Lowering insulator-to-metal transition temperature of vanadium dioxide thin films via co-sputtering, furnace oxidation, and thermal annealing
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Vishwa Krishna Rajan↗
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Results for “vanadium oxide”
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High-Field Nuclear Magnetic Resonance (NMR) Spectroscopy
Nuclear magnetic resonance (NMR) is a non-destructive spectroscopic technique that provides detailed molecular structural information via the electronic environments of nuclei in materials. Higher magnetic field strengths enhance the resolution of NMR, enabling discernment of unique chemical environments that might not be possible at low fields. Herein, the application of high-field NMR to catalyst and electrochemical system characterization are detailed. A brief description of NMR and quadrupolar nuclei are presented where the effects of magnetic field are described. Examples of high-field NMR are provided with particular focus on employing NMR to elucidate the structure of oxides of aluminum and vanadium for catalyst applications. The role of high-field NMR to conduct challenging experiments for energy storage materials is also explored and numerous other nuclei which require high-field measurement are briefly summarized.
Catalyst, Spectroscopy, NMR, High-field, Quadrupol↗
Vanadium Valence in MgAl2O4 Spinels at Reducing Conditions (IW to IW-5)
Vanadium is commonly a major or minor element in spinel structured oxides from a wide range of planetary materials [1-3]. Vanadium is stable in multiple valence states of 5+, 4+, 3+, and 2+ in natural systems, and spinel-structured oxides are known to host vanadium in 4+, 3+, and 2+ [4-6]. However, the understanding of 2+ stability at lower fO2 conditions has been hindered by lack of experiments at or below IW-1 conditions [5]. Insufficient experimental data is available due to the difficulty in controlling fO2 at low conditions in general, and the lack of appropriate standards for comparison to natural materials. Our progress on controlling fO2 in high pressure experimental samples has allowed us to create reducing conditions that are appropriate to studying V valence in spinels at fO2 relevant to natural reducing systems [7]. Here we extend this approach to study V in reduced conditions, at high temperatures. After at-tempting shorter durations and lower temperatures, we demonstrated the need for equilibration times > 6 hours at 1600 °C in order to approach equilibrium. Only then can we produce highly equilibrated samples that provide new insights into V valence at low fO2.
oxygen fugacity↗
Mechanism of superhyperfine structure in sno sub 2-v super 4 plus.
Mechanism of superhyperfine structure inferred from large and small SHFS observed in electron spin resonance spectrum of vanadium ion doped tin oxide
TIN OXIDE↗
Development of Biological and Electrochemical Technologies for the Clean Extraction of Copper and Critical Materials from Low Grade Ores
As we transition toward renewable energy resources and electrification, there will be an increasing demand for critical materials, including copper. While copper is currently mined in the US, processing capacity is not sufficient, and intermediate mining products are shipped to Asia for further processing. The goal of this research was to develop a transformative hydrometallurgical process for the production of copper from low-grade ores that would eliminate the need for smelting and would increase the domestic processing capacity in the US, The project initially focused on the electrochemical reduction of copper concentrate using vanadium, followed by the biological oxidation to produce a stream compatible with existing solvent extraction and electrowinning operations. We discovered an efficient electrochemical process that could produce copper salts from concentrate without the need for biological oxidation, and this technology has been licensed and spun-off into a start-up company. The microbes involved in the current state-of-the-art bioleaching processes were genetically modified to introduced a number of new traits, including increased sulfur oxidation, salt-tolerance, and binding of other critical metals such as cobalt, molybdenum, rhenium, and the rare earth elements. The project was extended to also explore the electrochemical oxidation of copper concentrate using cerium which would potentially eliminate production of hydrogen sulfide that occurs with the reductive leaching process. This technology was found to have slower kinetics, however could it still be developed as an alternative process for domestic copper production and has been found to be applicable to other critical minerals.
42 ENGINEERING↗
Metallic oxide switches using thick film technology
Metallic oxide thick film switches were processed on alumina substrates using thick film technology. Vanadium pentoxide in powder form was mixed with other oxides e.g., barium, strontium copper and glass frit, ground to a fine powder. Pastes and screen printable inks were made using commercial conductive vehicles and appropriate thinners. Some switching devices were processed by conventional screen printing and firing of the inks and commercial cermet conductor terminals on 96% alumina substrates while others were made by applying small beads or dots of the pastes between platinum wires. Static, and dynamic volt-ampere, and pulse tests indicate that the switching and self-oscillatory characteristics of these devices could make them useful in memory element, oscillator, and automatic control applications.
Patel, D. N.↗
Ceramic oxide reactions with V2O5 and SO3
Ceramic oxides are not inert in combustion environments, but can react with, inter alia, SO3, and Na2SO4 to yield low melting mixed sulfate eutectics, and with vanadium compounds to produce vanadates. Assuming ceramic degradation to become severe only when molten phases are generated in the surface salt (as found for metallic hot corrosion), the reactivity of ceramic oxides can be quantified by determining the SO3 partial pressure necessary for molten mixed sulfate formation with Na2SO3. Vanadium pentoxide is an acidic oxide that reacts with Na2O, SO3, and the different ceramic oxides in a series of Lux-Flood type of acid-base displacement reactions. To elucidate the various possible vanadium compound-ceramic oxide interactions, a study was made of the reactions of a matrix involving, on the one axis, ceramix oxides of increasing acidity, and on the other axis, vanadium compounds of increasing acidity. Resistance to vanadium compound reaction increased as the oxide acidity increased. Oxides more acidic than ZrO2 displaced V2O5. Examination of Y2O3- and CeO2-stabilized ZrO2 sintered ceramics which were degraded in 700 C NaVO3 has shown good agreement with the reactions predicted above, except that the CeO2-ZrO2 ceramic appears to be inexplicably degraded by NaVO3.
Jones, R. L.↗
Integrated Experimental and Computational K-Edge X-ray Absorption Near-Edge Structure Analysis of Vanadium Catalysts
X-ray Absorption Near-Edge Structure (XANES) spectroscopy is a powerful tool to reveal key structural and electronic features of isolated catalytic sites, yet insights into molecular structure and more detailed orbital analysis through a combination of experimental and computed XANES analysis are necessary for accurate interpretation of the spectra, especially when significant heterogeneity exits among the catalytic sites. Herein, we present an integrated computational and experimental strategy to determine both primary and secondary bonding interactions within the XANES pre-edge region for organovanadium complexes, which was developed using a series of well-defined molecular vanadium complexes and then applied to the characterization of a supported organovanadium olefin hydrogenation catalyst. Time-dependent density functional theory is used to predict the energy of pre-edge XANES features for a series of vanadium complexes with a variety of oxidation states and local coordination environments. Further, a calibration scheme incorporating different density functionals and basis sets is established, resulting in an optimized scheme that accurately predicts pre-edge energies with a mean absolute error of 0.40 eV. Second-shell coordination (e.g., V---V) effects within XANES are identified through the analysis of the computed dominant orbital contributions for multi-vanadium complexes. Orbital analysis also provided confirmation that the vanadium-hydride formation combined with the heterogeneity of the catalytic active species in ole-fin hydrogenation caused the energy shift and broadening of the pre-edge peak after hydrogen treatment of the silica-supported organovanadium pre-catalyst. This work further elucidates computational XANES simulations and techniques potentially guiding characterization in surface organometallic chemistry.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Enhanced Catalytic Performance of a Ce/V Oxo Cluster through Confinement in Mesoporous SBA-15
To increase catalytic efficiency, mesoporous supports have been widely applied to immobilize well-defined metal oxide clusters due to their ability to stabilize highly dispersed clusters. Here, for this study, a redox-active heterometallic Ce 12 V 6 -oxo cluster (CeV) was first presynthesized and then incorporated into mesoporous silica, SBA-15, via a straightforward impregnation method. Scanning transmission electron microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR), in concert with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), verified the successful introduction of the CeV cluster inside the pore of SBA-15. The 51 V magic angle spinning solid-state nuclear magnetic resonance ( 51 V MAS NMR) spectroscopy and differential pair distribution function (dPDF) analysis confirmed the structural integrity of the CeV cluster inside the SBA-15. The composite was then benchmarked for liquid-phase oxidation of 2-chloroethyl ethyl sulfide (CEES) under mild conditions and gas-phase oxidative dehydrogenation (ODH) of propane under high temperatures (up to 550 °C). The catalytic reactivity results demonstrated 8- and 14-fold increase in turnover frequency (TOF) values of the composite (CeV@10SBA-2) than the bulk CeV cluster under the same conditions for CEES oxidation and ODH, respectively. These results highlight the improved reactivity of the catalytically active CeV cluster as attributed to the higher dispersion of the discrete cluster upon immobilization within the SBA-15 support.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Oxidation mechanism in a refractory multiple-principal-element alloy at high temperature
Refractory multiple-principal-element alloys (RMPEAs) are promising structural materials to enable increased power efficiency in high-temperature oxidation environments, but the oxidation behavior and microstructures of the oxides, especially at the beginning of the oxidation, have received limited attention. Here, the oxidation mechanism in an equimolar W-Mo-Ta-Nb-V was investigated at 1300 °C and compared with the equimolar W-Mo-Ta-Nb alloy without V. The oxide scale on WMoTaNbV after 1 min exposure is shown to be composed of a degradation layer at the interface of the alloy/oxide, an initial oxide transition layer, followed by the main phase aggregate oxide layer, and an outermost oxide layer. At the early stage of oxidation, the absorption of oxygen by the RMPEA substrate forms a solid solution. Vanadium accelerates the initial degradation process as it forms VO. The initial oxidation-induced degradation of RMPEA follows a sequence governed by the free energy change accompanied by local element segregation. Liquid V-Mo oxides aggregate in the intermediate oxide layer. The inward growth of the oxide scale is controlled by the local composition changes, the orientation of the substrate, the crystal structure, and physical properties such as melting points of the oxides.
36 MATERIALS SCIENCE↗
Tuning effect of vanadium substitution on the structural and electronic properties of potassium hollandite surfaces
Metal oxide surfaces possess unique properties that are crucial for a wide variety of applications. Herein, density functional theory calculations are performed to study surfaces of potassium hollandite, KMn 8 O 16 , a promising cathode material for electrochemical energy storage, and the vanadium-substituted analog KMn 7 VO 16 . The results show that there is a clear increase in the stability of KMn 8 O 16 with (001) < (110) < (100) or (010), apt to adopt an elongated rod-like morphology. The vanadium (V)-substitution lowers the crystal symmetry and prefers to occupy the surface sites, resulting in electron redistribution and selective tuning of surface energy depending on the surface structures. In particular, the higher stability of substituted V 4+ compared with Mn 4+ ions leads to stabilization of the (001) surface due to the direct interaction of reduced Mn δ+ ions on the surface, while such tuning effect decreases with the increase in surface stability, (110) > (100) and (010). As a result, the KMnO 16 rod is shortened upon V-substitution as observed experimentally, effectively facilitating the ion transport during discharge. The V substituents also introduce stabilization to the defect surfaces resulting from Mn 2+ dissolution during cycling, thereby hindering further structural decay. In conclusion, our study demonstrates the potential tuning effect of V-substitution to promote the ion transport and mitigate the capacity degradation of α-MnO 2 -based materials.
25 ENERGY STORAGE↗
Photon Activation Analysis in Gallium, Nickel, and Vanadium
Here this research explored the development of the photonuclear production method of 67 Cu from 71 Ga as well as 47 Sc from 51 V. Both products serve as high-demand research medical radioisotopes. Furthermore, an understanding of these reactions is significant to fundamental nuclear physics and astrophysics. Bremsstrahlung flux was induced by an electron linac and a 1-mm tungsten radiator. Irradiation of gallium oxide powder, 98.78% pure 71 Ga, and a natural vanadium foil at 30.9 MeV and 100 W for 1 h produced 64.4 ± 0.4 Bq/W·s·kg of 67 Cu and 164 ± 3.1 Bq/W·s·kg of 47 Sc. A secondary irradiation with 99.6% pure 71 Ga and natural vanadium at 31.5 MeV and 100 W for 1.1 h produced 79.8 ± 0.9 Bq/W·s·kg of 67 Cu and 136 ± 7.2 Bq/W·s·kg of 47 Sc. The photoinduced activation is promising; however, further research into optimal geometry and power is required to maximize specific activity. Natural nickel was also irradiated to serve as a benchmark comparison. Effective cross sections for each reaction were inferred.
47Sc↗
Shifts in valence states in bimetallic MXenes revealed by electron energy-loss spectroscopy (EELS)
MXenes are an emergent class of two-dimensional materials with a very wide spectrum of promising applications. The synthesis of multiple MXenes, specifically solid-solution MXenes, allows fine tuning of their properties, expands their range of applications, and leads to enhanced performance. The functionality of solid-solution MXenes is closely related to the valence state of their constituents: transition metals, oxygen, carbon, and nitrogen. However, the impact of changes in the oxidation state of elements in MXenes is not well understood. In this work, three interrelated solid-solution MXene systems (Ti$_{2–y}$Nb$_y$CT$_x$, Nb$_{2–y}$V$_y$CT$_x$, and Ti$_{2–y}$V$_y$CT$_x$) were investigated with scanning transmission electron microscopy and electron energy-loss spectroscopy to determine the localized valence states of metals at the nanoscale. The analysis demonstrates changes in the electronic configuration of V upon modification of the overall composition and within individual MXene flakes. These shifts of oxidation state can explain the nonlinear optical and electronic features of solid-solution MXenes. Vanadium appears to be particularly sensitive to modification of the valence state, while titanium maintains the same oxidation state in Ti–Nb and Ti–V MXenes, regardless of stoichiometry. Here, the study also explains Nb's influential role in the previously observed electronic properties in the Nb–V and Nb–Ti systems.
36 MATERIALS SCIENCE↗
The high-valent vanadium chemistry of isoindoline chelates
Isoindoline-based chelates, in particular bis(arylimino)isoindolines, have shown extensive metal binding chemistry. Although this chemistry has been explored for the middle and late transition metal ions, little work has been carried out on early transition metal complexes. In this article, we present the first examples of vanadium coordinated using four bis(arylimino)isoindolines, in which the aryl groups are pyrazole, indazole, benzimidazole, and pyridine (ligands 1–4 , respectively). We isolated five complexes using vanadyl sulfate or vanadyl acetylacetonate as the vanadium source. In all cases, the ligands bound in a meridional mode, and for four of the complexes, the vanadium ion was observed in the V(v) oxidation state. Three of the ligands ( 1–3 ) formed VO 2 complexes with vanadyl sulfate and vanadyl acetylacetonate, but the bis(pyridylimino)isoindoline (ligand 4 ) formed a V(v) oxosulfonato complex with the former starting material and a vanadyl V(iv) acetylacetonate with the latter starting material. All metal compounds were structurally elucidated by X-ray crystallographic methods, and we probed their electronic structures using DFT methods.
Bore, Joan C. [Univ. of Akron, OH (United States)]↗
Lunar and Planetary Science XXXV: Special Session: Oxygen in the Solar System, II
The Special Session: Oxygen in the Solar System, II, included the following reports:Evolution of Oxygen Isotopes in the Solar Nebula; Disequilibrium Melting of Refractory Inclusions: A Mechanism for High-Temperature Oxygen; Isotope Exchange in the Solar Nebula; Oxygen Isotopic Compositions of the Al-rich Chondrules in the CR Carbonaceous Chondrites: Evidence for a Genetic Link to Ca-Al-rich Inclusions and for Oxygen Isotope Exchange During Chondrule Melting; Nebular Formation of Fayalitic Olivine: Ineffectiveness of Dust Enrichment; Water in Terrestrial Planets: Always an Oxidant?; Oxygen Barometry of Basaltic Glasses Based on Vanadium Valence Determination Using Synchrotron MicroXANES; A New Oxygen Barometer for Solar System Basaltic Glasses Based on Vanadium Valence; The Relationship Between Clinopyroxene Fe3+ Content and Oxygen Fugacity ; and Olivine-Silicate Melt Partitioning of Iridium.
Source record↗
Hydrophobic Catalysts For Removal Of NOx From Flue Gases
Improved catalysts for removal of nitrogen oxides (NO and NO2) from combustion flue gases formulated as composites of vanadium pentoxide in carbon molecular sieves. Promotes highly efficient selective catalytic reduction of NOx at relatively low temperatures while not being adversely affected by presence of water vapor and sulfur oxide gases in flue gas. Apparatus utilizing catalyst of this type easily integrated into exhaust stream of power plant to remove nitrogen oxides, generated in combustion of fossil fuels and contribute to formation of acid rain and photochemical smog.
Sharma, Pramod K.↗
Tunable 3D Aerosol Jet Printing of Low‐Power Redox‐Gated Transistors with Multicomponent Inks
Printed hybrid electronics (PHE) offer a promising alternative for microelectronics fabrication, addressing some limitations of traditional subtractive manufacturing. Despite the versatility of PHE, particularly in the customization of printing inks, these devices have not yet matched the performance of silicon-based electronics due to challenges in gating mechanisms and operational stability. However, the potential of low-voltage redox-gating to achieve significant carrier modulations in correlated metal oxides remains unexplored in PHE. This study systematically investigates vanadium dioxide (VO 2 ) nanoparticles and redox inks, linking their organization in solution to their morphology, phase state, and properties in solid films and multilayered structures. Using an aerosol jet printer (AJP), a solid-state VO 2 transistor is fabricated, operating at just 0.4 V gating voltage. The printed VO 2 films demonstrate redox-modulated conductivity and consistent transistor behavior. The solid-state redox gating materials also provide long-term stability, with the device maintaining performance over 6000 cycles without degradation. These results highlight the potential of redox gating to enhance the application of functional nanoparticles in printed hybrid microelectronics, especially for flexible, low-voltage, and energy-efficient devices.
36 MATERIALS SCIENCE↗
Wide bandgap photoconductor (SiC:V)-based optically addressed light valve for high fluence operation
Optically addressable light valves based on wide bandgap 4H- and 6H-SiC as photoconductors were designed to withstand higher operational laser fluences than the state of-the-art bismuth silicon oxide (BSO; Bi 12 SiO 20 ) based devices. Vanadium-doped SiC was selected as the photoconductors due to their reasonable photoresponsivity while many fold improvement in laser induced damage threshold as compared to BSO. The laser induced damage threshold values of the materials were measured after exposing ~ 200 sites on the samples to increasing levels of fluence of a gaussian pulsed Nd: YAG laser system (1064 nm) with a 5 Hz repetition rate. The measured damage threshold values for BSO, 4H- and 6H-SiC were 0.4 J/cm 2 , 1.75 J/cm 2 and 1.8 J/cm 2 , respectively. Photoconductive switches based on 4H and 6H-SiC samples were characterized at wavelengths of 380 nm, 405 nm, and 447 nm. The peak photoresponsivity values of the 4H- and 6H-SiC materials were measured to be under 380 nm and 405 nm, respectively. The photoconductor was bonded to a BK7 optical window with 5 μm diameter microspheres as spacers. A twisted nematic type E7 liquid crystal (LC) was filled in the 5 μm gap in a vacuum chamber. The desired alignment of the liquid crystal was achieved by mutually orthogonal orientation of LC alignment layers on the two mating faces (SiC and BK7). The fabricated devices were modulated using address beams of wavelengths 380 nm, 405 nm, and 447 nm. In conclusion, required transmission levels of > 90% was achieved for the fabricated OALVs for a sinusoidal voltage waveform that meets the lifetime requirement of the device.
36 MATERIALS SCIENCE↗