An investigation on the defect structures and spin Hamiltonian parameters for the two orthorhombic Ti3+ centers in ZnWO4

作者：Ding, Chang-Chun^*; Wu, Shao-Yi; Zhu, Qing-Sheng; Zhang, Zhi-Hong; Teng, Bao-Hua; Wu, Ming-He

来源：Journal of Physics and Chemistry of Solids, 2015, 86: 141-147.

DOI：10.1016/j.jpcs.2015.06.017

• Electron paramagnetic resonance

By employing the perturbation formulae of the spin Hamiltonian parameters (SHPs) (g factors g(xx), g(yy), g(zz), hyperfine structure constants A(xx), A(yy), A(zz) and superhyperfine parameters A(xx)', A(yy)', A(zz)' ) for a 3d(1) ion in orthorhombically elongated octahedra and tetrahedra, the defect structures and the experimental EPR spectra are theoretically and systematically investigated for the two orthorhombic Ti3+ centers C-1 and C-2 in ZnWO4. Center C-1 is ascribed to the impurity Ti3+ at host W6+ site associated with two nearest neighbor oxygen vacancies due to charge compensation. The resultant tetrahedral [TiO4](5-) cluster is determined to undergo the local orthorhombic elongation distortion, characterized by the axial distortion angle Delta theta (=theta-theta(0) approximate to -6.84 degrees) of the local impurity-ligand bond angle theta related to theta(0) ( approximate to 54.74 degrees) and the perpendicular distortion angle Delta epsilon (=epsilon-epsilon(0) approximate to 2.5 degrees) related to so ( approximate to 45 degrees) of an ideal tetrahedron because of the Jahn-Teller effect. Center C-2 is attributed to Ti3+ on Zn2+ site, and this octahedral [TiO6](9-) cluster may experience the local axial elongation Delta Z ( approximate to 0.001 angstrom) and the planar bond angle variation Delta phi ( approximate to 9.1 degrees) due to the Jahn-Teller effect, resulting in a more regular oxygen octahedron. All the calculated SHPs (i.e., g factors for both centers, the hyperfine structure constants for center C-2 and superhyperfine parameters of next nearest neighbor ligand W for center C-1) show good agreement with the observed values. However, the theoretical results based on the previous assignment of center C-1 as Ti3+ on W6+ site with only one nearest planar oxygen vacancy (i.e., five-fold coordinated octahedral [TiO5](7-) cluster) show much worse agreement with the experimental data. The defect structures and the SHPs (especially the g anisotropies) are discussed for both centers. The present studies on the superhyperfine parameters of ligand W6+ for center C-1 would be helpful to further investigations on the superhyperfine interactions of cation ligands which were rather scarcely treated before.

• 出版日期2015-11
• 单位电子科技大学