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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Raman spectroscopic investigation of selected natural uranyl sulfate minerals

Uranyl sulfates are important constituents of uranium ores and represent a significant fraction of U(VI) minerals discovered in recent years owing to their propensity to form in mine tailings and legacy sites related to uranium exploration. Recently, we surveyed all published Raman spectra for uranium minerals and found significantly less easily accessible data available for uranyl sulfates relative to other groups of uranium minerals (Spano et al. 2023). In that work, we described average spectra for groups of uranyl minerals to understand common vibrational spectroscopic features attributable to similarities in oxyanion chemistry among U(VI) minerals, but only data for three uranyl sulfate minerals were included in the study. The present work reports on Raman spectra collected for 18 additional uranyl sulfate minerals. In conclusion, to better understand underlying structural and chemical features that give rise to spectroscopic observables, we relate differences in structural topology, charge-balancing cations, and locality of origin to features observed in the Raman spectra of selected natural uranyl sulfates.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2024

Correlative single-cell hard X-ray computed tomography and X-ray fluorescence imaging

Abstract X-ray computed tomography (XCT) and X-ray fluorescence (XRF) imaging are two non-invasive imaging techniques to study cellular structures and chemical element distributions, respectively. However, correlative X-ray computed tomography and fluorescence imaging for the same cell have yet to be routinely realized due to challenges in sample preparation and X-ray radiation damage. Here we report an integrated experimental and computational workflow for achieving correlative multi-modality X-ray imaging of a single cell. The method consists of the preparation of radiation-resistant single-cell samples using live-cell imaging-assisted chemical fixation and freeze-drying procedures, targeting and labeling cells for correlative XCT and XRF measurement, and computational reconstruction of the correlative and multi-modality images. With XCT, cellular structures including the overall structure and intracellular organelles are visualized, while XRF imaging reveals the distribution of multiple chemical elements within the same cell. Our correlative method demonstrates the feasibility and broad applicability of using X-rays to understand cellular structures and the roles of chemical elements and related proteins in signaling and other biological processes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Hybrid bilayered vanadium oxide electrodes with large and tunable interlayer distances in lithium-ion batteries

The interlayer distances in layered electrode materials, influenced by the chemical composition of the confined interlayer regions, have a significant impact on their electrochemical performance. Chemical preintercalation of inorganic metal ions affects the interlayer spacing, yet expansion is limited by the hydrated ion radii. Herein, we demonstrate that using varying concentrations of decyltrimethylammonium (DTA + ) and cetyltrimethylammonium (CTA + ) cations in chemical preintercalation synthesis followed by hydrothermal treatment, the interlayer distance of hybrid bilayered vanadium oxides (BVOs) can be tuned between 11.1 Å and 35.6 Å. Our analyses reveal that these variations in interlayer spacing are due to different amounts of structural water and alkylammonium cations confined within the interlayer regions. Increased concentrations of alkylammonium cations not only expand the interlayer spacing but also induce local bending and disordering of the V-O bilayers. Electrochemical cycling of hybrid BVO electrodes in non-aqueous lithium-ion cells show that specific capacities decrease as interlayer regions expand, suggesting that the densely packed alkylammonium cations obstruct intercalation sites and hinder Li + ion transport. Furthermore, we found that greater layer separation facilitates the dissolution of active material into the electrolyte, resulting in rapid capacity decay during extended cycling. In conclusion, this study emphasizes that layered electrode materials require both spacious interlayer regions as well as high structural and chemical stabilities, providing guidelines for structural engineering of organic–inorganic hybrids.

25 ENERGY STORAGE↗
DOE OSTI2023

Chemical cartography with LAMOST and Gaia reveal azimuthal and spiral structure in the Galactic disc

Chemical Cartography, or mapping, of our Galaxy has the potential to fully transform our view of its structure and formation. In this work, we use chemical cartography to explore the metallicity distribution of OBAF-type disc stars from the LAMOST survey and a complementary sample of disc giant stars from Gaia DR3. We use these samples to constrain the radial and vertical metallicity gradients across the Galactic disc. We also explore whether there are detectable azimuthal variations in the metallicity distribution on top of the radial gradient. For the OBAF-type star sample from LAMOST, we find a radial metallicity gradient of Δ[Fe/H]/ΔR ~–0.078 ± 0.001 dex kpc –1 in the plane of the disc and a vertical metallicity gradient of Δ[Fe/H]/ΔZ ~–0.15 ± 0.01 dex kpc –1 in the solar neighbourhood. The radial gradient becomes shallower with increasing vertical height, while the vertical gradient becomes shallower with increasing Galactocentric radius, consistent with other studies. We also find detectable spatially dependent azimuthal variations on top of the radial metallicity gradient at the level of ~0.10 dex. Interestingly, the azimuthal variations appear be close to the Galactic spiral arms in one data set (Gaia DR3) but not the other (LAMOST). Furthermore, these results suggest that there is azimuthal structure in the Galactic metallicity distribution and that in some cases it is co-located with spiral arms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Solution-Processable Copper Halide Based Hybrid Materials Consisting of Cationic Ligands with Different Coordination Modes

Here, using cationic ligands containing both aromatic and aliphatic coordination sites, we have synthesized and structurally characterized five new CuX-based hybrid materials consisting of anionic inorganic motifs that also form coordinate bonds with the cationic organic ligands. As a result of the unique bonding nature at the inorganic/organic interfaces, these compounds demonstrate strong resistance toward heat and can be readily processed in solution. They emit light in the visible region ranging from cyan to yellow color, with the highest photoluminescence quantum yield (PLQY) reaching 71%. The influence of the different coordination modes of the ligands on their emission behavior was investigated employing both experimental and theoretical methods, which have provided insight in understanding structure–property relationships in these materials and guidelines for tuning and enhancing their chemical and physical properties.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Elucidating the Interfacial Effects of Nonmetallic Elements on the Dehydrogenation Behavior of Nanoconfined NaAlH 4 in Zeolite-Templated Carbon

Confining materials within nanoscale volumes alters their physical and chemical properties, with positive consequences for energy storage, conversion, and catalysis. The pore structure and composition of scaffolds are essential variables for optimizing these properties, with carbon-based materials being preferred due to their tunable porous structures and chemical versatility. This study investigates the influence of surface functional groups on the dehydrogenation kinetics of nanoconfined NaAlH4 using zeolite-templated carbons (ZTCs). Here we focus on oxygen functional groups commonly present as intrinsic impurities on carbon scaffolds, analyzing three ZTC scaffolds to determine how their concentrations and configurations affect dehydrogenation behavior. Our findings reveal that carbonyl groups enhance charge transfer and destabilize Al–H bonds more effectively than ether or phenol groups. This indicates that the type of oxygen functional group is more critical than the quantity, highlighting the importance of properly tailoring oxygen defects to improve hydrogen storage performance in nanoconfined systems.

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

Investigating the effect of heterogeneities across the electrode|multiphase polymer electrolyte interfaces in high-potential lithium batteries

Polymer electrolytes hold great promise for safe and high-energy batteries comprising solid or semi-solid electrolytes. Multiphase polymer electrolytes, consisting of mobile and rigid phases, exhibit fast ion conduction and desired mechanical properties. However, fundamental challenges exist in understanding and regulating interactions at the electrode|electrolyte interface, especially when using high-potential layered oxide active materials at the positive electrode. Here we demonstrate that depletion of the mobile conductive phase at the interface contributes to battery performance degradation. Molecular ionic composite electrolytes, composed of a rigid-rod ionic polymer with nanometric mobile cations and anions, serve as a multiphase platform to investigate the evolution of ion conductive domains at the interface. Chemical and structural characterizations enable the visualization of concentration heterogeneity and spatially resolve the interfacial chemical states over a statistically significant field of view for buried interfaces. We report that concentration and chemical heterogeneities prevail at electrode|electrolyte interfaces, leading to phase separation in polymer electrolytes. In conclusion, understanding the hidden roles of interfacial chemomechanics in polymer electrolytes enables us to design an interphase tailoring strategy based on electrolyte additives to mitigate the interfacial heterogeneity and improve battery performance.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Deuterium incorporation into cellulose: a mini-review of biological and chemical methods

Isotopic enrichment offers structural insights that are not easily accessible with natural abundance isotopic composition. Deuterated cellulose has attracted considerable attention in the field of neutron scattering studies, providing information about the dynamics, structure of cellulose and its interactions with other plant cell wall components. The deuteration of cellulose also allows the analysis of cellulose hydrogen bonds by FTIR or NMR techniques. The chemical structure of cellulose contains both exchangeable hydroxyl and non-exchangeable alkyl hydrogens. Deuterium incorporation can be divided into two classifications: biological route which incorporates both alkyl and hydroxyl bound deuterium, and chemical route which typically replaces hydroxyl-bound exchangeable hydrogen. Additionally, the biological route involves cultivating plants or microorganisms in a deuterium-enriched medium. The chemical route typically involves an exchange reaction between hydroxyl-bound hydrogen and D 2 O, often facilitating with an alkaline reagent. This review provides an overview of recent advances in deuteration methods and characterization as well as the application of deuterated cellulose.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Synthesis of Mo 4 VAlC 4 MAX Phase and Two-Dimensional Mo 4 VC 4 MXene with Five Atomic Layers of Transition Metals

MXenes are a family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides with a general formula of M n+1 X n T x , in which two, three, or four atomic layers of a transition metal (M: Ti, Nb, V, Cr, Mo, Ta, etc.) are interleaved with layers of C and/or N (shown as X), and T x represents surface termination groups such as –OH, =O, and –F. Here, we report the scalable synthesis and characterization of a MXene with five atomic layers of transition metals (Mo 4 VC 4 T x ), by synthesizing its Mo 4 VAlC 4 MAX phase precursor that contains no other MAX phase impurities. These phases display twinning at their central M layers which is not present in any other known MAX phases or MXenes. Transmission electron microscopy and X-ray diffraction were used to examine the structure of both phases. Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy were used to study the composition of these materials. Density functional theory calculations indicate that other five transition metal-layer MAX phases (M' 4 M"AlC 4 ) may be possible, where M' and M" are two different transition metals. The predicted existence of additional Al-containing MAX phases suggests that more M 5 C 4 T x MXenes can be synthesized. Additionally, we characterized the optical, electronic, and thermal properties of Mo 4 VC 4 T x . Here, this study demonstrates the existence of an additional subfamily of M 5 X 4 T x MXenes as well as a twinned structure, allowing for a wider range of 2D structures and compositions for more control over properties, which could lead to many different applications.

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

Photoelectrochemical materials for solar energy conversion

Research and development on semiconductors for applications in solar energy conversion has witnessed rapid growth over the past several decades. With the aim of producing chemical fuels from sunlight, intense research efforts have focused on the discovery of semiconductors with crystalline structures and chemical compositions that have the potential to satisfy the complex set of required photoelectrochemical properties. This chapter focuses on the foundational structure-property relationships of selected oxide and nitride semiconductors relevant to their uses as n-/p-type photoelectrodes and as photocatalysts. Their solid-state structures and compositions are described, with a special emphasis on strategies proven effective at targeting suitable band gaps with strong visible-light absorption, efficient charge separation and diffusion of charge carriers, and optimal band edge energies for driving surface redox reactions for water splitting.

O’Donnell, Shaun↗
DOE OSTI2020

Understanding Charge Storage in Hydrated Layered Solids MOPO 4 (M = V, Nb) with Tunable Interlayer Chemistry

Hydrated layered solids are interesting charge storage hosts with potentially high electrochemical activity and interlayer tunability. Although it is often possible to tune their interlayer distance by a pillaring strategy, the poor electrochemical stability of such artificial structures remains a major issue in device operation. Here we investigate the charge storage properties of MOPO 4 (M = V, Nb) hydrates with a nanosheet morphology to understand the influence of the interlayer environment on cycling stability, as well as ion selectivity. While in hydrated VOPO 4 interlayer H 2 O molecules act as compressible springs to enable fast Li-/Na-ion transport kinetics and reasonable structural reversibility, NbOPO 4 layers with bridging PO 4 groups serving as permanent linkers exhibit highly stable cyclability for Li-ions, owing to a zero-volume-change ion transport process. However, the latter suffers from a much larger migration energy barrier for Na-ions. Lastly, our findings not only highlight a structurally intriguing material system, but also provide insights into reviving materials with an originally unstable interlayer chemical environment, and shed light on the design principles for creating electrochemically stable charge storage hosts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Synthesis and Properties of Bulk Mg 3 WN 4 in a Wurtzite-Derived Structure

Experimental synthesis of theoretically predicted materials with controlled elemental coordination environments can lead to the realization of useful properties, such as facile ion transport or ferroelectric switching. Among such materials are ternary nitrides in the Mg−W−N composition space, where several stable and metastable compounds have been predicted and synthesized recently in bulk and film forms. Here, we report for the first time on the bulk synthesis of Mg 3 WN 4 in a wurtzite-derived crystal structure via a solid-state metathesis reaction. In situ synchrotron powder X-ray diffraction shows how the ion exchange proceeds from Li 6 WN 4 + MgCl 2 precursors to Mg 3 WN 4 + LiCl products, with the reaction starting slowly near 380 °C and completing by 600 °C, including the presence of a competing disordered rocksalt-derived phase (Mg,W)N above 440 °C. The follow-up ex situ powder synthesis at 400 °C for 0.5 h with 10% excess MgCl 2 reveals the cation-ordered nature of the wurtzite-derived Mg 3 WN 4 structure with polar symmetry confirmed by second-harmonic generation measurements. Optical absorption spectra, chemical composition analysis, and electron microscopy imaging suggest that bulk Mg 3 WN 4 obtained via metathesis reaction is prone to defect formation. Overall, this study shows that selective ex situ synthesis of the phase-pure ternary nitrides, informed by in situ measurements, is possible by carefully controlling the thermal budget of the reaction and paves the way toward property characterization of the Mg 3 WN 4 wurtzite-derived material.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Moisture-Induced Structural Degradation in Methylammonium Lead Iodide Perovskite Thin Films

Methylammonium lead iodide (CH 3 NH 3 PbI 3 , MAPbI 3 ) belongs to the group of organic–inorganic halide perovskites (OIHPs) that exhibit exceptional electrical and optical behavior suitable for photovoltaic applications. However, improving its structural and chemical stability and robustness remains a challenge for OIHPs to be considered a feasible active material in optoelectronic devices. This is due to the fact that this material is very susceptible to degrade under various intrinsic and extrinsic factors. Therefore, it is crucial to understand the mechanisms through which MAPbI 3 undergoes chemical degradation under operating conditions such as a relatively humid environment. We present the structural characteristics of MAPbI 3 under working conditions that suggest the routes of phase segregation as a result of exposing to highly moist media. We use dark pulse discharge behavior and current–voltage (I–V) variations of MAPbI 3 under different moisture levels to investigate the nature of structural degradation in OIHPs. Here we show that while relatively lower levels of humidity (~60% RH) have a limited impact on the structural stability of MAPbI 3 , exposure to higher levels of moisture (~100% RH) results in the formation of PbI 2 and aqueous CH 3 NH 3 I, which fundamentally change the charge transport characteristics in MAPbI 3 . Our findings explain the ongoing debate on the presence of a threshold for the humidity that triggers irreversible structural transformation and leads to full degradation of MAPbI 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2024

The surface chemistry of the atomic layer deposition of metal thin films

Abstract In this perspective we discuss the progress made in the mechanistic studies of the surface chemistry associated with the atomic layer deposition (ALD) of metal films and the usefulness of that knowledge for the optimization of existing film growth processes and for the design of new ones. Our focus is on the deposition of late transition metals. We start by introducing some of the main surface-sensitive techniques and approaches used in this research. We comment on the general nature of the metallorganic complexes used as precursors for these depositions, and the uniqueness that solid surfaces and the absence of liquid solvents bring to the ALD chemistry and differentiate it from what is known from metalorganic chemistry in solution. We then delve into the adsorption and thermal chemistry of those precursors, highlighting the complex and stepwise nature of the decomposition of the organic ligands that usually ensued upon their thermal activation. We discuss the criteria relevant for the selection of co-reactants to be used on the second half of the ALD cycle, with emphasis on the redox chemistry often associated with the growth of metallic films starting from complexes with metal cations. Additional considerations include the nature of the substrate and the final structural and chemical properties of the growing films, which we indicate rarely retain the homogeneous 2D structure often aimed for. We end with some general conclusions and personal thoughts about the future of this field.

Materials Science↗
NASA NTRS2003

Common 5S rRNA variants are likely to be accepted in many sequence contexts

Over evolutionary time RNA sequences which are successfully fixed in a population are selected from among those that satisfy the structural and chemical requirements imposed by the function of the RNA. These sequences together comprise the structure space of the RNA. In principle, a comprehensive understanding of RNA structure and function would make it possible to enumerate which specific RNA sequences belong to a particular structure space and which do not. We are using bacterial 5S rRNA as a model system to attempt to identify principles that can be used to predict which sequences do or do not belong to the 5S rRNA structure space. One promising idea is the very intuitive notion that frequently seen sequence changes in an aligned data set of naturally occurring 5S rRNAs would be widely accepted in many other 5S rRNA sequence contexts. To test this hypothesis, we first developed well-defined operational definitions for a Vibrio region of the 5S rRNA structure space and what is meant by a highly variable position. Fourteen sequence variants (10 point changes and 4 base-pair changes) were identified in this way, which, by the hypothesis, would be expected to incorporate successfully in any of the known sequences in the Vibrio region. All 14 of these changes were constructed and separately introduced into the Vibrio proteolyticus 5S rRNA sequence where they are not normally found. Each variant was evaluated for its ability to function as a valid 5S rRNA in an E. coli cellular context. It was found that 93% (13/14) of the variants tested are likely valid 5S rRNAs in this context. In addition, seven variants were constructed that, although present in the Vibrio region, did not meet the stringent criteria for a highly variable position. In this case, 86% (6/7) are likely valid. As a control we also examined seven variants that are seldom or never seen in the Vibrio region of 5S rRNA sequence space. In this case only two of seven were found to be potentially valid. The results demonstrate that changes that occur multiple times in a local region of RNA sequence space in fact usually will be accepted in any sequence context in that same local region.

NASA Discipline Exobiology↗
DOE OSTI2021

Simultaneous ambient pressure x-ray photoelectron spectroscopy and grazing incidence x-ray scattering in gas environments

We have developed an experimental system to simultaneously measure surface structure, morphology, composition, chemical state, and chemical activity for samples in gas phase environments. This is accomplished by simultaneously measuring x-ray photoelectron spectroscopy (XPS) and grazing incidence x-ray scattering in gas pressures as high as the multi-Torr regime while also recording mass spectrometry. Scattering patterns reflect near-surface sample structures from the nano-scale to the meso-scale, and the grazing incidence geometry provides tunable depth sensitivity of structural measurements. Scattered x rays are detected across a broad range of angles using a newly designed pivoting-UHV-manipulator for detector positioning. At the same time, XPS and mass spectrometry can be measured, all from the same sample spot and under ambient conditions. To demonstrate the capabilities of this system, we measured the chemical state, composition, and structure of Ag-behenate on a Si(001) wafer in vacuum and in O 2 atmosphere at various temperatures. These simultaneous structural, chemical, and gas phase product probes enable detailed insights into the interplay between the structure and chemical state for samples in gas phase environments. The compact size of our pivoting-UHV-manipulator makes it possible to retrofit this technique into existing spectroscopic instruments installed at synchrotron beamlines. Because many synchrotron facilities are planning or undergoing upgrades to diffraction limited storage rings with transversely coherent beams, a newly emerging set of coherent x-ray scattering experiments can greatly benefit from the concepts we present here.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Electrochemical Oxidation in Garnet-Type Solid Electrolyte by Formation of Point Defects

All-solid-state batteries hold greater promise for improving safety and energy density over conventional battery technology employing organic liquid electrolytes. One of the required features of a Li + conducting solid electrolyte is electrochemical stability, attained thermodynamically or kinetically, within the targeted operating voltage and temperature ranges. Therefore, understanding of the oxidative or reductive degradation mechanism is important to allow the design of stable solid electrolyte materials. This work contributes to building an understanding of the oxidative degradation mechanism in lithium solid electrolytes at cell operating conditions. Here, we have focused on resolving the oxidative decomposition mechanism of Al-doped lithium garnet Li 6.28 Al 0.24 La 3 Zr 2 O 12 (LLZO) as a state-of-the-art inorganic ceramic electrolyte. By combining experimental and computational analyses, we show that oxidation of LLZO occurs by simultaneous loss of oxygen and lithium from the structure, resulting in substoichiometric LLZO, at a moderate temperature (80 °C) and a high electrode potential (4.3 V vs Li/Li + ). Based on X-ray absorption and diffraction analyses, we find that the zirconium coordination shells in LLZO contract while the crystal structure experiences positive chemical strain upon electrochemical oxidation. The results from ex situ structural characterization of both the local structure and crystal symmetry are supported by a substoichiometric LLZO with lithium and oxygen vacancies, modeled by density functional theory (DFT) calculations. These chemical and structural changes in LLZO suppress effective lithium-ion conductivity by an order of magnitude. Formation of lithium and oxygen vacancies in LLZO upon electrochemical oxidation is different from prior thermodynamic predictions of phase decomposition of LLZO. The difference here is that the experiments were conducted at near-room temperature, which can hinder the kinetics of phase separation, and thus, the resultant LLZO solid electrolyte is still single-phase but substoichiometric in Li and O. In conclusion, these findings contribute an important degradation mechanism of the electrolyte, relevant for practical operational conditions of solid-state batteries.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Accessing Atomic-scale Phosphorus Dopant Distribution in Precise Silicon Devices by Advanced STEM Imaging and Spectroscopy

The structural and chemical characterization at the atomic-scale plays a critical role in understanding the structure-property relationship in precise electrical devices such as those produced by atomic-precision advanced manufacturing (APAM). APAM, utilizing hydrogen lithography in a scanning tunneling microscope, offers a potential pathway to ultra-efficient transistors, and has been developed to produce phosphorus (P)-based donor devices integrated into bare Si substrates. Structural characterization of the buried, Si with P dopant (Si:P) delta-layer in the devices by scanning transmission electron microscopy (STEM), however, is a challenge due to similar atomic number and low concentration of the P dopants. In this paper, we describe several efforts of utilizing advanced STEM imagining and spectroscopic techniques to quantify the Si:P deltalayers. STEM imaging combining low-angle and high-angle annular dark-field (LAADF, HAADF) detectors as well as atomic-scale elemental mapping using energy-dispersive X-ray spectroscopy (EDS) are used to reveal the P and defect distribution across the delta-layer processed under various thermal conditions.

47 OTHER INSTRUMENTATION↗