Analytical determination of the local oxygen structure aroundCr3+inSnO2

Abstract

The origin of two distinct electron paramagnetic resonance (EPR) spectra observed in Cr-doped Sn02 crystals, i.e. , (EPR)l and (EPR)», was investigated using the superposition model specifically developed for rutile-type crystals. Analytical results suggest that these spectra are due to the substitutional Cr'+ ions having a unique structure with respect to its local surrounding oxygen atoms. The (EPR)l spectrum showed that the four nearest-neighbor oxygen atoms on the (110) plane have moved from normal sites toward the Cr + ion by 0.072 A (3.5%) as a result of a reduction in the metal ionic radius. The (EPR)» spectrum showed the Cr + ion to be coupled with the vacancy of the two nearest-neighbor oxygen atoms on the [110]axis. In this case, the ratio of spin-Hamiltonian parameters takes the form E/D = -cos2a from the superposition model, where a is the angle between the [001] axis and the cation-ligand bonding axis in (110) plane. The theoretical value E/D = -0.205 was obtained from this simple relation, and was in good agreement with the experimental values.

Theoretical studies of the local structure and the EPR parameters for substitutional Mo5+ in TiO2

“…The oxygen octahedra in both sites exhit significant low symmetrical distortions. For the substitutional site, the ligand octahedron is slightly elongated with two longer bond-lengths R || (≈ 1.99Å) parallel with the [110] axis and four coplanar shorter bond-lengthsR ⊥ (≈1.94Å) perpendicular to the axis, with the planar bonding angle θ of about 81 • [15].The above low symmetrical distortions can be characterized by the axial distortion angle ∆α = α − α 0 , with α ≈ tan −1 (R ⊥ /R // ) and α 0 ≈ 45 • of the cubic symmetry. Thus, we have ∆α ≈ −0.73 • for the host substitutional site [15].…”

“…For the substitutional site, the ligand octahedron is slightly elongated with two longer bond-lengths R || (≈ 1.99Å) parallel with the [110] axis and four coplanar shorter bond-lengthsR ⊥ (≈1.94Å) perpendicular to the axis, with the planar bonding angle θ of about 81 • [15].The above low symmetrical distortions can be characterized by the axial distortion angle ∆α = α − α 0 , with α ≈ tan −1 (R ⊥ /R // ) and α 0 ≈ 45 • of the cubic symmetry. Thus, we have ∆α ≈ −0.73 • for the host substitutional site [15]. Additionally, the ligand octahedron for this site also suffers large perpendicular (or rhombic) distortion characterized by the deviation ∆θ of the plannar bonding angle θ related to the cubic value θ 0 (=90 • ), i.e., ∆θ = θ − θ 0 = −9 • [15].…”

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

“…In the TiO 2 (rutile structure) crystal, the Ti 4+ ion is coordinated to a slightly elongated oxygen octahedron with two longer bond lengths R || (≈ 1.988Å [14]) parallel to the C 2 axis and four coplanar shorter bond lengths R ⊥ (≈ 1.944Å [14]) perpendicular to the axis with the axial distortion angle α ≈ tan −1 (R ⊥ /R || ). In addition, the planar bond angle θ (≈ 80.88 • [14]) inducing the rhombic distortion (i. e., δ θ = θ 0 − θ where θ 0 = 90 • is the value for an ideal octahedron).…”

“…In addition, the planar bond angle θ (≈ 80.88 • [14]) inducing the rhombic distortion (i. e., δ θ = θ 0 − θ where θ 0 = 90 • is the value for an ideal octahedron). When the impurity Cu 2+ is doped into the lattice of TiO 2 , it may replace the host Ti 4+ .…”

“…A 2 (R 0 ) andĀ 4 (R 0 ) are the intrinsic parameters with the reference distance R 0 (≈ 1.959Å), which is the metalligand distance related to the octahedral Ti 4+ site in the host TiO 2 crystal [14]. The ratioĀ 2 (R 0 )/Ā 4 (R 0 ) is in the range of 9 ∼ 12 [12, 21 -23]; we takeĀ 2 (R 0 ) ≈ 9Ā 4 (R 0 ) here.…”