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Results for “Oxide Phase Formation”

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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The effects of vanadium substitution on one-dimensional tunnel structures of cryptomelane: Combined TEM and DFT study

Rational design of energy storage materials requires mechanistic understanding which relies on atomic scale characterization of structure and defects. In this paper we utilize vanadium (V)-substituted one-dimensional cryptomelane as a model material to study structural features critical to electrochemical reversibility of the cathode in lithium-ion batteries. We found the substitution of manganese (Mn) atoms in the tunnel wall with V enhances structural uniformity in the parent KMn 8 O 16 material by inhibiting formation of irregular (2 × 3 and 2 × 1) manganese oxide tunnel structures. Upon lithiation, both transmission electron microscopy (TEM) and density functional theory (DFT) reveal significant structural evolution, eventually resulting in phase separation and formation of highly reduced manganese oxide. During this process, Mn 4+ accepts electrons donated by intercalated Li, while the V 4+ substituent is not electrochemically reduced but acts to stabilize the tunnel framework structure. As a result, the V substituted material shows higher operating voltage and improved electrochemical reversibility. Our results highlight the benefits of V-substitution in cryptomelane, and the significance of integrating characterization with simulation for understanding and developing design principles for lithium ion battery materials.

25 ENERGY STORAGE↗
DOE OSTI2016

The effect of sub-oxide phases on the transparency of tin-doped gallium oxide

There have been a number of studies on the fabrication of Sn-doped gallium oxide (Ga 2 O 3 :Sn) films with both conductive and transparent properties using a variety of deposition methods. However, often, synthesis results in films that are not transparent. In this paper, we examine the mechanisms underlying these results in Ga 2 O 3 :Sn thin films prepared at various growth temperatures, Sn concentrations, and oxygen partial pressures. With X-ray absorption spectroscopy, transmission electron microscopy and energy dispersive spectroscopy, we find that when films are grown under the oxygen deficient conditions there are Ga sub-oxide and SnOx phases in the Ga 2 O 3 :Sn thin film. These Ga sub-oxide phases are only found in non-transparent films, and so we infer that the Ga sub-oxide is responsible for the non-transparency. These observations suggest that to obtain transparent Ga 2 O 3 :Sn, films deposition or subsequent annealing must be carefully controlled in both temperature and oxygen partial pressure to avoid the formation of Ga sub-oxide phases.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Irradiation-induced formation of a spinel phase at the FeCr/MgO interface

Oxide dispersion strengthened ferritic/martensitic alloys have attracted significant attention for their potential uses in future nuclear reactors and storage vessels, as the metal/oxide interfaces act as stable high-strength sinks for point defects while also dispersing helium. Here, in order to unravel the evolution and interplay of interface structure and chemistry upon irradiation in these types of materials, an atomically sharp FeCr/MgO interface was synthesized at 500 °C and separately annealed and irradiated with Ni 3+ ions at 500 °C. After annealing, a slight enrichment of Cr atoms was observed at the interface, but no other structural changes were found. However, under irradiation, sufficient Cr diffuses across the interface into the MgO to form a Cr-enriched transition layer that contains spinel precipitates. First-principles calculations indicate that it is energetically favorable to incorporate Cr, but not Fe, substitutionally into MgO. Furthermore, our results indicate that irradiation can be used to form new phases and complexions at interfaces, which may have different radiation tolerance than the pristine structures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Redistribution of Erbium and Oxygen Recoil Atoms and the Structure of Silicon Thin Surface Layers Formed by High-Dose Argon Implantation through Er and SiO{sub 2} Surface Films

Using analytical high-resolution electron microscopy, the Si structure and the redistribution of Er and O recoil atoms embedded in thin (~10 nm) surface layers by Ar{sup +} implantation with an energy of 250–290 keV and a dose of 1 × 10{sup 16} cm{sup –2} through Er and SiO{sub 2} films, respectively, and subsequent annealing are studied. It is established that Si recrystallization fails at a distance of ~20 nm from the surface, where the erbium concentration of 5 × 10{sup 19} cm{sup –3} critical for failure is achieved at T = 950°C. It disproves the generally accepted model of Er-atom transfer by the recrystallization front into SiO{sub 2} on the surface. Instead, it is shown that the redistribution of O recoil atoms to the initial oxide during annealing for immobile Er atoms provides the formation of surface-inhomogeneous erbium phases in such a way that the oxygen-enriched Er–Si–O phase turns out to be concentrated in the oxide, while the depleted Er–Si phase remains in Si. It explains the partial loss of implanted Er after removal of the oxide together with the Er–Si–O phase. It was shown that the formation of a high density of microtwins (locally up to 10{sup 13} cm{sup –2}) is associated with the formation of Ar bubbles and clusters, which is atypical for (100)–Si recrystallization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Modern insights into the mechanisms of neptunium oxalate decomposition

Neptunium oxalate (Np(C 2 O 4 ) 2 ·6H 2 O) is a historically relevant solid phase used in nuclear processing as a precursor for neptunium dioxide (NpO 2 ). Although Np oxalate has been synthesized and used for NpO 2 production for decades, the thermal decomposition mechanism of this phase remains poorly understood and has not been evaluated in over 30 years. Conflicting reports in historical literature suggest either a direct conversion from anhydrous oxalate to NpO 2 or a decomposition that includes the formation of Np carbonate or oxidized Np intermediate phases. In this work, we reexamine the decomposition pathway of Np(C 2 O 4 ) 2 ·6H 2 O using thermal analysis coupled with evolved gas analysis and temperature-dependent Raman spectroscopy to elucidate decomposition mechanisms and intermediate phases using modern analytical techniques. Thermal analysis revealed a three-stage decomposition process, including dehydration below 200 °C, oxalate breakdown between 170 and 370 °C, and NpO 2 formation by 500 °C. However, an unidentified plateau in the thermal data was observed during measurements. Raman spectroscopy confirmed the stages of decomposition, and in the analysis of potential intermediate phases, no carbonate phases or Np 2 O 5 were identified. Raman data suggest that residual oxalate or nonstoichiometric oxide are present during decomposition before pure NpO 2 is formed. These findings clarify aspects of the Np oxalate decomposition mechanism and address longstanding discrepancies in the literature, with a specific focus on Np-specific materials chemistry.

Lawson, Kathryn M. [Oak Ridge National Laboratory ↗
DOE OSTI2022

Near-infrared spectra and molar absorption coefficients of trivalent lanthanides dissolved in molten LiCl–KCl eutectic

Determining the concentration of the dissolved lanthanide species in LiCl–KCl eutectic salt is important to the development of pyrochemical reprocessing of used nuclear fuel. In this process, lanthanide fission products are found dissolved in the electrorefiner electrolyte in their trivalent oxidation state. The presence of dissolved trivalent lanthanides increases the liquidus temperature of the electrolyte mixture and can lead to the formation of insoluble oxide or oxychloride phases and must therefore be continuously monitored and controlled during the operation. Absorbance spectroscopy is a promising method for continuous measurement of the concentration of lanthanides and other elements dissolved in the electrolyte. The absorption of light by elements is linearly proportional to the concentration of the element for relatively dilute solutions according to the Beer-Lambert law. Although measurement of the absorption of ultraviolet and visible range light by lanthanides in LiCl–KCl eutectic molten salt have been explored previously, near infrared (NIR) absorption spectroscopy has received far less attention. It may, however, provide a better analytical signal when insoluble phases are present due to less Raleigh scattering compared to shorter wavelength radiation. Additionally, it may allow for concentration determination for certain elements using NIR absorption features where UV and visible range features are overlapping with features from other species. In this study, we report the UV–Vis–NIR spectra of the trivalent lanthanide chlorides of neodymium, samarium, and dysprosium in LiCl–KCl eutectic. Molar absorption coefficients are reported for analytically useful absorption maxima, with a focus on the molar absorption coefficients for NIR absorption maxima which have not been reported previously. Additionally, we observe a NIR-range absorption band of Nd3+ which was previously predicted but never experimentally observed. Here, we compare the calculated crystal field levels to the newly observed absorbance band and find them to be in good agreement with previous predictions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Nitridation Temperature Effects on Electronic and Chemical Properties of (Ga 1-x Zn x )(N 1-x O x ) Solid Solution Nanocrystals

Solid solution nanocrystals of gallium nitride–zinc oxide have been realized as potential photocatalysts for visible light driven overall water splitting. The band gap of these materials has been found to narrow further into the visible region as a function of increasing zinc oxide concentration, and thus, it is desirable to synthesize zinc oxide-rich gallium nitride–zinc oxide solid solutions. In this paper, we discuss the effects of using nitridation temperature to control zinc oxide content on the electronic and chemical properties of gallium nitride–zinc oxide solid solution nanostructures. The effect of nitridation temperature was studied using X-ray absorption fine structure (XAFS), including both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), and X-ray excited optical luminescence (XEOL). It was determined that using nitridation temperature as a method of controlling zinc oxide concentration results in solid solutions with poor crystallinity, phase separation, and mixed surface oxide formation. These findings suggest that many complications arise from using nitridation temperature to control zinc oxide concentration in gallium nitride–zinc oxide solid solutions, and thus, it is possible that the resultant materials would exhibit poor photocatalytic activity.

Ward, Matthew James↗
DOE OSTI2016

Linearity optimization of atomic layer deposited ZrO{sub 2} metal-insulator-metal capacitors by inserting interfacial Zr-doped chromia layers

In order to improve the electrical behaviour of metal-insulator-metal capacitors with ZrO{sub 2} insulator grown by Atomic Layer Deposition, the influence of the insertion of interfacial Cr layers between Pt electrodes and the zirconia is investigated. An improvement of the α-voltage coefficient of capacitance as low as 567 ppm/V{sup 2} is achieved for a single layer of Cr while maintaining a high capacitance density of 10.7 fF/μm{sup 2} and a leakage current of less than 1.2 × 10{sup −8} A/cm{sup 2} at +1 V. The role of the interface is discussed by means of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy showing the formation of Zr stabilized chromia oxide phase with a dielectric constant of 16.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

An Introduction to Radiation Damage in Minerals and Ceramics [Slides]

Radiation effects in minerals and ceramics are quite distinct from effects observed in metals. This is largely due to interactions between radiation and the electronic structure of insulating materials that are unique compared to metallic conductors. Most notably, insulators exhibit property changes when energetic particles lose energy to electrons in the solid, whereas metals are unaffected by electronic energy losses. In addition, displacive radiation damage effects (atoms being knocked off their lattice sites by energetic particles) are much more complex in insulators, due to the complexities of their crystal structures (multiple cation and anion sublattices). In this presentation, we will focus on the atomistic mechanisms responsible for radiation damage in minerals and ceramics, when energetic particles lose energy while penetrating a solid. We will consider several examples, including (i) irradiation induced color center formation in gemstones; (ii) latent defects in alkali halides (relevance to thermoluminescent detectors); (iii) radioactive decay-induced amorphization of natural minerals; and (iv) extended defect formation and phase stability in complex oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Elucidating the phase transformations and grain growth behavior of O3-type sodium-ion layered oxide cathode materials during high temperature synthesis

Understanding the formation mechanism of layered oxide cathodes via solid-state synthesis is imperative to achieving controllability over their materials properties and electrochemical behaviors. In this work, we investigate the phase and microstructure evolution during the synthesis of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , a model sodium-ion layered oxide cathode, using a combination of imaging, diffraction, and spectroscopic techniques. We unravel the synthetic mechanistic pathways involved in the high-temperature calcination reaction, as well as elaborate the synthesis-microstructure-performance relationship of this material. The formation of the final layered oxide phase involves a gradual transformation through a sodiated oxyhydroxide intermediate. During the reaction, the precursor dehydration reaction dominates at 250–550 °C, while the major sodiation reaction occurs at 550–850 °C. Alongside multiple stages of phase transformations, the final grain structure formation occurs through the continuous growth of the (003) and (104) facets. During the reaction, Mn acts as the charge-compensating element and exhibits depth-dependent characteristics. When the sodiation reaction dominates over dehydration, the reaction intermediates undergo gradual electronic structure changes with increasing temperature, as indicated by the spectral features of TM3d-O2p hybrid states. Calcination duration is also a critical parameter governing the microstructure, surface reactivity, phase fraction distribution and electrochemical performance of the material. The optimal calcination duration was determined to be 18 hours at 850 °C under the conditions evaluated here. Calcination beyond this duration was found to be detrimental to electrochemical performance due to Na and O loss and heterogeneous sodium distribution throughout the particles. Our work sheds light on the complex crystallographic-chemical-microstructural evolution of sodium ion layered oxide cathodes and provides insight into precisely tuning material properties which are intimately linked to battery performances.

25 ENERGY STORAGE↗
DOE OSTI2021

Self-similar mesocrystals form via interface-driven nucleation and assembly

Crystallization by particle attachment (CPA) is a frequently occurring mechanism of colloidal crystallization that results in hierarchical morphologies. CPA has been exploited to create nanomaterials with unusual properties and is implicated in the development of complex mineral textures. Oriented attachment–a form of CPA in which particles align along specific crystallographic directions–produces mesocrystals that diffract as single crystals do, although the constituent particles are still discernible. The conventional view of CPA is that nucleation provides a supply of particles that aggregate via Brownian motion biased by attractive interparticle potentials. However, mesocrystals often exhibit regular morphologies and uniform sizes. Although many crystal systems form mesocrystals and individual attachment events have been directly visualized10, how random attachment events lead to well defined, self-similar morphologies remains unknown, as does the role of surface-bound ligands, which are ubiquitous in nanoparticle systems. Attempts to understand mesocrystal formation are further complicated in many systems by the presence of precursor nanoparticles with a phase distinct from that of the bulk. Some studies propose that such particles convert before attachment, whereas others attribute conversion to the attachment process itself and yet others conclude that transformation occurs after the mesocrystals exceed a characteristic size. Here we investigate mesocrystal formation by iron oxides, which are important colloidal phases in natural environments and classic examples of systems forming ubiquitous precursor phases and undergoing CPA accompanied by phase transformations. Combining in situ transmission electron microscopy (TEM) at 80 degrees Celsius with ‘freeze-and-look’ TEM, we tracked the formation of haematite (Hm) mesocrystals in the presence of oxalate (Ox), which is abundant in soils, where iron oxides are common. In this work, we find that isolated Hm particles rarely appear, but once formed, interfacial gradients at the Ox-covered surfaces drive Hm particles to nucleate repeatedly about two nanometres from the surfaces, to which they then attach, thereby generating mesocrystals. Comparison to natural and synthetic systems suggests that interface-driven pathways are widespread.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Plasma-droplet interaction study to assess transport limitations and the role of • OH, O • ,H • ,O 2 (a 1 Δ g ),O 3 , He(2 3 S) and Ar(1s 5 ) in formate decomposition

Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of •OH as well as non-•OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O 2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as O• and H• atoms, singlet delta oxygen (O 2 (a 1 Δ g )), O 3 and metastable atoms of He and Ar, besides •OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ~70% decomposition occurring within ~15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase •OH flux at lower H 2 O concentrations with a significant enhancement in the formate decomposition at the lowest water concentration, attributed to e – /ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous •OH concentrations. Here, the formate decomposition in He/O 2 plasma was similar, although with an order of magnitude higher O• radical density than the •OH density in the corresponding He/H 2 O plasma. Using a one-dimensional reaction–diffusion model, we showed that O 2 (a 1 Δ g ) and O 3 did not play a significant role and the decomposition was due to O•, and possibly •OH generated in the vapor containing droplet-plasma boundary layer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Surface Layers of Zr-18%Nb Alloy Modified by Ultrasonic Impact Treatment: Microstructure, Hardness and Corrosion

Near-surface layers in Zr-18%Nb alloy were modified using ultrasonic impact treatment (UIT). The effects of the UIT processing time on a microstructural formation, omega/alpha precipitations, microhardness and corrosion are analyzed. XRD analysis, TEM and SEM observations and EDX characterization allow establishing the links between the microstructure, microhardness and corrosion behavior of the surface layers formed. At the strain extent up to e ≈ 0.3, structural formation occurs under influence of deformation induced heating, which facilitates omega precipitation in beta phase and mechanically induced oxygen transport and oxide formation. XRD analysis reveals moderate compressive residual stresses (− 160 MPa) and pronounced {110} texture after the UIT process. Generation of dislocations and hindering of their movement by nanoscale omega precipitates manifest themselves as the broadening of diffraction peaks occurred mainly owing to the lattice microstrains, and they provide marked strain hardening. The enhanced anticorrosion properties of Zr-18%Nb alloy in saline solution were concluded to be a result of the formation of a protective oxide film, {110} texture and compressive stresses.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Exceptional hardness in multiprincipal element alloys via hierarchical oxygen heterogeneities

Refractory multiprincipal element alloys (RMPEAs) are potential successors to incumbent high-temperature structural alloys, although efforts to improve oxidation resistance with large additions of passivating elements have led to embrittlement. RMPEAs containing group IV and V elements have a balance of properties including moderate ductility, low density, and the necessary formability. We find that oxidation of group IV-V RMPEAs induces hierarchical heterogeneities, ranging from nanoscale interstitial complexes to tertiary phases. This microstructural hierarchy considerably enhances hardness without indentation cracking, with values ranging between 12.1 and 22.6 GPa from the oxide-adjacent metal to the surface oxides, a 3.7 to 6.8× increase over the interstitial-free alloy. Our fundamental understanding of the oxygen influence on phase formation informs future alloy design to enhance oxidation resistance and obtain exceptional hardness while preserving plasticity.

Science & Technology - Other Topics↗
DOE OSTI2022

On the Sintering Behavior of Nb2O5 and Ta2O5 Mixed Oxide Powders

A mixed oxide system consisting of Nb2O5 and Ta2O5, was subjected to annealing in air/hydrogen up to 950 °C for 1–4 h to study its sintering behavior. The thermogravimetric–differential scanning calorimetry (TGA–DSC) thermograms indicated the formation of multiple endothermic peaks at temperatures higher than 925 °C. Subsequently, a 30% Ta2O5 and 70% Nb2O5 (mol%) pellet resulted in good sintering behavior at both 900 and 950 °C. The scanning electron microscope (SEM) images corroborated these observations with necking and particle coarsening. The sintered pellets contained a 20.4 and 20.8% mixed oxide (Nb4Ta2O15) phase, along with Ta2O5 and Nb2O5, at both 900 and 950 °C, indicating the possibility of the formation of a solid solution phase. In situ high-temperature X-ray diffraction (XRD) scans also confirmed the formation of the ternary oxide phase at 6 and 19.8% at 890 and 950 °C, respectively. The Hume–Rothery rules could explain the good sintering behavior of the Ta2O5 and Nb2O5 mixed oxides. An oxide composition of 30% Ta2O5 and 70% Nb2O5 (mol%) and a sintering temperature of 950 °C appeared adequate for fabricating well-sintered oxide precursors for subsequent electrochemical polarization studies in fused salts.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microwave synthesis and electrochemical characterization of Mn/Ni mixed oxide for supercapacitor application

Nanostructured Mn/Ni mixed metal oxide was synthesized at ambient temperature by facile microwave irradiation technique. The crystal structure and surface morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. X-ray diffraction analysis confirmed the formation of Mn/Ni mixed oxide in rhombohedral phase and the grain size calculated was found to be 87 nm. The irregular spherical morphology of the prepared sample was exhibited by the SEM images. The characteristic peaks of FTIR at about 630 cm{sup −1} and 749 cm{sup −1} were attributed to the Mn-O and Ni-O stretching vibrations respectively. The presence of both Mn and Ni in the prepared sample was validated by the EDS spectra which in turn confirmed the formation of mixed oxide. Cyclic voltammetry and galvanostatic chargedischarge measurements were employed to investigate the electrochemical performance of the mixed oxide. The cyclic voltammetry curves demonstrated good capacitive performance of the sample in the potential window −0.2V to 0.9V. The charge discharge study revealed the suitability of the prepared mixed oxide for the fabrication of supercapacitor electrode.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

CO oxidation on gold-supported iron oxides: New insights into strong oxide–metal interactions

Very active FeO x –Au catalysts for CO oxidation are obtained after depositing nanoparticles of FeO, Fe 3 O 4 , and Fe 2 O 3 on a Au(111) substrate. Neither FeO nor Fe 2 O 3 is stable under the reaction conditions. Under an environment of CO/O 2 , they undergo oxidation (FeO) or reduction (Fe 2 O 3 ) to yield nanoparticles of Fe 3 O 4 that are not formed in a bulk phase. Using a combined experimental and theoretical approach, we show a strong oxide–metal interaction (SOMI) between Fe 3 O 4 nanostructures and Au(111), which gives the oxide special properties, allows the formation of an active phase, and provides a unique interface to facilitate a catalytic reaction. This work highlights the important role that the SOMI can play in enhancing the catalytic performance of the oxide component in metal–oxide catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

Oxidation of ZrB2-and HfB2-Based Ultra-High Temperature Ceramics: Effects of Ta Additions

Several compositions of ZrB2- and HfB2-based Ultra-High Temperature Ceramics (UHTC) were oxidized in stagnant air at 1627 C in ten minute cycles for times up to 100 minutes. These compositions include: ZrB2 - 20v% SiC, HfB2 - 20v% SiC, ZrB2 - 20v% SiC - 20v% TaSi2, ZrB2 - 33v% SiC, HfB2 - 20v% SiC - 20v% TaSi2, and ZrB2 - 20v% SiC - 20v% TaC. The weight change due to oxidation was recorded. The ZrB2 - 20v% SiC - 20v% TaSi2 composition was also oxidized in stagnant air at 1927 C and in an arc jet atmosphere. Samples were analyzed after oxidation by x-ray diffraction, field emission scanning electron microscopy, and energy dispersive spectroscopy to determine the reaction products and to observe the microstructure. The ZrB2 - 20v% SiC - 20v% TaSi2 showed the lowest oxidation rate at 1627 C, but performed poorly under the more extreme tests due to liquid phase formation. Effects of Ta-additions on the oxidation of the diboride-based UHTC are discussed.

Opila, Elizabeth↗