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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A study of degradation mechanisms in PVDF-based photovoltaic backsheets

Abstract Commercial backsheets based on polyvinylidene fluoride (PVDF) can experience premature field failures in the form of outer layer cracking. This work seeks to provide a better understanding of the changes in material properties that lead to crack formation and find appropriate accelerated tests to replicate them. The PVDF-based backsheet outer layer can have a different structure and composition, and is often blended with a poly(methyl methacrylate) (PMMA) polymer. We observed depletion of PMMA upon aging with sequential (MAST) and combined (C-AST) accelerated stress testing. In field-aged samples from Arizona and India, where PVDF crystallizes in its predominant α-phase, the degree of crystallinity greatly increased. MAST and C-AST protocols were, to some extent, able to replicate the increase in crystallinity seen in PVDF after ~ 7 years in the field, but no single-stress test condition (UV, damp heat, thermal cycling) resulted in significant changes in the material properties. The MAST regimen used here was too extreme to produce realistic degradation, but the test was useful in discovering weaknesses of the particular PVDF-based outer layer structure studied. No excessive β-phase formation was observed after aging with any test condition; however, the presence of β-phase was identified locally by Fourier transform infrared spectroscopy (FTIR). We conclude that both MAST and C-AST are relevant tests for screening outdoor failure mechanisms in PVDF backsheets, as they were successful in producing material degradation that led to cracking.

14 SOLAR ENERGY↗
NASA NTRS2005

Electric field measurements of DC and long wavelength structures associated with sporadic-E layers and QP radar echoes

Electric field and plasma density data gathered on a sounding rocket launched from Uchinoura Space Center, Japan, reveal a complex electrodynamics associated with sporadic-E layers and simultaneous observations of quasiperiodic radar echoes. The electrodynamics are characterized by spatial and temporal variations that differed considerably between the rocket's up-leg and down-leg traversals of the lower ionosphere. Within the main sporadic-E layer (95- 110 km) on the up-leg, the electric fields were variable, with amplitudes of 2 4 mV1m that changed considerably within altitude intervals of 1-3 km. The identification of polarization electric fields coinciding with plasma density enhancements and/or depletions is not readily apparent. Within this region on the down-leg, however, the direction of the electric field revealed a marked change that coincided precisely with the peak of a single, narrow sporadic-E plasma density layer near 102.5 km. This shear was presumably associated with the neutral wind shear responsible for the layer formation. The electric field data above the sporadic-E layer on the upleg, from 110 km to the rocket apogee of 152 km, revealed a continuous train of distinct, large scale, quasi-periodic structures with wavelengths of 10-15 km and wavevectors oriented between the NE-SW quadrants. The electric field structures had typical amplitudes of 3-5 mV/m with one excursion to 9mV/m, and in a very general sense, were associated with perturbations in the plasma density. The electric field waveforms showed evidence for steepening and/or convergence effects and presumably had mapped upwards along the magnetic field from the sporadic-E region below.

Pfaff, R.↗
DOE OSTI2020

Magnetic structure and exchange interactions in the layered semiconductor CrPS 4

Compounds with two-dimensional (2D) layers of magnetic ions weakly connected by van der Waals bonding offer routes to enhance quantum behavior, stimulating both fundamental and applied interest. CrPS 4 is one such magnetic van der Waals material, however, it has undergone only limited investigation. Here we present a comprehensive series of neutron scattering measurements to determine the magnetic structure and exchange interactions. The observed magnetic excitations allow a high degree of constraint on the model parameters not normally associated with measurements on a powder sample. The results demonstrate the 2D nature of the magnetic interactions, while also revealing the importance of interactions along 1D chains within the layers. The subtle role of competing interactions is observed, which manifest in a nontrivial magnetic transition and a tunable magnetic structure in a small applied magnetic field through a spin-flop transition. Our results on the bulk compound provide insights that can be applied to an understanding of the behavior of reduced layer CrPS 4 .

36 MATERIALS SCIENCE↗
NASA NTRS1976

Interplanetary boundary layers at 1 AU

The structure and nature of discontinuities in the interplanetary magnetic field at 1 AU in the period March 18, 1971 to April 9, 1971, is determined by using high-resolution magnetic field measurements from Explorer 34. The discontinuities that were selected for this analysis occurred under a variety of interplanetary conditions at an average rate of 0.5/hr. This set does not include all discontinuities that were present, but the sample is large and it is probably representative. Both tangential and rotational discontinuities were identified, the ratio of TD's to RD's being approximately 3 to 1. Tangential discontinuities were observed every day, even among Alfvenic fluctuations. The structure of most of the boundary layers was simple and ordered, i.e., the magnetic field usually changed smoothly and monotonically from one side of the boundary layer to the other.

Burlaga, L. F.↗
NASA NTRS1982

A New View on Origin, Role and Manipulation of Large Scales in Turbulent Boundary Layers

The potential of passive 'manipulators' for altering the large scale turbulent structures in boundary layers was investigated. Utilizing smoke wire visualization and multisensor probes, the experiment verified that the outer scales could be suppressed by simple arrangements of parallel plates. As a result of suppressing the outer scales in turbulent layers, a decrease in the streamwise growth of the boundary layer thickness was achieved and was coupled with a 30 percent decrease in the local wall friction coefficient. After accounting for the drag on the manipulator plates, the net drag reduction reached a value of 20 percent within 55 boundary layer thicknesses downstream of the device. No evidence for the reoccurrence of the outer scales was present at this streamwise distance thereby suggesting that further reductions in the net drag are attainable. The frequency of occurrence of the wall events is simultaneously dependent on the two parameters, Re2 delta sub 2 and Re sub x. As a result of being able to independently control the inner and outer boundary layer characteristics with these manipulators, a different view of these layers emerged.

Corke, T. C.↗
DOE OSTI2018

Influence of π-conjugated cations and halogen substitution on the optoelectronic and excitonic properties of layered hybrid perovskites

Low-cost chemical engineering of two-dimensional layered hybrid halide perovskite structures allows for the design of hybrid semiconductor quantum wells with tailored room-temperature excitonic optical absorption, emission, and charge carrier transport properties. Here density functional theory and the Bethe-Salpeter equation are used to predict the electronic structure and optical response of layered perovskites with two representative single-ring conjugated organic spacers, ammonium-propyl-imidazole (API) and 2-phenethylammonium (PEA). The inorganic perovskite quantum well properties are further tuned by analyzing the effect of halogen (X = I, Br, Cl) substitution. We found that visible light absorption occurs primarily within the perovskite layer and that UV light absorption induces partial electron-hole separation between layers. In addition, a strong exciton binding energy and influence on absorption spectrum is found by solving the Bethe-Salpeter equation. Our results suggest that further engineering is necessary beyond the single-ring limit, by introducing more conjugated rings and/or heavier nuclei into the organic spacer. This is a promising future direction to achieve photoinduced charge separation and more generally hybrid heterostructures with attractive optoelectronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Altermagnetism in the layered intercalated transition metal dichalcogenide CoNb 4 Se 8

Altermagnets (AMs) are a new class of magnetic materials that combine the beneficial spintronics properties of ferromagnets and antiferromagnets, garnering significant attention recently. Here, we have identified altermagnetism in a layered intercalated transition metal diselenide, CoNb 4 Se 8 , which crystallizes with an ordered sublattice of intercalated Co atoms between NbSe 2 layers. Single crystals are synthesized, and the structural characterizations are performed using single crystal diffraction and scanning tunneling microscopy. Magnetic measurements reveal easy-axis antiferromagnetism below 168 K. Density functional theory (DFT) calculations indicate that A-type antiferromagnetic ordering with easy-axis spin direction is the ground state, which is verified through single crystal neutron diffraction experiments. Electronic band structure calculations in this magnetic state display spin-split bands, confirming altermagnetism in this compound. The layered structure of CoNb 4 Se 8 presents a promising platform for testing various predicted properties associated with altermagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Temperature-Sensitive Structure Evolution of Lithium–Manganese-Rich Layered Oxides for Lithium-Ion Batteries

Cathodes of lithium-rich layered oxides for high-energy Li-ion batteries in electrically powered vehicles are attracting considerable attention by the research community. Furthermore, current research is insufficient to account for their complex reaction mechanism and application. Thus, the structural evolution of lithium-manganese-rich layered oxides at different temperatures during electrochemical cycling has been investigated thoroughly, and their structural stability has been designed. The results indicated structure conversion from the two structures into a core-shell structure with a single distorted-monoclinic LiTMO 2 structure core and disordered-spinel/rock salt structure shell, along with lattice oxygen extraction and lattice densification, transition- metal migration, and aggregation on the crystal surface. Here, the structural conversion behavior was found to be seriously temperature sensitive, accelerated with higher temperature, and can be effectively adjusted by structural design. This study clarifies the structural evolution mechanism of these lithium-rich layered oxides and opens the door to the design of similar high-energy materials with better cycle stability.

25 ENERGY STORAGE↗
DOE OSTI2017

Surface Reconstruction in Li-Rich Layered Oxides of Li-Ion Batteries

The performance characteristics of lithium-ion battery cathode materials are governed by the surface structure and chemistry. Synthesis is known to affect the structure of these materials; however, a full understanding of the effects of the surface structure is not well understood. Here, we explore the atomic scale structure of lithium-layered oxides prepared with two different thermal treatments. In this work we show that, under certain thermal treatments, the surface perpendicular to the transition-metal layers is enriched in nickel, which results in Ni occupying the lithium layer of the layered oxide structure. Under both thermal treatments, this surface also shows a reduction of Mn, with some of the reduced Mn occupying sites in the lithium layer. The surface parallel to the transition-metal layers under both treatments shows significant Mn reduction, oxygen loss, and reduced Mn in the lithium layer. The Mn reduction and surface reconstruction are the result of unstable surface terminations and are intrinsic to layered oxides. Synthesis can be tuned to eliminate Ni enrichment at the surface; however, it cannot be tailored to eliminate Mn reduction and surface reconstruction.

25 ENERGY STORAGE↗
DOE OSTI2022

Progress in three-terminal heterojunction bipolar transistor solar cells

Conventional solar cells, including multijunction solar cells, are based on pn junctions as building blocks. In contrast, the three-terminal heterojunction bipolar transistor solar cell (3T-HBTSC) explores the use of a bipolar transistor structure to build a solar cell. The limiting efficiency of this transistor structure equals that of a double-junction solar cell. However, since the 3T-HBTSC does not require tunnel junctions, its minimal structure has only three semiconductor layers, while the minimal structure of a double junction solar cell has six. This work reviews the operation principles of this solar cell and the steps carried out towards its practical implementation. Experimental results on a GaInP/GaAs HBTSC prototype with bottom interdigitated contacts are presented.

14 SOLAR ENERGY↗
DOE OSTI2025

Zr 3 Mn 3 Sn 4 Ga: A new hetero-kagome bilayer antiferromagnet

Here, we report the magnetic and electrical transport properties of single-crystalline Zr 3 Mn 3 Sn 4 Ga, featuring two distinct kagome lattices: a non-magnetic breathing Zr 3 Sn 4 lattice and a magnetic intact Mn 3 Ga lattice. The material undergoes an antiferromagnetic phase transition at T N = 87 K, with neutron diffraction confirming commensurate ordering characterized by k = (1/3,1/3,0). Transport measurements show metallic behavior, a resistivity anomaly near T N , and 12% magnetoresistance at 2 K under 9 T. Deviations from the conventional second-order power law, along with negative magnetoresistance and nonlinear Hall slope variations near T N , suggest strong magneto-electronic coupling. Resonant photoemission spectroscopy identifies Zr 4d and Mn 3d orbitals as dominant contributors to the valence band, linking the material’s unique electronic properties to its kagome layers. Zr 3 Mn 3 Sn 4 Ga offers a valuable platform to study interactions between magnetism and topological electronic bands in hetero-kagome systems using the co- existence of magnetic and non-magnetic kagome layers and its tunable electronic structure.

Crystal structure↗
NASA NTRS1974

Ion implanted epitaxially grown ZnSe

The epitaxial growth of ZnSe on (100) Ge using the close-spaced transport process is described. Substrate temperature of 575 C and source temperatures of 675 C yield 10 micron, single crystal layers in 10 hours. The Ge substrates provides a nonreplenishable chemical transport agent and the epitaxial layer thickness is limited to approximately 10 microns. Grown epitaxial layers show excellent photoluminescence structure at 77 K. Grown layers exhibit high resistivity, and annealing in Zn vapor at 575 C reduces the resistivity to 10-100 ohms-cm. Zinc vapor annealing quenches the visible photoluminescence.

Source record↗
NASA NTRS1992

A three-dimensional axisymmetric photochemical flow model of the cometary 'inner' shock layer

Assuming the Newtonian thin layer approximation to describe the structure of the shock layer between the cometary 'ionopause' and the inner shock, a 3D axisymmetric photochemical flow model of this layer is constructed. While sources of ions in this layer are the flow across the inner shock and photoionization of neutrals within it, the sinks are the flow into the flanks and dissociative recombination, the latter being the dominant one. For Halley's comet at the time of the Giotto encounter, the calculated thickness of the layer is very small, typically about 100 km for expected values of the dissociative-recombination coefficient. This is not inconsistent with the observations. The lateral flow speed near the point of encounter (inbound) is about 0.9 km/s, while the sonic line is at an angle of about 50 deg to the sun-comet line. Testing the validity of this model will have to await a cometary rendezvous mission such as the proposed CRAF/Cassini mission.

Damas, M. C.↗
DOE OSTI2025

Evolution of intermittent filaments in the scrape-off layer of NSTX

Filamentary structures naturally arise from background turbulence in the scrape-off layer (SOL) of plasmas, leading to significant particle and heat transport that can degrade overall plasma confinement. This enhanced transport can contribute to unacceptably high heat loads on plasma-facing components. As such, understanding the physics of SOL plasma filaments is critical for predicting and mitigating their effects in future fusion devices. On the National Spherical Torus Experiment (NSTX), plasma filaments—commonly referred to as “blobs”—were investigated using the gas-puff imaging (GPI) diagnostic in the edge and SOL regions. The analysis involved identifying, segmenting, and tracking the characteristic contours of the blobs in each frame of the GPI video sequences. Their evolution was characterized through shape descriptors, velocity, and angular velocity derived from their contour coordinates. The results indicate that as the blob area increases, their shapes become more concave and less circular, suggesting reduced structural stability in larger blobs. This result aligns with previous theoretical results where it was shown that larger blobs are more susceptible to instabilities [Krasheninnikov et al., J. Plasma Phys. 74, 679–717 (2008) and D'Ippolito et al., Phys. Plasmas 18, 060501 (2011)]. A positive correlation was observed between radial velocity and radial position, suggesting radially outward acceleration of the filaments, potentially driven by decreasing viscous drag toward the far SOL. Interestingly, blobs in background SOL turbulence exhibited minimal spinning in contrast to filaments originating from edge localized modes, which show substantial rotation during their paths [Lampert et al., Phys. Plasmas 29, 102502 (2022)]. Statistical analysis of the solidity and total curvature shape descriptors, along with their temporal evolution, revealed relatively broad, near-Gaussian distributions. This suggests that blob morphology is strongly influenced by stochastic turbulent processes in the surrounding plasma environment. Blob parameters were also compared with bulk plasma and radial profile measurements. Notable trends were found between blob rotation and poloidal velocity with collisionality and line-integrated density. These findings contribute to a deeper understanding of blob dynamics and provide valuable insights for refining SOL turbulence models.

Covariance and correlation↗
NASA NTRS2000

Thermally conductive support structure

A structure for supporting and at least transferring heat energy away from at least a first heat source interconnected thereto is disclosed. In one embodiment, the structure includes a deck member having a plurality of layers of thermally conductive fibers packed within a matrix material. Fibers of at least a first layer are orientable to transfer heat energy toward at least a first sidewall of the deck member, and fibers of at least a second layer are orientable about .+-.45.degree. relative to the fibers of the first layer to enhance the structural strength of the deck member. In another embodiment, fibers of at least a first layer of thermally conductive fibers of the deck member are orientable to transfer heat energy from a first heat source to a second, cooler heat source, both of which are interconnectable to the deck member, such that the first and second heat sources operate at substantially uniform temperatures. In this embodiment, fibers of at least a second layer of thermally conductive fibers are orientable about .+-.45.degree. relative to the fibers of the first layer to enhance the structural strength of the deck member. Fibers of at least a third layer of thermally conductive fibers are orientable substantially orthogonally relative to the fibers of the first layer to transfer heat energy away from at least the first heat source to at least a first sidewall of the deck member.

Herzl, Alfred↗
DOE OSTI2019

Probing Electrochemically Induced Structural Evolution and Oxygen Redox Reactions in Layered Lithium Iridate

In order to exploit electrochemical capacity beyond the traditionally-utilized transition metal redox reactions in lithium-metal-oxide cathode materials, it is necessary to understand the role that oxygen ions play in the charge compensation mech-anisms, i.e., to know the conditions triggering electron transfer on the oxygen ions and whether this transfer is correlated with battery capacity. Theoretical and experimental investigations of a model cathode material, Li-rich layered Li 2 IrO 3 , have been performed to study the structural and electronic changes induced by electrochemical delithiation in a lithium-ion cell. First-principles density functional theory (DFT) calculations were used to compute the voltage profile of a Li/Li 2-x IrO 3 cell at various states of charge, and the results were in good agreement with electrochemical data. Electron energy loss spectroscopy (EELS), X-ray absorption near-edge spectroscopy (XANES), resonant/non-resonant X-ray emission spectroscopy (XES), and first principles core-level spectra simulations using the Bethe Salpeter Equation (BSE) approach were used to probe the change in oxygen electronic states over the $x$ = 0 to 1.5 range. The correlated Ir M 3 -edge XANES and O K-edge XANES data provided evidence that oxygen hole states form during the early stage of delithiation at ~3.5 V due to the interaction between O $p$ and Ir $d$ states, with Ir oxidation being the dominant source of electrochemical capacity. At higher potentials, the charge capacity was predominantly attributed to oxidation of the O 2- ions. It is argued that the emergence of oxygen holes alone is not necessarily indicative of electrochemical capacity beyond transition metal oxidation, since oxygen hole states can appear as a result of enhanced mixing of O $p$ and Ir $d$ states. Prevailing mechanisms accounting for the oxygen redox mechanism in Li-rich materials were examined by theoretical and experimental X-ray spectroscopy; however, no unambiguous spectroscopic signatures of oxygen dimer interaction or non-bonding oxygen states were identified.

25 ENERGY STORAGE↗
NASA NTRS2002

Multidimensional indexing structure for use with linear optimization queries

Linear optimization queries, which usually arise in various decision support and resource planning applications, are queries that retrieve top N data records (where N is an integer greater than zero) which satisfy a specific optimization criterion. The optimization criterion is to either maximize or minimize a linear equation. The coefficients of the linear equation are given at query time. Methods and apparatus are disclosed for constructing, maintaining and utilizing a multidimensional indexing structure of database records to improve the execution speed of linear optimization queries. Database records with numerical attributes are organized into a number of layers and each layer represents a geometric structure called convex hull. Such linear optimization queries are processed by searching from the outer-most layer of this multi-layer indexing structure inwards. At least one record per layer will satisfy the query criterion and the number of layers needed to be searched depends on the spatial distribution of records, the query-issued linear coefficients, and N, the number of records to be returned. When N is small compared to the total size of the database, answering the query typically requires searching only a small fraction of all relevant records, resulting in a tremendous speedup as compared to linearly scanning the entire dataset.

Bergman, Lawrence David↗