ESR investigation of transition metal defects in KNbO₃

Abstract

Using ESR, we identified Fe3+ in the rhombohedral phase of the photorefractive compound KNb03. Fe3+-Vo was found in the orthorhombic as well as the rhombohedral phases. The spectra were analysed and compared to those of Fe3+ and Fe3+-Vo in other oxide compounds, e.g. BaTi03. A superposition model analysis yielded information on the geometry of Fe3+ and its nearest neighbours. Also CO*+, Coz+-Vo and Ir4+ were identified, analysed and compared to corresponding findings in other oxide hosts.

Explanation of the g-factors and Hyperfine Structure Constants of Co2+ in Tetragonal K2ZnF4

“…Many studies for the optical and paramagnetic properties of 3d" ion in K 2 ZnF 4 crystal were made [1][2][3], Among them, the g factors g n g ± and the hyperfine structure constants A,, A ± for Co 2+ in K 2 ZnF 4 were measured from EPR experiments decades ago [3], but until now no theoretical explanations have been made for them. The reason may be the lack of an effective calculation method for the EPR parameters of the 3d 7 ion in tetragonal octahedral crystals. Abragam and Pryce [4] established the second-order perturbation formulas of g, and A, for 3d 7 ions in axial (tetragonal and trigonal) symmetry.…”

“…The reason may be the lack of an effective calculation method for the EPR parameters of the 3d 7 ion in tetragonal octahedral crystals. Abragam and Pryce [4] established the second-order perturbation formulas of g, and A, for 3d 7 ions in axial (tetragonal and trigonal) symmetry. Although these formulas are often quoted and applied in many works [5-81, there are three problems in them: (i) The configuration interaction (CI) due to the admixture of ground state with the excited states is considered in these formulas, but the covalency (CO) effect due to the admixture between the d electrons of the central 3d 7 ion and the p electrons of ligands is neglected, (ii) There are several adjustable parameters.…”

“…Although these formulas are often quoted and applied in many works [5-81, there are three problems in them: (i) The configuration interaction (CI) due to the admixture of ground state with the excited states is considered in these formulas, but the covalency (CO) effect due to the admixture between the d electrons of the central 3d 7 ion and the p electrons of ligands is neglected, (ii) There are several adjustable parameters. (iii) For Co 2+ (3d 7 ) in the elongated ligand octahedron the assumption Ag (= g ± -g N )<0, is not correct. So, these formulas cannot yield reasonable results of g : and Afor 3d 7 ions in crystals.…”

“…(iii) For Co 2+ (3d 7 ) in the elongated ligand octahedron the assumption Ag (= g ± -g N )<0, is not correct. So, these formulas cannot yield reasonable results of g : and Afor 3d 7 ions in crystals. On the other hand, by considering CO effect, Tinkham [9] established first-order and Robbroeck et al [10] developed second-order perturbation formulas of g t and A, for 3d 7 ions in rhombic (also including tetragonal) symmetry.…”

“…In order to overcome the above difficulties, in this paper we present a cluster approach to the calculation formulas of g, and A, for 3d 7 ions in tetragonal octahedral crystals. In these formulas, the role of CI and CO effects is considered (note: because of the large spin-orbit coupling coefficient of the Co 2+ ion, the role of the JahnTeller effect is not important and should be neglected for Co 2+ in octahedra [11][12][13], as made in many previous papers [4][5][6][7][8][9][10]).…”