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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Pressure‐Induced Structural and Magnetic Evolution in Layered Antiferromagnet YbMn 2 Sb 2

Electronic states under pressure exhibit unconventional spin and charge dynamics that provide a powerful route to uncover exotic phases in quantum materials. Here, we present the structural, magnetic, and electronic evolution of YbMn 2 Sb 2 under pressure. Single-crystal X-ray diffraction reveals a pressure-induced structural transition from the space group trigonal P$\overline{3}$m1 to the monoclinic P2 1 /m phase near 3.5 GPa, which remains stable up to 10 GPa. Magnetization measurements display an anomalously weak net magnetic moment and the absence of Curie–Weiss behavior up to 400 K, suggesting the formation of short-range Mn moment pairs that cancel macroscopically and subsequently evolve into long-range order upon cooling. Temperature-dependent resistivity shows semiconducting behavior with a transition at ∼119 K at ambient pressure, while pressure induces a dramatic suppression of resistance and the emergence of metallic-like temperature dependence, stabilized beyond 5 GPa. This pressure-driven semiconductor-metal transition is consistent with our density functional theory calculations, confirming the closing of the band gap under compression. Neutron diffraction under pressure identifies an incommensurate magnetic structure with antiparallel correlations between paired spins. Together, these results demonstrate how pressure-driven structural tuning and competing exchange interactions stabilize unconventional magnetic states in this low-dimensional magnetic semiconductor.

antiferromagnetic semiconductor↗
NASA NTRS1986

Wall turbulence control

A variety of wall turbulence control devices which were experimentally investigated are discussed; these include devices for burst control, alteration of outer flow structures, large eddy substitution, increased heat transfer efficiency, and reduction of wall pressure fluctuations. Control of pre-burst flow was demonstrated with a single, traveling surface depression which is phase-locked to elements of the burst production process. Another approach to wall turbulence control is to interfere with the outer layer coherent structures. A device in the outer part of a boundary layer was shown to suppress turbulence and reduce drag by opposing both the mean and unsteady vorticity in the boundary layer. Large eddy substitution is a method in which streamline curvature is introduced into the boundary layer in the form of streamwise vortices. Riblets, which were already shown to reduce turbulent drag, were also shown to exhibit superior heat transfer characteristics. Heat transfer efficiency as measured by the Reynolds Analogy Factor was shown to be as much as 36 percent greater than a smooth flat plate in a turbulent boundary layer. Large Eddy Break-Up (LEBU) which are also known to reduce turbulent drag were shown to reduce turbulent wall pressure fluctuation.

Wilkinson, Stephen P.↗
DOE OSTI2019

Dimensionally driven crossover from semimetal to direct semiconductor in layered SbAs

Two-dimensional (2D) materials have attracted a great deal of attention because they exhibit intriguing physical and chemical properties with great potential applications in electronic and optoelectronic devices, and even energy conversion. Due to the high anisotropy and unique crystal structure of layered materials, the properties can be effectively tuned by simply reducing dimensions to 2D. In this work, a unique 2D semiconductor, namely, monolayered SbAs, with high stability and indirect band gap, is predicted on the basis of first-principles calculations together with cluster expansion and Monte Carlo simulations. Interestingly, although the bulk antimony arsenide compound SbAs is known to exhibit semimetallic behavior, our calculations find that it is transformed into a direct semiconductor with a band gap of 1.28 eV when thinned down to a single atomic layer. The monolayer with antisite defects is transformed from indirect into a direct band-gap semiconductor. Such dramatic changes in the electronic structure could pave the way for SbAs to play a role in electronic device applications. Moreover, we find that the interlayer interactions in SbAs lead to a higher exfoliation energy than typical transition metal dichalcogenides such as MoS 2 , and hence we suggest that chemical deposition methods might be better than mechanical exfoliation methods for obtaining monolayer samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Growth and Characterization of Multi-Layer NbTiN Films

Significant theoretical interest has stimulated efforts to grow and characterize thin multi-layer superconductor/insulator/superconductor structures for their potential capability of supporting otherwise inaccessible surface magnetic fields in SRF cavities. The technological challenges include realization of high quality superconductors with sharp, clean, transition to high quality dielectric materials and back to superconductor, with careful thickness control of each layer. Choosing NbTiN as the first candidate material, we have developed the tools and techniques that produce such SIS film structures and have begun their characterization. Using DC magnetron sputtering and HiPIMS, NbTiN and AlN can be deposited with nominal superconducting and dielectric parameters. Hc1 enhancement is observed for NbTiN layers with a Tc of 16.9 K for a thickness less than 150 nm. The optimization of the thickness of each type of layer to reach optimum SRF performance is underway. This talk describes this work and the rf performance characteristics observed to date.

Valente-Feliciano, Anne-Marie↗
DOE OSTI2019

High Resolution Multimodal Chemical Imaging Platform for Organics and Inorganics

Chemical analysis at the nanoscale is critical to advance our understanding of materials and systems from medicine and biology to material science and computing. Macroscale-observed phenomena in these systems are in the large part driven by processes that take place at the nanoscale and are highly heterogeneous. Therefore, there is a clear need to develop a new technology that enables correlative imaging of material functionalities with nanoscale spatial and chemical resolutions that will enable us to untangle the structure–function relationship of functional materials. As such, here, we report on the analytical figures of merit of the newly developed correlative chemical imaging technique of helium ion microscopy coupled with secondary ion mass spectrometry (HIM-SIMS) that enables multimodal topographical/chemical imaging of organic and inorganic materials at the nanoscale. In HIM-SIMS, a focused ion beam acts as a sputtering and ionization source for chemical analysis along with simultaneous high-resolution surface imaging, providing an unprecedented level of spatial resolution for gathering chemical information on organic and inorganic materials. In this work, we demonstrate HIM-SIMS as a platform for a next-generation tool for an in situ material design and analysis capable of down to 8 nm spatial resolution chemical imaging, layered metal structure imaging in depth profiling, single graphene layer detection, and spectral analysis of metals, metal oxides, and polymers.

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

Porous but Mechanically Robust All-Inorganic Antireflective Coatings Synthesized using Polymers of Intrinsic Microporosity

Herein, we introduce polymer of intrinsic microporosity 1 (PIM-1) to design single-layer and multilayered all-inorganic antireflective coatings (ARCs) with excellent mechanical properties. Using PIM-1 as a template in sequential infiltration synthesis (SIS), we can fabricate highly uniform, mechanically stable conformal coatings of AlO x with porosities of ~50% and a refractive index of 1.41 compared to 1.76 for nonporous AlO x that is perfectly suited for substrates commonly used in high-end optical systems or touch screens (e.g., sapphire, conductive glass, bendable glass, etc.). We show that such films can be used as a single-layer ARC capable of reduction of the Fresnel reflections of sapphire to as low as 0.1% at 500 nm being deposited only on one side of the substrate. We also demonstrate that deposition of the second layer with higher porosity using block copolymers enables the design of graded-index double-layered coatings. AlO x structures with just two layers and a total thickness of less than 200 nm are capable of reduction of Fresnel reflections under normal illumination to below 0.5% in a broad spectral range with 0.1% reflection at 700 nm. Additionally, and most importantly, we show that highly porous single-layer and graded-index double-layered ARCs are characterized by high hardness and scratch resistivity. The hardness and the maximum reached load were 7.5 GPa and 13 mN with a scratch depth of about 130 nm, respectively, that is very promising for the structures consisting of two porous AlO x layers with 50% and 85% porosities, correspondingly. Such mechanical properties of coatings can also allow their application as protective layers for other optical coatings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Characterization of structural response to hypersonic boundary-layer transition

The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and they can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.

42 ENGINEERING↗
DOE OSTI2018

Creating Zipper‐Like van der Waals Gap Discontinuity in Low‐Temperature‐Processed Nanostructured PbBi 2 n Te 1+3 n : Enhanced Phonon Scattering and Improved Thermoelectric Performance

Abstract Nanoengineered materials can embody distinct atomic structures which deviate from that of the bulk‐grain counterpart and induce significantly modified electronic structures and physical/chemical properties. The phonon structure and thermal properties, which can also be potentially modulated by the modified atomic structure in nanostructured materials, however, are seldom investigated. Employed here is a mild approach to fabricate nanostructured PbBi 2 n Te 1+3 n using a solution‐synthesized PbTe‐Bi 2 Te 3 nano‐heterostructure as a precursor. The as‐obtained monoliths have unprecedented atomic structure, differing from that of the bulk counterpart, especially the zipper‐like van der Waals gap discontinuity and the random arrangement of septuple‐quintuple layers. These structural motifs break the lattice periodicity and coherence of phonon transport, leading to ultralow thermal conductivity and excellent thermoelectric z T .

Xu, Biao↗
DOE OSTI2019

Pressure effect on the electronic, structural, and vibrational properties of layered 2 H - MoTe 2

Layered molybdenum dichalchogenides differ from the classic example of bilayer graphene with their unique electronic properties: the application of pressure can continuously tune electronic structure since the band gap is controlled by delicate interlayer interaction. In this work, we have performed measurements of Raman scattering, synchrotron x-ray diffraction, electrical conductivity, and Hall coefficient combined with density functional theory calculations to synthetically study the pressure effect on $2H$-MoTe 2 . Both the experiments and calculations consistently demonstrate that MoTe2 undergoes a semiconductor-to-metallic (S-M) transition above 10 GPa. Unlike MoS 2 , the S-M transition is driven by the gradual tunability of electric structure and band gap without structural transition. The applied pressure also effectively enhances conductivity and carrier concentration while reducing the mobility, which makes MoTe 2 more suitable for applications than most other transition-metal dichalchogenides and allows it to be applied in strain-modulated optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Study on Application of Geopolymer to the Retrieval of Fuel Debris in Fukushima Dai-ichi NPP

In order to retrieve fuel debris in Fukushima Dai-ichi NPP, many retrieval methods are proposed. Geopolymer is the candidate material applied for an alternative retrieval method. In this concept, Geopolymer can be used to stabilize fuel debris and suppress the diffusion of radioactive materials. Objective: Evaluation of geopolymer applied for retrieving fuel debris. Slump Flow Test: Slump flow values decreased as the test temperature increased. In air condition, water molecules evaporated from geopolymer and the viscosity of geopolymer increased. In water condition, the same trends as in air condition were observed. Slump flow values of geopolymer also depended on the elapsed time after mixing. By adding water, the slump flow values of geopolymer became higher (Even at 80 deg. C). It is possible to adjust the solidification time (Setting time) of geopolymer. Solidification Process of Geopolymer: After the first layer solidified, the second layer was injected. At 300 deg. C, porous structure was observed in the first layer, while the second layer structure was intact. In the actual application, multilayered geopolymer may be used to stabilize fuel debris. Conclusion: Fluidity of geopolymer decreased with raising temperature. Setting time can be adjusted by adding water. Geopolymer may be applied by injecting multiple times on high temperature materials above 100 deg. C.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Integral analysis of the effect of material dimension and composition on tokamak neutronics *

Abstract The neutronics performance of a tokamak has been identified as an important factor in designing a fusion power plant. The design of the tokamak should not only meet operational parameters such as sufficient tritium breeding, but also safety parameters such as low structural material activation. This paper investigates the impacts of the neutronics metrics for the ARC-class tokamak, a compact tokamak with an immersion blanket, by perturbing the first five layers of structural material—first wall, inner vacuum vessel, coolant salt channel, neutron multiplier, and outer vacuum vessel. The goal of this work is to provide insight into shaping and scaling the flux on each layer to obtain optimized operational and safety metrics through quantification of the responses from each perturbation. Results show that increased first wall thickness can increase the tritium breeding ratio (TBR) in specific configurations with high 6 Li enrichments and that vacuum vessels decrease TBR for low- 6 Li enrichment configurations. It was also found that the neutron multiplier can either increase or decrease TBR depending on the configuration. The response of metrics to the change in layer thickness and enrichment also varies depending on the vacuum vessel material. The integral impacts of 6 Li enrichment, layer thicknesses, and vacuum vessel material choice are investigated and presented in this paper.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1998

Microstructural, Chemical and Mechanical Characterization of Polymer-Derived Hi-Nicalon Fibers with Surface Coatings

Room temperature tensile strengths of as-received Hi-Nicalon fibers and those having BN/SiC, p-BN/SiC, and p-B(Si)N/SiC surface coatings, deposited by chemical vapor deposition, were measured using an average fiber diameter of 13.5 microns. The Weibull statistical parameters were determined for each fiber. The average tensile strength of uncoated Hi-Nicalon on was 3.19 +/- 0.73 GPa with a Weibull modulus of 5.41. Strength of fibers coated with BN/SiC did not change. However, coat with p-BN/SiC and p-B(Si)N/SiC surface layers showed strength loss of approx. 10 and 35 percent, respectively, compared with as-received fibers. The elemental compositions of the fibers and the coatings were analyzed using scanning Auger microprobe and energy dispersive x-ray spectroscopy. The BN coating was contaminated with a large concentration of carbon and some oxygen. In contrast, p-BN, p-B(Si)N, and SiC coatings did not show any contamination. Microstructural analyses of the fibers and the coatings were done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction. Hi-Nicalon fiber consists of the P-SIC nanocrystals ranging in size from 1 to 30 nm embedded in an amorphous matrix. TEM analysis of the BN coating revealed four distinct layers with turbostatic structure. The p-BN layer was turbostratic and showed considerable preferred orientation. The p-B(Si)N was glassy and the silicon and boron were uniformly distributed. The silicon carbide coating was polycrystalline with a columnar structure along the growth direction. The p-B(Si)N/SiC coatings were more uniform, less defective and of better quality than the BN/SiC or the p-BN/SiC coatings.

Bansal, Narottam P.↗
DOE OSTI2022

Regulation of Surface Defect Chemistry toward Stable Ni-Rich Cathodes

Surface reconstruction of Ni-rich layered oxides (NLO) degrades the cycling stability and safety of high-energy-density lithium-ion batteries (LIBs), which challenges typical surface-modification approaches to build a robust interface with electrochemical activity. Here, a strategy of leveraging the low-strain analogues of Li- and Mn-rich layered oxides (LMR) to reconstruct a stable surface on the Ni-rich layered cathodes is proposed. The new surface structure not only consists of a gradient chemical composition but also contains a defect-rich structure regarding the formation of oxygen vacancies and cationic ordering, which can simultaneously facilitate lithium diffusion and stabilize the crystal structure during the (de)lithiation. These features in the NLO lead to a dramatic improvement in electrochemical properties, especially the cyclability under high voltage cycling, exhibiting the 30% increase in capacity retention after 200 cycles at the current density of 1 C (3.0-4.6 V). We report the findings offer a facile and effective way to regulate defect chemistry and surface structure in parallel on Ni-rich layered structure cathodes to achieve high-energy density LIBs.

25 ENERGY STORAGE↗
DOE OSTI2019

Collapse of LiNi 1– x–y Co x Mn y O 2 Lattice at Deep Charge Irrespective of Nickel Content in Lithium-Ion Batteries

Volume variation and the associated mechanical fracture of electrode materials upon Li extraction/insertion are a main cause limiting lifetime performance of lithium-ion batteries. For LiNi 1-x-y Co x Mn y O 2 (NCM) cathodes, abrupt anisotropic collapse of the layered lattice structure at deep charge is generally considered characteristic to high Ni content and can be effectively suppressed by elemental substitution. Herein, we demonstrate the lattice collapse is a universal phenomenon almost entirely dependent on Li utilization, and not Ni content, of NCM cathodes upon delithiation. With Li removal nearing 80 mol%, very similar c-axis lattice shrinkage of around 5% occurs concurrently for NCMs synthesized in-house regardless of nickel content (90, 70, 50, or 33 mol%); meanwhile, the a-axis lattice contracts for high-Ni NCM, but it expands for low-Ni NCM. We further reveal Co-Mn co-substitution in NCM barely, if at all, affects several key structural aspects governing the lattice distortion upon delithiation. Finally, our results highlight the importance of evaluating true implications of compositional tuning on high-Ni layered oxide cathode materials to maximize their charge-storage capacities for next-generation high-energy Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2018

Traditional Semiconductors in the Two-Dimensional Limit

Interest in two-dimensional materials has exploded in recent years. Not only are they studied due to their novel electronic properties, such as the emergent Dirac fermion in graphene, but also as a new paradigm in which stacking layers of distinct two-dimensional materials may enable different functionality or devices. Here, through first-principles theory, we reveal a large new class of two-dimensional materials which are derived from traditional III-V, II-VI, and I-VII semiconductors. It is found that in the ultrathin limit the great majority of traditional binary semiconductors studied (a series of 28 semiconductors) are not only kinetically stable in a two-dimensional double layer honeycomb structure, but more energetically stable than the truncated wurtzite or zinc-blende structures associated with three dimensional bulk. These findings both greatly increase the landscape of two-dimensional materials and also demonstrate that in the double layer honeycomb form, even ordinary semiconductors, such as GaAs, can exhibit exotic topological properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1977

Extraction of the large eddy structure of a turbulent boundary layer

Much attention is currently being focused on turbulence modeling by separation of large-scale and small-scale turbulence. One major difficulty with this method is the problem of separating and defining the large-scale structure. In this paper, a method is presented which does this separation by analyzing time-averaged, two-point double velocity correlation measurements. The basis of the method is a maximization of the inner product of a candidate velocity field with the measured turbulent velocity field. An eigenvalue problem results, whose solution provides a set of orthogonal eigenfunctions associated with specific modes of turbulent motion. The large-scale eddy, containing most of the turbulent energy, is associated with the first (largest) mode. The turbulent velocity field is then represented as a sum of the eigenfunctions. A short description of the equations is given, the methods of solution are discussed, and some results for a two-dimensional fully developed turbulent boundary layer are presented.

Lemmerman, L. A.↗
NASA NTRS2015

Environmental Effects on Long Term Displacement Data of Woven Fabric Webbings Under Constant Load for Inflatable Structures

An experimental study of the effects of environmental temperature and humidity conditions on long-term creep displacement data of high strength Kevlar and VectranTM woven fabric webbings under constant load for inflatable structures is presented. The restraint layer of an inflatable structure for long-duration space exploration missions is designed to bear load and consists of an assembly of high strength webbings. Long-term creep displacement data of webbings can be utilized by designers to validate service life parameters of restraint layers of inflatable structures. Five groups of high-strength webbings were researched over a two year period. Each group had a unique webbing length, load rating, applied load, and test period. The five groups consisted of 1.) 6K Vectran webbings loaded to 49% ultimate tensile strength (UTS), 2.) 6K Vectran webbings loaded to 55% UTS, 3.) 12.5K Vectran webbings loaded to 22% UTS, 4.) 6K Kevlar webbings loaded to 40% and 43% UTS, and 5.) 6K Kevlar webbings loaded to 48% UTS. Results show that all webbing groups exhibit the initial two stages of three of a typical creep curve of an elastic material. Results also show that webbings exhibit unique local wave patterns over the duration of the test period. Data indicate that the local pattern is primarily generated by daily variations in relative humidity values within the test facility. Data indicate that after a three to six month period, where webbings reach a steady-state creep condition, an annual sinusoidal displacement pattern is exhibited, primarily due to variations in annual mean temperature values. Data indicates that variations in daily temperature values and annual mean humidity values have limited secondary effects on creep displacement behavior. Results show that webbings in groups 2 and 5 do not exhibit well defined annual displacement patterns because the magnitude of the applied loads cause large deformations, and data indicate that material yielding within a webbing tends to neutralize the annual sinusoidal displacement pattern. Study indicates that applied load, environmental effects, mechanical strength, coefficient of thermal expansion, and hygroscopic properties of webbings are fundamental requirements for quantifying accurate creep displacements and behaviors over multiple year time periods. Results from a study of the environmental effects on long-term creep displacement data of Kevlar and Vectran woven webbings are presented to increase the knowledge base of webbing materials and to enhance designs of inflatable space structures for long-duration space missions.

Kenner, WInfred S.↗