• S Y Wu

      Articles written in Pramana – Journal of Physics

    • Theoretical evaluation of the electron paramagnetic resonance spin Hamiltonian parameters for the impurity displacements for Fe3+ and Ru3+ in corundum

      Q Fu S Y Wu J Z Lin J S Yao

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      The impurity displacements for Fe3+ and Ru3+ in corundum (Al2O3) are theoretically studied using the perturbation formulas of the spin Hamiltonian parameters (zero-field splitting and anisotropic 𝑔 factors) for a 3d5 (with high spin $S = 5/2$) and a 4d5 (with low spin $S = 1/2$) ion in trigonal symmetry, respectively. According to the investigations, the nd5 ($n = 3$ and 4) impurity ions may not locate at the ideal Al3+ site but undergo axial displacements by about 0.132 Å and 0.170 Å for Fe3+ and Ru3+, respectively, away from the center of the ligand octahedron along the C3 axis. The calculated spin Hamiltonian parameters based on the above axial displacements show good agreement with the observed values. The validity of the results is discussed.

    • Investigations on the local structure and 𝑔 factors for the interstitial Ti3+ in TiO2

      L H Wei S Y Wu Z H Zhang X F Wang Y X Hu

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      The EPR 𝑔 factors $g_{i}$ $(i = x, y, z)$ for the interstitial Ti3+ in rutile are theoretically studied from the perturbation formulas of these parameters for a 3d1 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 $(\approx 0.026)$ and the rhombic distortion angle $\delta \phi'$ $(\approx 0.7^{\circ})$ around the impurity Ti3+ are smaller than the host values ($\approx 0.091$ 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 Ti3+ center are also reasonably interpreted.

    • Studies of the 𝑔 factors and the superhyperfine parameters for Ni3+ in the fluoroperovskites

      Y X Hu S Y Wu X F Wang L L Li

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      The 𝑔 factors and the ligand superhyperfine parameters $A'$ and $B'$ for Ni3+ in KMgF3, CsCaF3 and RbCaF3 are theoretically studied from the formulas of these parameters for a 3d7 ion under octahedral environments in the weak field scheme. The unpaired spin densities for the fluorine 2s, 2p$_{\sigma}$ and 2p$_{\pi}$ orbitals are quantitatively determined from the molecular orbital and configuration interaction coefficients based on the cluster approach. The calculated results show good agreement with the experimental data, based on only one adjustable parameter (i.e., the proportionality factor 𝜌 related to the ligand s- and p-orbitals). The superhyperfine parameters for the axial and planar ligands in RbCaF3:Ni3+ are satisfactorily interpreted from the different impurity–ligand distances due to the elongation of the ligand octahedron during cubic-to-tetragonal phase transition.

    • Theoretical studies of the g factors and local structure for Pt3+ in 𝛼-Al2O3

      Z H Zhang S Y Wu S X Zhang L L Li

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      The anisotropic 𝑔 factors and local structure for the trigonal Pt3+ centre in 𝛼-Al2O3 are theoretically investigated from the perturbation formulas of the 𝑔 factors for a $5d^7$ ion in trigonal symmetry. The Pt3+ impurity is found to experience an outward displacement by about 0.18 Å away from the centre of the oxygen octahedron along the $C_3$-axis. The calculated g factors based on the above axial displacement show good agreement with the observed values. Importantly, the pending problem of $+3$ valence state of the doped Pt in 𝛼-Al2O3 is theoretically clarified, and the possibility of Pt+ ($5d^9$) is thus excluded in this work.

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