XAS investigation of tantalum and niobium in nanostructured TiO2 anatase

Sacerdoti, M.; Dalconi, Maria Chiara; Carotta, M.C.; Cavicchi, B.T.; Ferroni, Matteo; Colonna, Stefano; Vona, Maria Luisa Di

doi:10.1016/j.jssc.2003.12.015

Cited by 50 publications

(12 citation statements)

References 22 publications

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“…3B). This provides the evidence that Nb ions exist as Nb 5+ [8] and release conduction electrons with an efficiency of >90% up to n Nb¨1 .7 Â 10 21 cm À 3 (x¨0.06). At higher dopant concentration n Nb¨2 .9 Â 10 21 cm À 3 (x¨0.1), the ionization efficiency decreases slightly, possibly because a portion of the Nb ions become tetra-valent.…”

Section: Transport Propertiesmentioning

confidence: 65%

Novel transparent conducting oxide: Anatase Ti1−xNbxO2

et al. 2006

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Section: Transport Propertiesmentioning

confidence: 65%

Novel transparent conducting oxide: Anatase Ti1−xNbxO2

et al. 2006

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“…Normalized intensities of O K-edge features were analyzed in order to examine the electronic structure of the conduction band in TTO x films annealed at different temperatures. The qualitative energetic order of the corresponding hybridized molecular orbitals between Ti 3d, 4sp, and O 2p are characterized18,19 as 2t 2g (Ti 3d; O 2pp) < 3e g (Ti 3d; O 2pr) < 1a 1g (Ti 4s; O 2pr) < 3t 1u (Ti 4p; O 2pp). After normalization, the relative intensity can explain the transition of an electron from the O 1s orbital to the unoccupied Ti 3d and 4sp orbitals of TiO x using empirical symmetry-determined models.…”

mentioning

confidence: 99%

The effect of Ta doping in polycrystalline TiOx and the associated thin film transistor properties

Park

Chung

et al. 2013

Applied Physics Letters

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Tantalum (Ta) is suggested to act as an electron donor and crystal phase stabilizer in titanium oxide (TiO x). A transition occurs from an amorphous state to a crystalline phase at an annealing temperature above 300 C in a vacuum ambient. As the annealing temperature increases from 300 C to 450 C, the mobility increases drastically from 0.07 cm 2 /Vs to 0.61 cm 2 /Vs. The remarkable enhancement of thin film transistor performance is suggested to be due to the splitting of Ti 3d band orbitals as well as the increase in Ta 5þ ions that can act as electron donors.

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“…65 The result shows that the electronic population of Nb Ti is about 4.7e less than that of the Nb atom, which is consistent with the experimental nding that substitutional Nb ions exist as Nb 5+ in Nb-doped anatase. 66 This suggests that a substitutional Nb atom provides more electrons than a host Ti atom does (4+) to the system and thus act as donors for n-type conductivity. The slightly lower than the nominal 5+ valency of Nb Ti also suggests charge transfer from Nb to Ti, which contributes to lowering the CBM against the Fermi level.…”

Section: Resultsmentioning

confidence: 99%

Limitation and extrapolation correction of the GGA + U formalism: a case study of Nb-doped anatase TiO2

et al. 2013

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It is rather difficult to model the electronic properties of wide-gap oxides with moderate electronic correlation using first principles methods in the framework of the density functional theory (DFT) together with the Hubbard correction to account for the nonlocal effect in the exchange-correlation (XC) functionals. In this contribution we present a case study of the Nb-doped anatase TiO 2 , to demonstrate such limitation in the GGA + U formalism. It is found that overcorrection owing to a big effective Hubbard parameter U 0 leads to an erroneous band structure, but an inadequate U 0 value results in significantly undervalued prediction of the energy band gap. Fortunately, such limitation in U 0 correction can be addressed satisfactorily through a physically justifiable extrapolation scheme, with electronic structures thus corrected being in excellent agreement with the experimentally observed transparent conductivity of Nb-doped anatase. High resolution X-ray photoelectron spectroscopy (XPS) offers solid support to the theoretical work that Nb doping lowers the valence band without introduction of gap states, and the measured valency of Nb in TiO 2 is in excellent agreement with the calculated value. Also, the current method has been successfully applied to other well-known and yet electronically rather different TCO systems, the Al-doped ZnO and F-doped SnO 2 .

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XAS investigation of tantalum and niobium in nanostructured TiO2 anatase

Cited by 50 publications

References 22 publications

Novel transparent conducting oxide: Anatase Ti1−xNbxO2

Novel transparent conducting oxide: Anatase Ti1−xNbxO2

The effect of Ta doping in polycrystalline TiOx and the associated thin film transistor properties

Limitation and extrapolation correction of the GGA + U formalism: a case study of Nb-doped anatase TiO2

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