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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Crystalline Organic Compounds as Effective Nuclei in Contact Efflorescence of Ammonium Sulfate

Contact nucleation is believed to play a role in liquid-to-solid phase transitions in the atmosphere including ice nucleation and salt efflorescence. Here, for this work, contact efflorescence of optically levitated ammonium sulfate droplets by collisions with organic particles is probed using a long working-distance optical trap. Two highly viscous water-soluble organic compounds (d-(+)-raffinose and citric acid), and two insoluble highly surface-active organic compounds (stearic acid and cis-pinonic acid) were probed for their ability to induce efflorescence upon contact. While three of the organics showed minimal effectiveness as contact nuclei, cis-pinonic acid showed a remarkable ability to initiate contact efflorescence of ammonium sulfate, occurring near ammonium sulfate’s deliquescence relative humidity. Further analysis of cis-pinonic acid using bright-field microscopy in an electrodynamic balance provided evidence that the cis-pinonic acid particles are crystalline under the laboratory conditions. We suggest that the close lattice match between crystalline ammonium sulfate and crystalline cis-pinonic acid may account for the observed effectiveness in initiating contact efflorescence of ammonium sulfate. In contrast, tests of contact nucleation between cis-pinonic acid and sodium chloride, a pair with a poor lattice match, did not result in efflorescence. These findings suggest that crystalline organic compounds in the atmosphere could act as effective nuclei for contact efflorescence of atmospherically relevant salts, provided they share a compatible lattice structure.

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

Structure Evolution of Chemically Degraded ZIF-8

Exposure of the metal–organic zeolitic imidazolate framework-8 (ZIF-8) to humid SO x gas cleaves Zn–N bonds, leading to framework disorder and a corresponding decrease in pore accessibility. This work shows that framework disorder exhibits a critical behavior with respect to water concentration in the gas stream. While the quantity of sulfate adsorbed at Zn nodes is at or below the detection threshold for the X-ray pair distribution function technique, precluding direct observation of the adsorbate, powder diffraction reveals clear structural alterations. Here, the onset of linker cleavage correlates to a large microstrain that diminishes as framework disorder increases. Energy-dispersive X-ray spectroscopy shows that the sulfur distribution throughout representative grains is uniform, implying the structure transformation is homogeneously nucleated and not dependent upon gas diffusion kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Ab Initio Simulations of Tritium Diffusion in Al-Rich Iron Aluminide Coating Phases

Surface coatings of steels used in extreme conditions and corrosive environments generally aim to provide protection and increased durability. In the case of tritium-producing burnable absorber rods (TPBARs) used in nuclear reactors, a 316 stainless steel has been coated with Al. Scanning transmission electron microscopy (STEM) characterization of the coating found three Al-rich (>60 atom % Al) iron aluminide alloys identified as hexagonal FeNiAl 5 , monoclinic Fe 4 Al 13 , and orthorhombic Fe 2 Al 5 . Density functional theory simulations using nudged elastic band have been performed to investigate the diffusion of interstitial tritium in each Al-rich iron aluminide phase. While FeNiAl 5 and Fe 4 Al 13 can be viewed as the stacking of two layers, the structural peculiarity of Fe 2 Al 5 is that channels of variable Al vacancy content are present along the c-axis. Therefore, three stoichiometries for Fe 2 Al x phase, namely, Fe 2 Al 4 , Fe 2 Al 5 , and Fe 2 Al 6 , have been considered to evaluate the impact of Al vacancy concentration on tritium diffusion behavior. Altogether, we found that at 600 K, tritium diffusion decreases from a faster rate in the channels of Fe 2 Al x phases (D T ≤ 10 –11 m 2 ·s –1 ) to Fe 4 Al 13 (D T ≈ 10–12 m2·s–1), and finally in FeNiAl5 (D T ≈ 10 –13 m 2 ·s –1 ). Here, we also find that interstitial tritium generally diffuses faster in Fe–Al coating phases than in the tritium breeding material γ-LiAlO 2 (D T ≈ 10 –14 m 2 ·s –1 ) but slightly slower than in 316 stainless steel (D T ≈ 10 –10 m 2 ·s –1 ).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O 2−δ Nanoparticles

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. Here, in this work, Pr 0.2 Ce 0.8 O 2−δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strain and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO 2 (1 to 10 –4 atm O 2 ). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO 2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO 2 . STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.

ceria↗
DOE OSTI2020

Ni Nanoparticles on CeO 2 (111): Energetics, Electron Transfer, and Structure by Ni Adsorption Calorimetry, Spectroscopies, and Density Functional Theory

The morphology, interfacial bonding energetics and charge transfer of Ni clusters and nanoparticles on slightly-reduced CeO 2-x (111) surfaces at 100 to 300 K have been studied using single crystal adsorption calorimetry (SCAC), low-energy ion scattering spectroscopy (LEIS), Xray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and density functional theory (DFT). The initial heat of adsorption of Ni vapor decreased with the extent of pre-reduction (x) of the CeO 2-x (111), showing that stoichiometric ceria adsorbs Ni more strongly than oxygen vacancies. On CeO 1.95 (111) at 300 K, the heat dropped quickly with coverage in the first 0.1 ML, attributed to nucleation of Ni clusters on stoichiometric steps, followed by the Ni particles spreading onto less favorable terrace sites. At 100 K, the clusters nucleate on terraces due to slower diffusion. Adsorbed Ni monomers are in the +2 oxidation state, and they bind by ~45 kJ/mol more strongly to step sites than terraces. The measured heat of adsorption versus average particle size on terraces is favorably compared to DFT calculations. The Ce 3d XPS lineshape showed an increase in Ce 3+ /Ce 4+ ratio with Ni coverage, providing the number of electrons donated to the ceria per Ni atom. The charge transferred per Ni is initially large but strongly decreases with increasing cluster size for both experiments and DFT, and shows large differences between clusters at steps versus terraces. This charge is localized on the interfacial Ni and Ce atoms in their atomic layers closest to the interface. This knowledge is crucial to understanding the nature of the active sites on the surface of Ni-CeO 2 catalysts for which metal-oxide interactions play a very important role in the activation of O-H and C-H bonds. In conclusion, the changes in these interactions with Ni particle size (metal loading) and the extent of reduction of the ceria help to explain how previously reported catalytic activity and selectivity change with these same structural details.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Scanning Kelvin Probe Microscopy Reveals That Ion Motion Varies with Dimensionality in 2D Halide Perovskites

We study ion migration in 2D lead halide perovskites of varying dimensionality using scanning Kelvin probe microscopy (SKPM). We perform potentiometry on micrometer-scale lateral junctions in the absence of injected charge, and we compare how ion motion varies between prototypical two-dimensional n-butylammonium lead iodide perovskites (BA 2 PbI 4 , n = 1), and methylammonium-incorporated quasi-2D perovskites (BA 2 MA 3 Pb 4 I 13 , ~ < n > = 4) under the effects of illumination and temperature. We attribute the observed slow dynamics to relaxation of the bias-induced ionic charge distributions at different temperatures, and we extract the activation energies associated with the ionic motion in each case. Lastly, we propose an explanation for these phenomena by hypothesizing that ion motion in purely-2D BA 2 PbI 4 perovskite films is dominated by paired halide and halide vacancy, whereas for quasi-2D BA 2 MA 3 Pb 4 I 13 perovskites, the ion motion is a combination of both halide and methylammonium (vacancy) migration. These data show that dimensionality in these systems plays a critical role in ion dynamics.

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

Inhomogeneous Magnetic Anisotropy in an Fe 5– x GeTe 2 Nanoflake Observed by Imaging

Few-layer flakes of ferromagnetic Fe 5–x GeTe 2 with x = 0.3 (F5GT) possess a c-axis magnetocrystalline anisotropy that is large enough below ∼200 K to outcompete the easy-plane shape anisotropy, yielding distinctive magnetic microstructures with out-of-plane (OOP) magnetizations. Using photoemission electron microscopy (PEEM) with magnetic contrast from X-ray magnetic circular dichroism (XMCD) to study a thermally demagnetized h-BN-protected nanoflake of F5GT at 110 K, we observe a micron-scale coexistence between domains with OOP magnetizations (∼70% areal fraction) and hitherto unknown domains in which in-plane (IP) magnetization components dominate (∼30% areal fraction). The regions with dominant IP magnetization components do not correlate with small variations of flake thickness (6–10 nm) and instead arise from local changes of magnetocrystalline anisotropy due to a hitherto unidentified chemical inhomogeneity that we suggest to be a higher concentration of Fe vacancies. Our observation of micron-scale inhomogeneity would likely be missed if imaging a single flake orientation and should affect the viability and performance of van der Waals (vdW) spintronic devices with F5GT electrodes.

2D materials↗
DOE OSTI2020

CO Oxidation Mechanisms on CoO x -Pt Thin Films

The reaction of CO and O 2 with submonolayer and multilayer CoO x films on Pt(111), to produce CO 2 , was investigated at room temperature in the mTorr pressure regime. Here, using operando ambient pressure X-ray photoelectron spectroscopy and high pressure scanning tunneling microscopy, as well as density functional theory calculations, we found that the presence of oxygen vacancies in partially oxidized CoO x films significantly enhances the CO oxidation activity to form CO 2 upon exposure to mTorr pressures of CO at room temperature. In contrast, CoO films without O-vacancies are much less active for CO 2 formation at RT, and CO only adsorbed in the form of carbonate species that are stable up to 260 °C. On submonolayer CoO x islands, the carbonates form preferentially at island edges, deactivating the edge sites for CO 2 formation, even while the reaction proceeds inside the islands. These results provide a detailed understanding of CO oxidation pathways on systems where noble metals such as Pt interact with reducible oxides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Disentangling Oxygen and Water Vapor Effects on Optoelectronic Properties of Monolayer Tungsten Disulfide

By understanding how the environmental composition impacts the optoelectronic properties of transition metal dichalcogenide monolayers, we demonstrate that simple photoluminescence (PL) measurements of tungsten disulfide (WS 2 ) monolayers can differentiate relative humidity environments. In this paper, we examine the PL and photoconductivity of chemical vapor deposition grown WS 2 monolayers under three carefully controlled environments: inert gas (N 2 ), dry air (O 2 in N 2 ), and humid nitrogen (H 2 O vapor in N 2 ). The WS 2 PL is measured as a function of 532 nm laser power and exposure time and can be decomposed into the exciton, trion, and lower energy state(s) contributions. Under continuous illumination in either O 2 or H 2 O vapor environment, we find dramatic (and reversible) increases in PL intensity relative to the PL in an inert environment. The PL bathochromically shifts in an O 2 environment and is dominated by increased trion emission and diminished exciton emission. In contrast, the WS 2 PL increase in a H 2 O environment results from an overall increase in emission from all spectral components where the exciton contribution dominates. The drastic increases in PL are anticorrelated with corresponding decreases in photoconductivity, as measured by time-resolved microwave conductivity. The results suggest that both O 2 and H 2 O react photochemically with the WS 2 monolayer surface, modifying the optoelectronic properties, but do so via distinct pathways. Thus, we use these optoelectronic differences to differentiate the amount of humidity in the air, which we show with 0%, 40%, and 80% relative humidity environments. This deeper understanding of how ambient conditions impact WS 2 monolayers enables novel humidity sensors as well as a better understanding of the correlation between TMDC surface chemistry, light emission, and photoconductivity. Moreover, these WS 2 measurements highlight the importance of considering the impact of the local environment on reported results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Revealing the Latent Atomic World Through Data-Driven Microscopy

Many emerging technologies depend on the precise design of materials structure, chemistry, and defects. As devices shrink, manufacturing tolerances tighten, and performance envelopes improve, we must increasingly measure and manipulate materials at or near the single atom level. Here we describe how transmission electron microscopy (TEM) underpins our ability to see and direct the latent atomic world. We review a selection of our recent high-resolution TEM studies of the synthesis of oxide-based nanomaterials and their evolution in extreme environments. We then discuss powerful new artificial intelligence (AI) and machine learning (ML) approaches we have developed for rich, reproducible, and scalable experimentation. Furthermore, we conclude by discussing future developments that will enable new materials for breakthrough technologies.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Unequal {110} Facets: The Potential Role of Intraparticle Heterogeneity and Facet Termination in Photoelectrochemical Activity of Single BiVO 4 Particles

BiVO 4 photoanodes are promising for solar water splitting, with photogenerated electrons and holes preferentially reacting at top {010} and lateral {110} facets, respectively. However, the mechanisms driving this facet-dependent reactivity remain unclear. Here, in this study, we investigate facet-dependent photocurrent and material heterogeneity using correlative scanning photoelectrochemical microscopy (SPCM), electron beam induced current (EBIC) mapping, and mid-IR scattering scanning near-field optical microscopy (s-SNOM). SPCM measurements of 62 BiVO 4 particles confirmed higher photocurrents at lateral {110} facets compared to top {010} facets, but unexpectedly revealed variations in photocurrent among lateral facets within the same particle. Variations in lateral facet surface termination could explain the intraparticle-level reactivity heterogeneity, consistent with theoretical predictions. Nano-FTIR spectroscopy and Raman microspectroscopy indicated significant materials chemistry heterogeneity within individual particles and facets that could be attributed to variations in lattice vibration distortions that enhance the overlap between Bi 6s and O 2p orbitals. The increased orbital overlap is significant as it potentially increases hole mobility in the valence band and potentially explains the lateral facet-dependent charge separation efficiency observed in photocurrent maps. Facet-dependent electrical and EBIC measurements showed no space charge regions at interfacet junctions or metal-BiVO 4 contacts under vacuum, suggesting that photogenerated holes beneath top {010} facets are unlikely to transport to lateral {110} facets to drive water/sulfite oxidation. These findings indicate the potential influence of distinct bulk properties and surface termination chemistries across different particles and facets, highlighting the importance of carefully controlling defects and surface chemistry during sample growth to optimize photocatalytic performance.

BiVO4↗
DOE OSTI2020

High-throughput screening for discovery of benchtop separations systems for selected rare earth elements

Abstract Rare earth (RE) elements (scandium, yttrium, and the lanthanides) are critical for their role in sustainable energy technologies. Problems with their supply chain have motivated research to improve separations methods to recycle these elements from end of life technology. Toward this goal, we report the synthesis and characterization of the ligand tris[(1-hydroxy-2-oxo-1,2-dihydropyridine-3-carboxamido)ethyl]amine, H 3 1·TFA (TFA = trifluoroacetic acid), and complexes 1·RE (RE = La, Nd, Dy). A high-throughput experimentation (HTE) screen was developed to quantitatively determine the precipitation of 1·RE as a function of pH as well as equivalents of H 3 1·TFA. This method rapidly determines optimal conditions for the separation of RE mixtures, while minimizing materials consumption. The HTE-predicted conditions are used to achieve the lab-scale separation of Nd/Dy ( SF Nd/Dy = 213 ± 34) and La/Nd ( SF La/Nd = 16.2 ± 0.2) mixtures in acidic aqueous media.

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

Chemical Interpretation of Charged Point Defects in Semiconductors: A Case Study of Mg 2 Si

The electronic structures of charged point defects influence electrical and optical properties of semiconductors. Understanding the orbital interactions responsible for the electronic structures of defects therefore promotes a chemical intuition for defect-driven mechanisms in semiconductors. In this tutorial, we discuss a molecular orbital theory-based framework for understanding defect-induced electronic states based on local chemical interactions between the defect and the atoms surrounding the defect site. By using Mg 2 Si as a case study, we show how both the chemical interactions and molecular orbitals (i. e., wave functions) responsible for the charge state(s) of a defect can be understood from the bonding symmetry of the defect site. We anticipate that a chemistry-based perspective of charged defects will enrich defect engineering efforts for electronic and optical materials.

36 MATERIALS SCIENCE↗