The role of surface reduction in the formation of Ti interstitials

Gaberle, Julian; Shluger, Alexander L.

doi:10.1039/c9ra01015g

Cited by 7 publications

(6 citation statements)

References 68 publications

(90 reference statements)

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“…11 In a recent DFT-based publication, the energetic barrier for the movement of Ti 3+ interstitials was reported to be 2.5−3.0 eV, which suits our assumption very well. 17 Also, a local high density of Ti 3+ might further lower the energy barriers for Ti 3+ diffusion by Coulombic repulsion. However, this effect is probably of minor importance, as revealed by earlier reports on bare ion-sputtered surfaces.…”

Section: Discussionmentioning

confidence: 99%

“…Besides others, titanium dioxide is the most popular representative of such studies, often rutile as its thermodynamically most stable modification . In the last decades, the importance of point defects, particularly oxygen vacancies as the most important surface defect and Ti 3+ interstitials as the dominant bulk defect, turned out to be crucial for the adsorption and reactivity of several molecules. − In single-crystal surfaces, these defects can be introduced by repeated cycles of extended argon-ion bombardment and subsequent annealing at temperatures above 800 K. − Especially the Ti 3+ interstitials, which become mobile at temperatures above 450–500 K, are often underestimated, also because Ti 3+ charge localization and diffusion are challenging to be included in theoretical studies. − However, it is noteworthy that both point defects are practically carriers of electronic charge, implying a well-controllable self-n-doping with increasing reduction degree. In addition, numerous publications reported the combination of TiO 2 with other transition-metal oxides for the use in catalytic reactions. − By use of such mixed oxide–oxide cocatalysts, several challenges can be addressed, for example, the Lewis acidity, chemical and physical stability, or the size of the band gap and its position, which is crucial for photocatalytic reactions.…”

Section: Introductionmentioning

confidence: 99%

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Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂

2020

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Heterogeneous (photo)catalysts are often complex mixtures of different nanostructured oxidic compounds. Chemical and electronic interactions within such combined materials may play a key role in improving the performance in technological applications but are difficult to investigate under technical conditions. This work presents a systematic study of the interactions between tungsten oxide clusters and the underlying rutile TiO2 (110) surface in special consideration of point defects such as Ti3+ interstitials. Using electron beam evaporation from WO3 powder, stoichiometric (WO3) n , and oxygen-deficient (WO3–x ) n , tungsten oxide clusters are produced simultaneously. Based on cluster coverage- and temperature-dependent X-ray photoelectron spectroscopy studies, the formation of a surface layer of stoichiometric and oxygen-deficient tungsten oxide clusters is shown, and the formation of mixed oxides can be excluded. For the first layer up to 7.1 WO3 nm–2, stoichiometric clusters are dominant at the TiO2 surface. The lack of W5+ indicates an electron transfer from the clusters toward the substrate under formation of Ti3+ interstitials. Furthermore, we found at elevated temperatures relevant for catalytic reactions that the tungsten oxide clusters are more stable on TiO2 surfaces than on other substrates such as the silicon oxide layer of Si wafers. Up to 900 K, only slight changes were observed on titania. We observed an accumulation of Ti3+ at the TiO2 surface between 500 and 800 K in the case of high bulk Ti3+ content in TiO2. As the Ti3+ accumulation is accompanied by significant changes of the W 4f signals, we suggest an interaction between these sites under a possible generation of surface fields or an anionic [(WO3) n ] z−-like cluster by electron transfer from Ti3+.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂

2020

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“…Polarons are another important class of defects that have recently been highlighted and linked to the activity of titania [22][23][24][25], ceria [12] and haematite [10,26]. Polarons are quasiparticles consisting of an electron bound to a lattice distortion, and in a small polaron this coupling is localized to within one or two lattice spacings.…”

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confidence: 99%

Small polarons and the Janus nature of TiO2 (110)

et al. 2020

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Polarons are ubiquitous in many semiconductors and have been linked with conductivity and optical response of materials for photovoltaics and heterogeneous catalysis, yet how surface polarons influence adsorption remains unclear. Here, by modelling the surface of rutile titania using density functional theory, we reveal the effect of small surface polarons on water adsorption, dissociation, and hydrogen bonding. On the one hand the presence of such polarons significantly suppresses dissociation of water molecules that are bonded directly to polaronic sites. On the other hand, polarons facilitate water dissociation at certain non-polaronic sites. Furthermore, polarons strengthen hydrogen bonds, which in turn affects water dissociation in hydrogen bonded overlayer structures.This study reveals that polarons at the rutile surface have complex, multi-faceted, effects on water adsorption, dissociation and hydrogen bonding, highlighting the importance of polarons on water structure and dynamics on such surfaces. We expect that many of the physical properties of surface polarons identified here will apply more generally to surfaces and interfaces that can host small polarons, beyond titania.

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“…The ionization energy of multiple charged ions contributes predominantly to the potential energy in the CAPE process, and the ionization energy is in the range of several electron volts to hundreds of electron volts depending on the charge state of the ion [ 45 ]; note that this ionization energy is much higher than that of the thermal evaporation or magnetron sputtering techniques [ 12 ]. The activation energies for the surface diffusion of the adatoms of Ti and O on the TiO 2 surface are typically ~0.5 eV [ 46 ] and ~2 eV [ 47 ], respectively. These activation energies for the surface diffusion of the adatoms on growing films are smaller than those provided by the ASH in the cathodic arc plasma; this results in enhanced surface mobility during the deposition process.…”

Section: Resultsmentioning

confidence: 99%

Preparation of High-Performance Metal-Free UV/Near Infrared-Shielding Films for Human Skin Protection

Liang¹,

Chen

2021

Nanomaterials

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A series of metal-free UV/near infrared (NIR)-shielding coatings are successfully fabricated by shielded cathodic arc plasma evaporation (CAPE) and substrate-biased RF magnetron sputtering processes. The UV/NIR-shielding coatings comprising quarter-wave stacks of TiO2/SiO2 multilayers and high-conductivity sputter-deposited ITO films with a thickness in the range of 200–600 nm could block IRA and IRB radiations, respectively. The total thicknesses of UV/near infrared-shielding films are in the range from 375 nm to 1513.8 nm. The anatase-phase TiO2 films with absorption edge located at ∼375 nm were deposited by shielded CAPE at ∼100 °C. Further, the well-crystallized ITO films were found to have high free-electron concentrations (1.12 × 1021 cm−3), resulting in strong absorption of IRB due to the plasmon resonance absorption. The optimal optical design and ITO film thickness were investigated, and the TiO2(SiO2/TiO2)3 multilayer combined with an ITO film thickness of 400 nm was found to provide a high NIR-shielding rate of 94.8%, UVB to UVA-shielding rate of 92.7%, and average visible light transmittance of 68.1%. Further, human skin cells protected by a UV/NIR-shielding coating showed significantly decreased reactive oxygen species generation and inflammatory cytokine expression as compared to those of unprotected cells. The results demonstrate that the development of multifunction coatings have potential for transparent heat insulation windows and human skin protection against UV/IR radiations.

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The role of surface reduction in the formation of Ti interstitials

Abstract: Density functional theory simulations are used to investigate the formation and mobility of Ti interstitial ions, Tii, at the (110) surface of rutile TiO2.

Cited by 7 publications

References 68 publications

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂

Small polarons and the Janus nature of TiO2 (110)

Preparation of High-Performance Metal-Free UV/Near Infrared-Shielding Films for Human Skin Protection

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The role of surface reduction in the formation of Ti interstitials

Abstract: Density functional theory simulations are used to investigate the formation and mobility of Ti interstitial ions, Tii, at the (110) surface of rutile TiO2.

Cited by 7 publications

References 68 publications

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti3+ States in Rutile TiO2

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti3+ States in Rutile TiO2

Small polarons and the Janus nature of TiO2 (110)

Preparation of High-Performance Metal-Free UV/Near Infrared-Shielding Films for Human Skin Protection

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Product

Resources

About

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂

Electron Transfer in Oxide–Oxide Cocatalysts: Interaction of Tungsten Oxide Clusters with Ti³⁺ States in Rutile TiO₂