Oxygen vacancy defects in tantalum pentoxide: a density functional study

Ramprasad, Rampi; Sadd, M.; Roberts, Doug; Remmel, T.; Raymond, M.; Luckowski, E.; Kalpat, S.; Barron, Carole; Miller, M.

doi:10.1016/s0167-9317(03)00296-x

Cited by 16 publications

(9 citation statements)

References 10 publications

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“…The optimized Ta 16 O 40 structure was found to have C s molecular symmetry with no dissociation of the Ta–O bond (see Table S1 for the Cartesian coordinates). The Ta–O bond lengths were within the range of 1.899–2.139 Å with an average value of 1.988 Å and thus in good agreement with reported experimental results . The calculation results also suggested that Ta 16 O 40 has electronic properties similar to those of bulk Ta 2 O 5 .…”

Section: Results and Discussionsupporting

confidence: 87%

Effects of Ta₂O₅ Surface Modification by NH₃ on the Electronic Structure of a Ru-Complex/N–Ta₂O₅ Hybrid Photocatalyst for Selective CO₂ Reduction

et al. 2018

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This work examined a Ru-complex/N−Ta 2 O 5 (N−Ta 2 O 5 : nitrogen-doped Ta 2 O 5 ) hybrid photocatalyst for CO 2 reduction. In this material, electrons are transferred from the N−Ta 2 O 5 to the Ru-complex in response to visible light irradiation, after which CO 2 reduction occurs on the complex. N-doping is believed to produce an upward shift in the conduction band minimum (CBM) of the Ta 2 O 5 , thus allowing more efficient electron transfer, although the associated mechanism has not yet been fully understood. In the present study, the effects of NH 3 adsorption (the most likely surface modification following nitrification) were examined using a combined experimental and theoretical approach. X-ray photoelectron spectroscopy data suggest that NH 3 molecules are adsorbed on the N−Ta 2 O 5 surface, and it is also evident that the photocatalytic activity of the Ru-complex/N−Ta 2 O 5 is decreased by the removal of this adsorbed NH 3 . Calculations show that both the occupied and unoccupied orbital levels of Ta 16 O 40 (NH 3 ) x clusters (x = 4, 8, 12, or 16) are shifted upward as x is increased. Theoretical analyses of Ru-complex/cluster hybrids demonstrate that the gap between the lowest unoccupied molecular orbital of the Ta 16 O 40 moiety and the unoccupied orbitals of the Ru-complex in Rucomplex/Ta 16 O 40 (NH 3 ) 12 is much smaller than that in Ru-complex/Ta 16 O 40 . The highest occupied molecular orbital of [Rucomplex/Ta 16 O 40 ] − is evidently localized on the Ta 16 O 40 moiety, whereas that of [Ru-complex/Ta 16 O 40 (NH 3 ) 12 ] − is spread over both the Ta 16 O 40 and Ru-complex. These results indicate that the NH 3 adsorption associated with N-doping can result in an upward shift of the CBM of Ta 2 O 5 . Additional calculations for Ta 16 O 40−y (NH) y (y = 2, 4, 6, 8, or 10) suggest that the substitution of NH groups for oxygen atoms on the Ta 2 O 5 surface may be responsible for the red shift in the adsorption band edge of the oxide but makes only a minor contribution to the upward shift of the CBM.

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Section: Results and Discussionsupporting

confidence: 87%

Effects of Ta₂O₅ Surface Modification by NH₃ on the Electronic Structure of a Ru-Complex/N–Ta₂O₅ Hybrid Photocatalyst for Selective CO₂ Reduction

et al. 2018

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“…Thus, the before-mentioned EPR investigations of the powders synthesized by microwave-assisted precursor decomposition proved the existence of different types of oxygen vacancies on the surface of Ta 2 O 5 , which have hitherto only been reported in a few theoretical studies. [47][48][49][50] This is in accordance with photoluminescence studies reported here ( Fig. 7) and by other groups revealing multiple defect energy states in the band gap.…”

Section: Dielectric Propertiessupporting

confidence: 93%

“…46 According to first-principles calculations, various types of oxygen vacancies were predicted, which correspond to sites with different coordination spheres in the Ta 2 O 5 lattice. 47,48 The differences in the g-factors and linewidths from as-received to annealed samples indicate different site symmetries and locations of defect centres, which can be attributed naturally to oxygen vacancies.…”

Section: Epr Studiesmentioning

confidence: 99%

A microwave molecular solution based approach towards high-κ-tantalum(v)oxide nanoparticles: synthesis, dielectric properties and electron paramagnetic resonance spectroscopic studies of their defect chemistry

Hoffmann

Kaloumenos

Spiehl

et al. 2015

Phys. Chem. Chem. Phys.

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Stable dispersions of tantalum oxide nanoparticles are accessible from solutions of tantalum(V) complexes with a mixed malonato and alkanolato ligand sphere in ethoxyethanol by microwave processing. The malonato ligand is cleaved during decomposition and acetic acid or acetic acid esters are formed as derived from in situ spectroscopic studies. The solubility of the tantalum precursor and the obtained particle size therefrom depend strongly on the type of alkanolato ligand moiety. Dispersions of the molecular complexes possess good film forming properties. Films with low surface roughness can be obtained by spincoating. These exhibited a dielectric constant of about 15 and disruptive strengths above 1.5 MV cm(-1). The electrical measurements indicate that the presence of moisture is detrimental with respect to the dielectric performance of the films. After removal of the solvent from the suspensions of the nanoparticles, the residue can be redispersed in aprotic solvents. The particles can be isolated therefrom by precipitation with pentane. XRD and HRTEM indicate that the material remains amorphous up to temperatures of 750 °C. XPS proved that only Ta2O5 is formed as lower oxidation states of Ta cannot be detected. A detailed EPR study allows us to gain insight into the surface defect chemistry. Multiple types of oxygen vacancies exist at the surface of the Ta2O5 particles which are influenced by additional calcination and annealing in a vacuum.

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“…These O atoms build up a plane which will be referred as O plane. It is not easy to calculate the electronic structure of a crystal with such a big unit cell and usually simplified models of Ta 2 O 5 structure were used in the calculations [30,31]. A geometry optimized Ta 6 O 15 unit cell was used in Ref.…”

Section: Electronic Structure Revealed By Dft Calculationmentioning

confidence: 99%

“…[30] to simulate the non-defect containing electronic structure. Simplified Ta 4 O 10 unit cell was also used [31]. These simplified unit cells keep the local environment of Ta atoms close to that of the real unit cell where Ta atoms has five or four neighboring O atoms in the Ta-O planes.…”

Section: Electronic Structure Revealed By Dft Calculationmentioning

confidence: 99%

Electronic structure and charge transport properties of amorphous Ta2O5 films

Швец

Алиев

Gritsenko

et al. 2008

Journal of Non-Crystalline Solids

119

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Oxygen vacancy defects in tantalum pentoxide: a density functional study

Cited by 16 publications

References 10 publications

Effects of Ta₂O₅ Surface Modification by NH₃ on the Electronic Structure of a Ru-Complex/N–Ta₂O₅ Hybrid Photocatalyst for Selective CO₂ Reduction

Effects of Ta₂O₅ Surface Modification by NH₃ on the Electronic Structure of a Ru-Complex/N–Ta₂O₅ Hybrid Photocatalyst for Selective CO₂ Reduction

A microwave molecular solution based approach towards high-κ-tantalum(v)oxide nanoparticles: synthesis, dielectric properties and electron paramagnetic resonance spectroscopic studies of their defect chemistry

Electronic structure and charge transport properties of amorphous Ta2O5 films

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Oxygen vacancy defects in tantalum pentoxide: a density functional study

Cited by 16 publications

References 10 publications

Effects of Ta2O5 Surface Modification by NH3 on the Electronic Structure of a Ru-Complex/N–Ta2O5 Hybrid Photocatalyst for Selective CO2 Reduction

Effects of Ta2O5 Surface Modification by NH3 on the Electronic Structure of a Ru-Complex/N–Ta2O5 Hybrid Photocatalyst for Selective CO2 Reduction

A microwave molecular solution based approach towards high-κ-tantalum(v)oxide nanoparticles: synthesis, dielectric properties and electron paramagnetic resonance spectroscopic studies of their defect chemistry

Electronic structure and charge transport properties of amorphous Ta2O5 films

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Effects of Ta₂O₅ Surface Modification by NH₃ on the Electronic Structure of a Ru-Complex/N–Ta₂O₅ Hybrid Photocatalyst for Selective CO₂ Reduction

Effects of Ta₂O₅ Surface Modification by NH₃ on the Electronic Structure of a Ru-Complex/N–Ta₂O₅ Hybrid Photocatalyst for Selective CO₂ Reduction