Theoretical explanation of EPR parameters for Cu 2+ ion in TiO 2 crystal

The gyromagnetic factors g , g ⊥ and the hyperfine structure constants A and A ⊥ of the tetragonal Cu 2+ center in KTaO 3 are theoretically studied in this work. Based on the analyses of the electron paramagnetic resonance results of this center, it is found that the impurity Cu 2+ occupies the octahedral Ta 5+ site, associated with a nearest-neighbouring oxygen vacancy V O along the C 4 axis. Due to the electrostatic repulsion of V O , Cu 2+ is displaced away from V O by ∆ Z(≈ −0.29Å) along the C 4 axis. The theoretical values of the g and A factors based on the above defect structure and the impurity displacement agreee reasonably with the experimental data.

Section: Discussionsupporting

confidence: 84%

“…Based on the theoretical calculations in this work and various observed results for Cu 2+ in some elongated oxygen octahedra [18,20,21], we suggest that these signs may be negative.…”

Section: Calculationssupporting

confidence: 64%

Theoretical Studies on the Gyromagnetic Factors and the Hyperfine Structure Constants for the Tetragonal Copper Center in KTaO₃

Dong

2005

“…In fact, expansion of the planar impurity-ligand distances leads to a slight decrease in the difference between the bonding lengths parallel with and perpendicular to the four-fold axis, and hence in tetragonal dis-tortion, yielding a larger (or better) value of the calculated g ⊥ . Although the sign of the experimental A was not determined in [8], theoretical studies in this work support the negative sign of A , as did some similar EPR investigations on Cu 2+ in elongated oxygen octahedra [22,23].…”

Section: Discussionsupporting

confidence: 73%

Investigations of the Defect Structure for Cu²⁺ in SrLaAlO₄

Wei

Dong

2005

The defect structure for Cu 2+ in SrLaAlO 4 is theoretically investigated by the perturbation formulas of the spin Hamiltonian parameters (g factors g , g ⊥ and the hyperfine structure constants A and A ⊥ ) for a 3d 9 ion in tetragonally elongated octahedra. Based on these studies, the tetragonal center may be attributed to Cu 2+ occupying the host Al 3+ site, associated with one hole delocalized at the four oxygen ligands in planar coordination. Furthermore, the four Cu,O bonds (perpendicular to the four-fold axis) are found to suffer an outward stretch of about 0.06Å due to (i) the local tenseness in this plane, arising from the size mismatching substitution of the smaller Al 3+ by the larger Cu 2+ and (ii) the weaker electrostatic attraction of the less charged Cu 2+ acting upon the four oxygen ions containing the delocalized hole. The calculated spin Hamiltonian parameters agree well with the experimental data. The defect structure of this center is discussed.

“…(iii) Unlike the studied Cu 2+ center on Ti 4+ site in [7,12] without charge compensation, the studied impurity center in this work is Cu 2+ at the 5-fold coordinated octahedral Ti 4+ site associated with one oxygen vacancy V O along the C 2 axis. The above different local structures for Cu 2+ in TiO 2 may be attributed to the different experimental preparation conditions.…”

Section: Discussionmentioning

confidence: 94%

“…Decades ago, the EPR spectra of Cu 2+ -doped TiO 2 crystals were measured [11] and attributed to the impurity Cu 2+ occupying the 6-fold coordinated octahedral Ti 4+ site with no charge compensation despite charge mismatch between the host Ti 4+ and the impurity Cu 2+ . The EPR parameters and the local lattice distortion for this Cu 2+ center were also investigated [7,12]. Whereas, recently, Brant et al proposed a new model for the impurity Cu 2+ doped in TiO 2 crystals, they suggested that the impurity Cu 2+ is at the 5-fold coordinated octahedral Ti 4+ site associated with one oxygen vacancy V O along the C 2 axis forming the Cu 2+ -V O center due to the charge compensation (see Fig.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Studies on the Local Structure and Electron Paramagnetic Resonance Parameters for Cu²⁺ Centers in TiO₂ with one Oxygen Vacancy Adjacent

Zheng

2013

Based on the defect model that the impurity Cu 2+ in TiO 2 on the octahedral Ti 4+ site is associated with one oxygen vacancy V O along the C 2 axis, the electron paramagnetic resonance (EPR) parameters, i. e., the g factors g i (i = x, y, z) and the hyperfine structure constants A i , of the Cu 2+ -V O center in TiO 2 are calculated by using the perturbation formulas of these parameters for a 3d 9 ion in a rhombically elongated octahedra. From this study, the impurity Cu 2+ is found to be away from V O by a distance ∆z (≈ 0.33Å) along the C 2 axis, meanwhile the four O 2− ions in the plane perpendicular to the C 2 axis may be shifted by ∆x (≈ 0.28Å) towards V O due to the electrostatic interaction between these ions and V O . The theoretical results based on the above local structure distortions show good agreement with the experimental data.