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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Dimensionally Controlled Lithiation of Chromium Oxide

Oxide conversion reactions are an alternative approach for high capacity lithium ion batteries but are known to suffer from structural irreversibility associated with the phase separation and reconstitution of reduced metal species and Li2O. In particular, the morphology of the reduced metal species is thought to play a critical role in the electrochemical properties of a conversion material. Here we use a model electrode with alternating layers of chromium and chromium oxide to better understand and control these phase changes in real-time and at molecular length scales. Despite lacking crystallinity at the atomic scale, this superstructure is observed (with X-ray reflectivity, XR) to lithiate and delithiate in a purely one-dimensional manner, preserving the layered structure. The XR data show that the metal layers act as nucleation sites for the reduction of chromium in the conversion reaction. Irreversibility during delithiation is due to the formation of a ternary phase, LiCrO2, which can be further delithiated at higher potentials. The results reveal that the combination of confining lithiation to nanoscale sheets of Li2O and the availability of reaction sites in the metal layers in the layered structure is a strategy for improving the reversibility and mass transport properties that can be used in a wide range of conversion materials.

25 ENERGY STORAGE↗
DOE OSTI2013

Zinc-oxide charge trapping memory cell with ultra-thin chromium-oxide trapping layer

A functional zinc-oxide based SONOS memory cell with ultra-thin chromium oxide trapping layer was fabricated. A 5 nm CrO{sub 2} layer is deposited between Atomic Layer Deposition (ALD) steps. A threshold voltage (V{sub t}) shift of 2.6V was achieved with a 10V programming voltage. Also for a 2V V{sub t} shift, the memory with CrO{sub 2} layer has a low programming voltage of 7.2V. Moreover, the deep trapping levels in CrO{sub 2} layer allows for additional scaling of the tunnel oxide due to an increase in the retention time. In addition, the structure was simulated using Physics Based TCAD. The results of the simulation fit very well with the experimental results providing an understanding of the charge trapping and tunneling physics.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural, morphological and optical properties of chromium oxide nanoparticles

Chromium oxide nanoparticles are synthesized by reduction route from chloride precursors with surfactant, trioctylphosphine oxide (TOPO). Structural and morphological characterization are analyzed using X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Transmission Electron micrographs show that the average grain size lies in the range 5nm to 10nm. Optical characterization has been done by UV-VIS spectrophotometer. Distinct optical absorptions of Cr{sup 3+} ions show hinting towards the presence of Cr{sub 2}O{sub 3}. Presence of oxygen is also confirmed from Electron Energy Loss Spectroscopy (EELS) studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

The impact of crystal symmetry on the electronic structure and functional properties of complex lanthanum chromium oxides

Complex oxides exhibit a wide range of crystal structures, chemical compositions and physical properties. The underlying drivers determining the complicated structure-composition-property phase diagrams are the relative positions and orbital overlaps between the metal cations and the oxygen anions. Here we report a combined experimental and theoretical investigation of the structure and bonding in a series of lanthanum chromium oxides prepared by reactive molecular beam epitaxy. Of particular interest is the charge state and local coordination of the Cr. We have stabilized LaCrO 3 , LaCrO 4 and La 2 CrO 6 films by controlling the three elemental fluxes during deposition, and have carried out x-ray diffraction, x-ray photoemission, and x-ray absorption spectroscopy, as well as first-principles calculations, to determine structure, charge state, chemical bonding, and electronic structure. Significant changes in bonding character and orbital interaction are revealed with decreasing ligand symmetry from octahedral to tetrahedral Cr coordination. Both LaCrO 4 and LaCrO 6 with tetrahedrally coordinated Cr show strong pre-edge features in the Cr K-edge near-edge structure whereas LaCrO 3 with octahedrally coordinated Cr exhibits very weak pre-edge features. The origin of these pre-edge features is discussed based on various selection rules and ligand symmetry. We also demonstrate an increase in cation-anion orbital hybridization and a decrease in long-range ligand coupling induced by this symmetry reduction. These in turn result in dramatic modifications of the macroscopic optical and magnetic properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Compact chromium oxide thin film resistors for use in nanoscale quantum circuits

We report on the electrical characterisation of a series of thin amorphous chromium oxide (CrO{sub x}) films, grown by dc sputtering, to evaluate their suitability for use as on-chip resistors in nanoelectronics. By increasing the level of oxygen doping, the room-temperature sheet resistance of the CrO{sub x} films was varied from 28 Ω/◻ to 32.6 kΩ/◻. The variation in resistance with cooling to 4.2 K in liquid helium was investigated; the sheet resistance at 4.2 K varied with composition from 65 Ω/◻ to above 20 GΩ/◻. All of the films measured displayed linear current–voltage characteristics at all measured temperatures. For on-chip devices for quantum phase-slip measurements using niobium–silicon nanowires, interfaces between niobium–silicon and chromium oxide are required. We also characterised the contact resistance for one CrO{sub x} composition at an interface with niobium–silicon. We found that a gold intermediate layer is favourable: the specific contact resistivity of chromium-oxide-to-gold interfaces was 0.14 mΩcm{sup 2}, much lower than the value for direct CrO{sub x} to niobium–silicon contact. We conclude that these chromium oxide films are suitable for use in nanoscale circuits as high-value resistors, with resistivity tunable by oxygen content.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Effect of reaction temperature on crystallite size and sensing response of chromium oxide nanoparticles

Graphical abstract: Sensing response towards 250 ppm ethanol for the samples synthesized at different reaction temperatures at different operating temperatures. Highlights: ► Effect of reaction temperature on particle size of Cr{sub 2}O{sub 3}. ► No catalyst has been incorporated to enhance the response of the material. ► Synthesis of Cr{sub 2}O{sub 3} nanoparticles. -- Abstract: Nanoparticles of chromium oxide have been synthesized following a precipitation technique at reaction temperatures 5, 27 and 65 °C. Synthesized powders were characterized using X-ray diffraction, transmission electron microscope and Brunauer–Emmett–Teller techniques to carry out structural and morphological analysis. The reaction temperature has been found to be playing a crucial role in controlling particle size. It has been observed that Cr{sub 2}O{sub 3} nanoparticles synthesized at 27 °C were smaller as compared to those synthesized at 5 and 65 °C. Chromium oxide samples thus prepared were deposited as thick films on alumina substrates to act as gas sensors and their sensing response to ethanol vapour was investigated at different operable temperatures. It has been observed that all the sensors exhibited optimum response at 250 °C. The investigations revealed that sensing response of Cr{sub 2}O{sub 3} nanoparticles synthesized at 27 °C was exceptionally higher than that of Cr{sub 2}O{sub 3} nanoparticles synthesized at 5 and 65 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effects of High Spinel and Chromium Oxide Crystal Contents on Simulated HLW Vitrification in DM100 Melter Tests (Final Report)

The principal objective of the work was to evaluate the effects of spinel and chromium oxide particles on WTP HLW melter operations and potential impacts on melter life. This was accomplished through a combination of crucible-scale tests, settling and rheological tests, and tests on the DM100 melter system. Crucible testing was designed to develop and identify HLW glass compositions with high waste loadings that exhibit formation of crystalline spinel and/or chromium oxide phases up to relatively high crystal contents (i.e., > 1 vol%). Characterization of crystal settling and the effects on melt rheology was performed on the HLW glass formulations. Appropriate candidate HLW glass formulations were selected, based on characterization results, to support subsequent melter tests. In the present work, crucible melts were formulated that exhibit up to about 4.4 vol% crystallization.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Enhanced photocatalytic degradation of methylene blue dye under UV-sunlight irradiation by cesium doped chromium oxide thin films

Highlights: • Cs doped thin films has been prepared by the low- cost spray pyrolysis technique. • Enhanced photocatalytic activity of Cr2O3 thin films for MB photogegradation(MB) dye was achieved through Cs doping. • 6 % Cs doped Cr{sub 2}O{sub 3} thin film photocatalyst with the merits of low band gap and more oxygen vacancies, exhibits the highest sun-light photocatalytic activity. • High photostability and recyclability was achieved under sun-light irradiation. - Abstract: The present contribution highlights the photocatalytic degradation of methylene blue dye over chromium oxide Cr{sub 2}O{sub 3} thin films based photocatalysts illuminated by ultraviolet and sunlight. Cr{sub 2}O{sub 3} photocatalyst was synthesized as thin film by the spray pyrolysis method on glass substrate at temperature of 350 °C. The physical properties of the thin films were studied by X-ray diffraction, scanning electron microscopy (SEM), infrared spectroscopy (IR), Raman spectroscopy, photoluminescence (PL) probing and UV–vis spectroscopy. XRD results showed that all samples were well crystallized with rhomoboedric curudum structure. Emissions of all films have been observed in visible region at 325 nm excitation. UV–vis-NIR spectrophotometry analysis showed that the band gap energy value of chromium oxide is shortened with cesium doping. Results indicate that both the cesium doping and the introduction of oxygen vacancies promote good photocatalytic activity of Cs doped Cr{sub 2}O{sub 3} thin films under sunlight for MB degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Amorphous iron–chromium oxide nanoparticles with long-term stability

Highlights: • Fe–Cr oxide nanoparticles with pre-established metals ratio were obtained. • The amorphous state and its long-term stability were highlighted by X-ray diffraction. • The average diameter of dried nanoparticles was 3.5 nm, as was estimated by TEM, AFM. • In hexane dispersion, nanoparticles with diameter in the range 2.33–4.85 nm were found. • Superparamagnetic state of NPs co-exists with diamagnetism of the organic layer. - Abstract: Iron–chromium nanoparticles (NPs) were obtained through the thermal decomposition of μ{sub 3}-oxo heterotrinuclear (FeCr{sub 2}O) acetate in the presence of sunflower oil and dodecylamine (DA) as surfactants. The average diameter of the NPs was 3.5 nm, as estimated on the basis of transmission electron microscopy and atomic force microscopy images. Both techniques revealed the formation of roughly approximated spheres with some irregularities and agglomerations in larger spherical assemblies of 50–100 nm. In hexane, NPs with diameters in the 2.33–4.85 nm range are individually dispersed, as emphasized by dynamic light scattering measurements. The amorphous nature of the product was emphasized by X-ray powder diffraction. The study of the magnetic properties shows the presence of superparamagnetic state of iron–chromium oxide NPs and the diamagnetic contribution from DA layer forming a shell of NPs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Synthesis, characterization, and crystal structures of uranyl compounds containing mixed chromium oxidation states

The mixed-valence chromium uranyl compounds Li{sub 5}[(UO{sub 2}){sub 4}(Cr(V)O{sub 5})(Cr(VI)O{sub 4}){sub 4}](H{sub 2}O){sub 17} (1), (Mg(H{sub 2}O){sub 6}){sub 5}[(UO{sub 2}){sub 8}(Cr(V)O{sub 5}){sub 2}(Cr(VI)O{sub 4}){sub 8}] (2) and (NH{sub 4}){sub 5}[(UO{sub 2}){sub 4}(Cr(V)O{sub 5})(Cr(VI)O{sub 4}){sub 2}]H{sub 2}O{sub 11} (3) have been synthesized and characterized. Each contains an identical sheet of cation-centered polyhedra. Central to the connectivity of the sheet are four uranyl pentagonal bipyramids that share some of their equatorial vertices, giving a four-membered ring. The Cr(V) cation located near the center of this ring is coordinated by O atoms in a square pyramidal arrangement. The Cr(VI) is tetrahedrally coordinated by O atoms, and these tetrahedra link the four-membered rings of bipyramids. The mixed-valence nature of the sheet was verified by XANES, an EPR spectrum, and bond-valence analysis. Low-valence cations and H{sub 2}O groups reside between the sheets of uranyl and chromate polyhedra, where they provide linkages between adjacent sheets. - Graphical abstract: Three uranyl chromate compounds contain both pentavalent and hexavalent chromium. The unusual topology of the uranyl chromate sheet contains unusual pentavalent chromium in a square pyramidal coordination environment. Highlights: Black-Right-Pointing-Pointer The first uranyl compounds with mixed Cr valences are reported. Black-Right-Pointing-Pointer A sheet of uranyl polyhedra stabilizes pentavalent chromium. Black-Right-Pointing-Pointer Uranyl and chromate polyhedra form a topologically novel sheet.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Preparation of amorphous copper - chromium oxides catalysts for selective oxidation of cyclohexane

In this work, amorphous copper-chromium catalysts with different Cu/Cr molar ratios have been prepared by a sol-gel method and were used in the oxidation of cyclohexane to KA-oil. The catalysts have been characterized by a variety of analytical techniques including XRD, XPS, Raman, FT-IR, BET, TEM and SEM. XRD results confirmed that the formation of amorphous structure. Here, the XPS and Raman results indicated that most of Cu species existed in well-dispersed tetrahedral coordination before calcination. After calcination, the tetrahedrally coordinated Cu ions are transformed into octahedral coordination and the activity of catalyst is significantly reduced. The results show that the tetrahedrally coordinated Cu ions play the synergistic catalytic role with Cr ions. Interestingly, oxidation of cyclohexane is more inclined to produce cyclohexanol with uncalcined catalyst due to the presence of the tetrahedrally coordinated Cu ions; however, the appearance of surface lattice oxygen makes the reaction more conducive to cyclohexanone after calcination. After optimizing conditions, Cu-Cr oxide catalyst with the molar ratio 1:1 shows the highest activity, which obtains 62.2% yield and 92.4% selectivity for KA-oil using H 2 O 2 as oxygen source.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Bifacial CdTe Solar Cells with Copper Chromium Oxide Back-Buffer Layer

Bifacial solar cells have the potential to maintain energy output higher than monofacial devices under unfavorable weather conditions. A transparent back-buffer layer which can passivate the interface and improve the minority carrier lifetime is critical in CdTe-based bifacial devices. Herein, solution-processed Cu x Cr y O z as a promising back-buffer for CdTe/CdS solar cells is demonstrated. The carrier lifetimes measured at the front and back of the device are 31.2 and 3.1 ns, respectively, which correspond to an increase of ≈38% and 138%, respectively, compared to the reference device. This dramatic improvement in lifetime results in a 100% increase in short-circuit current measured with backside illumination. The best bifacial device has efficiencies 7.6% and 12.5%, respectively, from back and front illumination, yielding a bifaciality factor of 0.60.

14 SOLAR ENERGY↗
DOE OSTI2023

Elucidation of puzzling questions regarding the CrO x /Al 2 O 3 catalyst I. X-ray absorption spectroscopy aided identification of the nature of the chromium oxide species in the CrO x /Al 2 O 3 dehydrogenation catalyst system

The CATOFIN© process produces propylene from propane using a CrO x /Al 2 O 3 catalyst. Despite its use, there are still uncertainties surrounding the nature of Cr species formed during synthesis, regeneration, and aging. It has been observed that ppm levels of Cr 2 O 3 can be oxidized to Cr(VI) in air; however, when Cr 2 O 3 is in direct contact with Al 2 O 3 , Cr(VI) formation increased more than 100-fold. Here, to confirm physical contact between Cr 2 O 3 and Al 2 O 3 results in increased Cr(VI) formation, Cr 2 O 3 and Cr 2 O 3 /Al 2 O 3 samples were synthesized, calcined, and characterized. Catalytic activity measurements confirm propylene selectivity inversely tracks with Cr(VI). Wet chemical titration and X-ray absorption spectroscopy (XAS) quantified and determined the structure of the Cr(VI) species. FEFF X-ray absorption near edge structure simulations determined the potential sensitivity of the XAS to the presence of Al 3+ /Cr 3+ neighboring atoms. XAS correlated to FEFF simulations suggested that Al 3+ x Cr 3+ 2–x Cr 6+ 3 O 12 comprises a significant fraction of the Cr(VI) species formed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Vibrational sum frequency generation spectroscopy reveals the inertness of chromium oxide (001) surfaces

Nanoengineered metal oxides such as Cr(III)-oxide (chromia) films have diverse potential applications in corrosion inhibition, remediation, energy generation, catalysis, data storage, and biological and environmental systems. Concerns about material degradation or oxidation to toxic chromate necessitate an understanding of chromia/aqueous interfaces, beginning with their hydroxylation and hydration behavior. Vibrational sum-frequency generation spectroscopy (vSFG) provides specific molecular-level information about water at the oxide/aqueous junction with high surface selectivity. To overcome the strong absorber problem typical of certain metal oxides in the UV–visible range during nonlinear optical studies, we employed molecular beam epitaxy to deposit transparent, epitaxial nanofilms of Cr 2 O 3 with (001) crystalline orientation on sapphire (Al 2 O 3 (001)) substrates, as confirmed by atomic force microscopy and X-ray diffraction. vSFG spectra of the air and water interfaces of the Cr 2 O 3 (001) films reveal hydroxyl features corresponding to both dissociated and molecular water on the surface. In contrast to the dangling hydroxyls found on the bare Al 2 O 3 (001) substrate, the hydroxyl groups on the deposited Cr 2 O 3 (001) nanofilm do not readily undergo isotopic H/D exchange when exposed to varying forms of D 2 O under ambient conditions. When considering the chemistries of the corresponding trivalent cations in aqueous solution, the finding is at variance with their similar acidities and proton exchange dynamics but consistent with markedly slower inner-sphere water ligand exchange of hexaquo Cr 3+ . This finding challenges the idea that proton and water exchange at the water/Cr₂O₃(001) interface are solely correlated, driven by the strength of metal-bridging oxygen bonds and surface hydroxyl distribution, without direct causation.

Boamah-Agyemang, Mavis D. [Pacific Northwest Natio↗
DOE OSTI2017

First-Principles Study of the Voltage Profile and Mobility of Mg Intercalation in a Chromium Oxide Spinel

The development of Mg batteries, which can potentially achieve higher energy densities than Li-ion systems, is in need of cathodes that can reversibly intercalate Mg 2+ and exhibit a higher energy density than the state-of-the-art Chevrel and thio-spinel cathodes. Recent theoretical and experimental studies indicate that the oxide spinel family presents a set of promising Mg cathodes. Here specifically, in this work, we investigate Mg intercalation into the spinel-MgxCr 2 O 4 system. Using first-principles calculations in combination with a cluster expansion model and the nudged elastic band theory, we calculate the voltage curve for Mg insertion at room temperature and the activation barriers for Mg diffusion, respectively, at different Mg concentrations in the Cr 2 O 4 structure. Our results identify a potential limitation to Mg intercalation in the form of stable Mg-vacancy orderings in the Cr 2 O 4 lattice, which exhibit high migration barriers for Mg diffusion in addition to a steep voltage change. Additionally, we propose cation substitution as a potential mechanism that can be used to suppress the formation of the stable Mg-vacancy ordering, which can eventually enable the practical usage of Cr 2 O 4 as a Mg-cathode.

25 ENERGY STORAGE↗