ti 4+ site in BaTiO 3. The [ RhO 6]10- cluster suffers relative elongation (characterized by the elongation parameter ρ ≈ 0.9%) along the [100] axis due to the Jahn–Teller effect. The tetragonal elongation can entirely depress the slight trigonal distortion of the original Ti 4+ site in rhombohedral BaTiO 3. The calculated spin Hamiltonian parameters based on the above Jahn–Teller elongation show good agreement with the experimental results.
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