scholarly journals Role of Oxygen Vacancies in the Electrical Properties of WO3−x Nano/Microrods with Identical Morphology

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Zhenguang Shen ◽  
Zengying Zhao ◽  
Jian Wen ◽  
Jingwen Qian ◽  
Zhijian Peng ◽  
...  
Keyword(s):  
Oxygen Vacancies ◽  
Solar Irradiation ◽  
Strong Response ◽  
Fixed Amount ◽  
Resistance Response ◽  
Ceramic Substrates ◽  
Tungsten Oxides ◽  
Interdigital Electrodes ◽  
Ceramic Boat ◽  
Reductive Atmosphere

Tungsten oxide (WO3−x) crystalline nano/microrods with identical morphology but different contents of oxygen vacancies were prepared by thermally evaporating fixed amount of WO3 powder in reductive atmosphere from different amounts of S power at 1150°C in a vacuum tube furnace, in which both sources were loaded in separate ceramic boat. With increasing amount of S powder, a series of tungsten oxides, WO3, WO2.90, W19O55 (WO2.89), and W18O49 (WO2.72), could be obtained. And devices were fabricated by screen-printing the obtained WO3−x crystals on ceramic substrates with Ag-Pd interdigital electrodes. With increasing content of oxygen vacancies, the devices fabricated with WO3−x crystals present a negative to positive resistance response to relative humidity. Under dry atmosphere, for the devices with increasing x, the strong response to light changed from short to long wavelength; under light irradiation, the conducting ability of the devices was enhanced, due to the more efficient separation and transportation of the photogenerated carriers; and under simulated solar irradiation, the photocurrent intensity of the W18O49 device was roughly 8 times, about 500 times, and even 1000 times larger than that of the W19O55, WO2.90, and WO3 one, respectively. With the versatile optoelectrochemical properties, the obtained WO3−x crystals have the great potential to prepare various humidity sensors and optoelectrical devices.

Contributions of oxygen vacancies to the hydrogen evolution catalytic activity of tungsten oxides

2021 ◽  
Vol 46 (1) ◽  
pp. 676-682
Author(s):  
Jiajia Lu ◽  
Guangfu Qian ◽  
Lin Luo ◽  
Huibing He ◽  
Shibin Yin
Keyword(s):  
Catalytic Activity ◽  
Hydrogen Evolution ◽  
Oxygen Vacancies ◽  
Tungsten Oxides

scholarly journals Direct observation of oxygen-vacancy formation and structural changes in Bi2WO6 nanoflakes induced by electron irradiation

2019 ◽  
Vol 10 ◽  
pp. 1434-1442 ◽  
Author(s):  
Hong-long Shi ◽  
Bin Zou ◽  
Zi-an Li ◽  
Min-ting Luo ◽  
Wen-zhong Wang
Keyword(s):  
Electron Irradiation ◽  
Oxygen Vacancies ◽  
Structural Changes ◽  
Cluster Formation ◽  
Energetic Electron ◽  
Structural Evolution ◽  
Formation Mechanisms ◽  
Tungsten Oxides ◽  
Transmission Electron ◽  
Oxygen Vacancy Formation

The prominent role of oxygen vacancies in the photocatalytic performance of bismuth tungsten oxides is well recognized, while the underlying formation mechanisms remain poorly understood. Here, we use the transmission electron microscopy to investigate the formation of oxygen vacancies and the structural evolution of Bi2WO6 under in situ electron irradiation. Our experimental results reveal that under 200 keV electron irradiation, the breaking of relatively weak Bi–O bonds leads to the formation of oxygen vacancies in Bi2WO6. With prolonged electron irradiation, the reduced Bi cations tend to form Bi clusters on the nanoflake surfaces, and the oxygen atoms are released from the nanoflakes, while the W–O networks reconstruct to form WO3. A possible mechanism that accounts for the observed processes of Bi cluster formation and oxygen release under energetic electron irradiation is also discussed.

scholarly journals Femtosecond visualization of oxygen vacancies in metal oxides

2020 ◽  
Vol 6 (10) ◽  
pp. eaax9427 ◽  
Author(s):  
Xinping Zhang ◽  
Fawei Tang ◽  
Meng Wang ◽  
Wangbin Zhan ◽  
Huaxin Hu ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Oxygen Vacancy ◽  
Metal Oxides ◽  
Oxygen Vacancies ◽  
Time Resolved ◽  
Tungsten Oxides ◽  
Structure Of Metal ◽  
Evolution Dynamics ◽  
Spatial Locations

Oxygen vacancies often determine the electronic structure of metal oxides, but existing techniques cannot distinguish the oxygen-vacancy sites in the crystal structure. We report here that time-resolved optical spectroscopy can solve this challenge and determine the spatial locations of oxygen vacancies. Using tungsten oxides as examples, we identified the true oxygen-vacancy sites in WO2.9 and WO2.72, typical derivatives of WO3 and determined their fingerprint optoelectronic features. We find that a metastable band with a three-stage evolution dynamics of the excited states is present in WO2.9 but is absent in WO2.72. By comparison with model bandstructure calculations, this enables determination of the most closely neighbored oxygen-vacancy pairs in the crystal structure of WO2.72, for which two oxygen vacancies are ortho-positioned to a single W atom as a sole configuration among all O─W bonds. These findings verify the existence of preference rules of oxygen vacancies in metal oxides.

Conditions for atomic imaging of mullite

1989 ◽  
Vol 47 ◽  
pp. 418-419
Author(s):  
T. A. Epicier ◽  
G. Thomas
Keyword(s):  
Oxygen Vacancies ◽  
High Resolution Electron Microscopy ◽  
Ceramic Materials ◽  
Work Conditions ◽  
Real Space ◽  
Potential Candidate ◽  
Silicate Mineral ◽  
Resolution Electron ◽  
The Subject ◽  
Aluminium Silicate

Mullite is an aluminium-silicate mineral of current interest since it is a potential candidate for high temperature applications in the ceramic materials field.In the present work, conditions under which the structure of mullite can be optimally imaged by means of High Resolution Electron Microscopy (HREM) have been investigated. Special reference is made to the Atomic Resolution Microscope at Berkeley which allows real space information up to ≈ 0.17 nm to be directly transferred; numerous multislice calculations (conducted with the CEMPAS programs) as well as extensive experimental through-focus series taken from a commercial “3:2” mullite at 800 kV clearly show that a resolution of at least 0.19 nm is required if one wants to get a straightforward confirmation of atomic models of mullite, which is known to undergo non-stoichiometry associated with the presence of oxygen vacancies.Indeed the composition of mullite ranges from approximatively 3Al2O3-2SiO2 (referred here as 3:2-mullite) to 2Al2O3-1SiO2, and its structure is still the subject of refinements (see, for example, refs. 4, 5, 6).

Comparison of the Non-Specific Binding of Unfractionated Heparin and Low Molecular Weight Heparin (Enoxaparin) to Plasma Proteins

1993 ◽  
Vol 70 (04) ◽  
pp. 625-630 ◽  
Author(s):  
Edward Young ◽  
Benilde Cosmi ◽  
Jeffrey Weitz ◽  
Jack Hirsh
Keyword(s):  
Molecular Weight ◽  
Unfractionated Heparin ◽  
Plasma Proteins ◽  
Low Molecular Weight Heparin ◽  
Specific Binding ◽  
Anticoagulant Activity ◽  
Factor Xa ◽  
Low Molecular Weight ◽  
Heparin Binding ◽  
Fixed Amount

SummaryThe non-specific binding of anticoagulantly-active heparin to plasma proteins may influence its anticoagulant effect. We used low affinity heparin (LAH) essentially devoid of anti-factor Xa activity to investigate the extent and possible mechanism of this non-specific binding. The addition of excess LAH to platelet-poor plasma containing a fixed amount of unfractionated heparin doubled the anti-factor Xa activity presumably because it displaces anticoagulantly-active heparin from plasma proteins. Although dextran sulfates of varying molecular weights also increased the anti-factor Xa activity, less sulfated heparin-like polysaccharides had no effect. These findings suggest that the ability to displace active heparin from plasma protein binding sites is related to charge and may be independent of molecular size. In contrast to its effect in plasma containing unfractionated heparin, there was little augmentation in anti-factor Xa activity when LAH was added to plasma containing low molecular weight heparin (LMWH), indicating that LMWH binds less to plasma proteins than unfractionated heparin. This concept is supported by studies comparing the anticoagulant activity of unfractionated heparin and LMWH in plasma with that in buffer containing antithrombin III. The anti-factor Xa activity of unfractionated heparin was 2-fold less in plasma than in the purified system. In contrast, LMWH had identical anti-factor Xa activity in both plasma and buffer, respectively. These findings may be clinically relevant because the recovered anti-factor Xa activity of unfractionated heparin was 33% lower in plasma from patients with suspected venous thrombosis than in plasma from healthy volunteers. The reduced heparin recovery in patient plasma reflects increased heparin binding to plasma proteins because the addition of LAH augmented the anti-factor Xa activity. In contrast to unfractionated heparin, there was complete recovery of LMWH added to patient plasma and little increase of anti-factor Xa activity after the addition of LAH. These findings may explain why LMWH gives a more predictable dose response than unfractionated heparin.

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