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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Non-Equilibrium relaxation, aging scaling, and critical depinning dynamics of skyrmions in disordered magnetic films. Final Report

Technical applications of type-II superconductors, especially high-Tc compounds, in external magnetic fields require an effective flux pinning mechanism to reduce Ohmic losses due to flux creep and flow. Naturally abundant point defects, dislocations, and twin boundaries as well as artificially introduced disorder may serve as effective pinning centers for magnetic vortices. The properties of interacting flux lines subject to strong thermal fluctuations and point-like or extended pinning centers have therefore been a major research focus in condensed matter physics, and considerable progress has been achieved in the characterization and mathematical description of the equilibrium phases and non-equilibrium steady states of vortex matter. Detailed studies of the rich phase diagrams that reveal novel glassy states as well as the associated complex dynamical phenomena have in turn enriched the theoretical understanding of condensed matter systems, elucidating specifically the kinetics of elastic objects driven through disordered media and the important role of topological defects such as vortices and dislocations in various materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Miniaturized Hybrid Materials Inspired by Nature (Final Technical Report)

The objective of our research program is to develop a fundamental scientific understanding of assembly in biomolecular materials mediated by mechanisms that mimic complex events in the cellular environment. The building blocks that we study include globular, disordered, and filamentous proteins, lipids, and nucleic acids. Notably, the nanoscale assemblies may either be similar to, or highly distinct from, those occurring in vivo, owing to the complex nature of the systems. Novel assemblies may further result due to controlled shape changes in building blocks.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Glassy correlated state induced by disorder in the frustrated antiferromagnet Tb 2 Zr 2 O 7

Here, we study the low-temperature thermomagnetic properties of the polycrystalline material Tb 2 Zr 2 O 7 through ac susceptibility and specific heat measurements. This zirconate displays a defect-fluorite structure in which the magnetic Tb 3+ and nonmagnetic Zr 4+ cations sit randomly on the same metal sublattice. No long-range magnetic order is found down to 100 mK, although dominant antiferromagnetic interactions are observed and the spins remain dynamic down to the lowest temperatures investigated. We observed a frequency-dependent peak around 2.5 K which is well described by many models of a canonical spin-glass transition. In-field specific heat measurements and the recovered entropy of the system R ln(4) suggest a two doublets ground state separated by 7 K. Comparisons to the pyrochlores Tb 2 Ti 2 O 7 and Tb 2 Hf 2 O 7 reinforce the collective spin-glass-type behavior and the opening for discussions of an exotic Coulomb phase in this material.

36 MATERIALS SCIENCE↗
NASA NTRS2015

Experimentally Shocked and Altered Basalt: Laboratory Analogs for Calibration of Mars Remote Sensing and In Situ Data

Calcium phosphate (likely chloroapatite) is formed in the alteration experiments and is more abundant in the altered and shocked sample probably due to increased surface area exposed to alteration fluids resulting from shock damage in the form of both brittle and structural deformation to the starting material (Figs 1 & 3). Apatite forms in basic conditions so the closed system alteration experiment must be buffered by the basalt starting material to create a fluid chemistry environment evolving from neutral at the start to alkaline after 21 days at 160 degrees Centigrade. Plagioclase feldspar in the unshocked sample (Fig. 2) has undergone a solid-state transformation to maskelynite, a disordered phase that is not manifest in the X-ray diffraction pattern of the shocked sample (Fig.4). Olivine and ulvospinel that are present in the starting material can be detected by X-ray diffraction in the shocked and altered sample (Fig. 4). Tungsten from the sample holder used in the shock experiments dominates the X-ray diffraction pattern of the shocked and altered sample (Fig. 4). Samples were weighed after the alteration experiments to determine mass loss and predict the amount of material available for the planned analyses from the shock experiments. Within the constraints of these experiments, mass loss is negligible. The samples will next be characterized by Moessbauer and Vis-Near Infrared spectroscopy, the results of which will be compared to the Mars Exploration Rovers and Mars Reconnaissance Orbiter data sets respectively.

Bell, M. S.↗
DOE OSTI2023

Random magnetic field and the Dirac Fermi surface

In this paper, we study a single two-dimensional Dirac fermion at finite density, subject to a quenched random magnetic field. At low energies and sufficiently weak disorder, the theory maps onto an infinite collection of 1D chiral fermions (associated to each point on the Fermi surface) coupled by a random vector potential. This low-energy theory exhibits an exactly solvable random fixed line, along which we directly compute various disorder-averaged observables without the need for the usual replica, supersymmetry, or Keldysh techniques. We find the longitudinal dc conductivity in the collisionless $\hbar$ω/k B T→∞ limit to be nonuniversal and to vary continuously along the fixed line.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Active learning of ternary alloy structures and energies

Abstract Machine learning models with uncertainty quantification have recently emerged as attractive tools to accelerate the navigation of catalyst design spaces in a data-efficient manner. Here, we combine active learning with a dropout graph convolutional network (dGCN) as a surrogate model to explore the complex materials space of high-entropy alloys (HEAs). We train the dGCN on the formation energies of disordered binary alloy structures in the Pd-Pt-Sn ternary alloy system and improve predictions on ternary structures by performing reduced optimization of the formation free energy, the target property that determines HEA stability, over ensembles of ternary structures constructed based on two coordinate systems: (a) a physics-informed ternary composition space, and (b) data-driven coordinates discovered by the Diffusion Maps manifold learning scheme. Both reduced optimization techniques improve predictions of the formation free energy in the ternary alloy space with a significantly reduced number of DFT calculations compared to a high-fidelity model. The physics-based scheme converges to the target property in a manner akin to a depth-first strategy, whereas the data-driven scheme appears more akin to a breadth-first approach. Both sampling schemes, coupled with our acquisition function, successfully exploit a database of DFT-calculated binary alloy structures and energies, augmented with a relatively small number of ternary alloy calculations, to identify stable ternary HEA compositions and structures. This generalized framework can be extended to incorporate more complex bulk and surface structural motifs, and the results demonstrate that significant dimensionality reduction is possible in thermodynamic sampling problems when suitable active learning schemes are employed.

Chemistry↗
DOE OSTI2020

A Fluorination Method for Improving Cation-Disordered Rocksalt Cathode Performance

In Li-rich cation-disordered rocksalt oxide cathodes (DRX), partial fluorine substitution in the oxygen anion sublattice can increase the capacity contribution from transition-metal (TM) redox while reducing that from the less reversible oxygen redox. To date, limited fluorination substitution has been achieved by introducing LiF precursor during the solid-state synthesis. To take full advantage of the fluorination effect, however, a higher F content is desired. In the present study, the successful use of a fluorinated polymeric precursor is reported to increase the F solubility in DRX and the incorporation of F content up to 10–12.5 at% into the rocksalt lattice of a model Li-Mn-Nb-O (LMNO) system, largely exceeding the 7.5 at% limit achieved with LiF synthesis. Higher F content in the fluorinated-DRX (F-DRX) significantly improves electrochemical performance, with a reversible discharge capacity of ≈255 mAh g –1 achieved at 10 at% of F substitution. After 30 cycles, up to a 40% increase in capacity retention is achieved through the fluorination. Overall, the study demonstrates the feasibility of using a new and effective fluorination process to synthesize advanced DRX cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

The surface of halide perovskites from nano to bulk

The surface of a semiconductor often has a key role in determining its properties. Here, for metal halide perovskites, understanding the surface features and their impact on the materials and devices is becoming increasingly important. At length scales down to the nanoscale regime, surface features become dominant in regulating the properties of perovskite materials, owing to the high surface-to-volume ratio. For perovskite bulk films in the micrometre range, defects and structural disorder readily form at the surface and affect device performance. Through concerted efforts to optimize processing techniques, high-quality perovskite thin films can now be fabricated with monolayer-like polycrystalline grains or even single crystals. Surface defects therefore remain the major obstacle to progress, pushing surface studies to the forefront of perovskite research. In this Review, we summarize and assess recent advances in the understanding of perovskite surfaces and surface strategies towards improving perovskite materials and the efficiency and stability of perovskite devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hydrodynamic electron transport in graphene Hall-bar devices

Here we consider hydrodynamic electron transport in the Hall-bar geometry. The theory is developed for systems with non-Galilean-invariant electron liquids. We show that inhomogeneity of the electron density induced by long-range disorder and gating leads to mixing between the hydrodynamic transport mode and transport relative to the electron liquid. For graphene systems near charge neutrality, these effects lead to strong coupling of the hydrodynamic flow to charge transport. As a result, the effective electrical conductivity of the system may significantly exceed the intrinsic conductivity of the electron liquid. We obtain analytic expressions for the thermoelectric transport coefficients of the system as a function of density in the full crossover region between clean and disorder-dominated regimes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Polyhexatic and polycrystalline states of skyrmion lattices

We report Monte Carlo studies of lattices of up to 10 5 skyrmions treated as particles with negative core energy and repulsive interaction obtained from a microscopic spin model. Temperature dependence of translational and orientational correlations has been investigated for different experimental protocols and initial conditions. Cooling the skyrmion liquid from a fully disordered high-temperature state results in the formation of a skyrmion polycrystal. A perfect skyrmion lattice prepared at T = 0, on raising temperature undergoes a first-order melting transition into a polyhexatic state that consists of large orientationally ordered domains of fluctuating shape. On the further increasing temperature, these domains decrease in size, leading to a fully disordered liquid of skyrmions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Hydration and Restructuring of Polar Polymer Interfaces: Implications in Antifouling and Responsive Materials

Manipulating polymer interfaces is crucial for understanding how structure influences function in applications spanning biofouling prevention to energy storage. Moreover, observing how polymers adapt their microscopic structure to changes in their local environment can reveal essential properties that govern their performance in such applications, providing key insights into how to design more effective interfaces. Here, in this study, a series of “grafting-from” polymer brushes with side chains varying in charge, are probed by sum frequency generation (SFG) and modeled using all-atom molecular dynamics (MD) simulations to elucidate how chemical makeup and charge mediate interfacial restructuring in dry versus hydrated states. Results show that charge, in progressing from nonpolar to cationic to zwitterionic, results in dramatic changes in interfacial structure and overall hydration. While net neutral systems, regardless of bulk phase polarity, show minimal interfacial water structuring, the cationic species exhibits strong bulk water signals from the surface potential. Meanwhile, the polymer brushes themselves restructure in water differently independent of charge, impacting the functional groups that are presented to the aqueous phase. Nonpolar and cationic species for instance undergo a change in alkyl group orientations to accommodate hydrating water molecules, whereas the zwitterionic polymer becomes completely disordered in water. Overall, the structure-based behavior trends presented herein have implications in antifouling applications and responsive material interfaces.

biointerface↗
NASA NTRS2010

Different Perspectives on Asthenia in Astronauts and Cosmonauts: International Research Literature

The Behavioral Health and Performance (BHP) Element is one of the six elements within the NASA Human Research Program (HRP) and is responsible for managing four risks: a) The Risk of Performance Decrements due to inadequate Cooperation, Coordination, Communication and Psychological Adaptation within a Team (Team), b) the Risk of Performance Errors due to Sleep Loss, Circadian De-synchronization, Fatigue and Work Overload (Sleep), c) Risk of Behavioral Conditions (BMed), and d) the Risk of Psychiatric Disorders (BMed). The aim of this report is to address some of the recommendations made by the recent NASA HRP Standing Review Panel for the Behavioral Medicine Risk of Psychiatric Disorders. Such recommendations included: a) the inclusion of important national and international literature in English and non-English language materials; including journals, books, magazines, conference reports and b) an extensive literature review of certain types of psychological states to predict, detect, and assess adverse mental states that may negatively affect the psychological well being of the astronauts, specifically asthenia. This report was a collaborative international work effort focused on the evaluation and determination of the importance of continuing research on asthenia as a possible psychological problem that might affect the optimal psychological functioning among crewmembers during long-duration space flight missions. Russian medical personnel (flight surgeons and psychologist) have observed symptoms of asthenia (weakness, increased fatigue, irritability, and attention and memory disorders) in cosmonauts after four months in space (Myasnikov& Zamaleddinov1996; Grigorieve, 1996 ) and believe that asthenia is one of the greater risks that will affect crews? optimal psychological functioning.

Sandoval, Luis↗
DOE OSTI2020

Unprecedented non-hysteretic superelasticity of [001]-oriented NiCoFeGa single crystals

Superelasticity associated with the martensitic transformation has found a broad range of engineering applications. However, the intrinsic hysteresis and temperature sensitivity of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. In this paper, we report a large superelasticity up to 15.2% strain in [001]-oriented NiCoFeGa single crystals, exhibiting non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. In situ synchrotron X-ray diffraction measurements show that the superelasticity is correlated with a stress-induced continuous variation of lattice parameter accompanied by structural fluctuation. Neutron diffraction and electron microscopy observations reveal an unprecedented microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the superelasticity. The discovery of the large elasticity related to the entangled structure paves the way for exploiting elastic strain engineering and development of related functional materials. NiCoFeGa single crystals exhibit large non-hysteretic superelasticity over broad temperature and composition ranges. It is attributed to the continuous phase transition with applied stress, which is related to the fluctuation of entangled ordered and disordered crystal structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tailoring Mid–Gap States of Chalcogenide Glass by Pressure–Induced Hypervalent Bonding Towards the Design of Electrical Switching Materials

Phase change memory (PCM) and ovonic threshold switching (OTS) materials using chalcogenide glass are essential elements in advanced 3D memory chips. The mid–gap states, induced by the disorder and defects in the glass, are the physical mechanisms of the electrical switching behavior, while the origin of these trap states is still under debate and the medium–range clusters that break the global octet rule, such as over–coordinated atoms, are known to be responsible in various glass. Here, it is discovered that a large fraction of over–coordinated clusters fails to generate mid–gap states, which are probably caused by hypervalent bonding, a multi–centered covalent bond participated by delocalized lone–pair electrons. This is confirmed by the pressure–driven simulations of amorphous GeSe models, in which it is found that octahedral motifs and hypervalent bonds prevent the over–coordinated medium–range clusters from providing excessive electrons. In practical applications, compatible dopants can be used to change the number of hypervalent bonds, thus controlling the number of mid–gap states and consequently the performance of PCM and OTS materials. Finally, these results reveal the origin of mid–gap states in chalcogenide glasses, enabling extensive control in the development of pioneering electrical switching materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Impact of disorder on dynamics and ordering in the honeycomb-lattice iridate Na 2 IrO 3

Kitaev's honeycomb spin-liquid model and its proposed realization in materials such as α-RuCl 3 , Li 2 IrO 3 , and Na 2 IrO 3 continue to present open questions about how the dynamics of a spin liquid are modified in the presence of non-Kitaev interactions as well as the presence of inhomogeneities. Here we use 23 Na nuclear magnetic resonance to probe both static and dynamical magnetic properties in single-crystal Na 2 IrO 3 . We find that the NMR shift follows the bulk susceptibility above 30 K but deviates from it below; moreover below T N the spectra show a broad distribution of internal magnetic fields. Both of these results provide evidence for inequivalent magnetic sites at low temperature, suggesting inhomogeneities are important for the magnetism. The spin-lattice relaxation rate is isotropic and diverges at T N , suggesting that the Kitaev cubic axes may control the critical quantum spin fluctuations. Finally, in the ordered state, we observe gapless excitations, which may arise from site substitution, emergent defects from milder disorder, or possibly be associated with nearby quantum paramagnetic states distinct from the Kitaev spin liquid.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Tailoring the Redox Reactions for High-Capacity Cycling of Cation-Disordered Rocksalt Cathodes

Cation-disordered rocksalts (DRXs) have emerged as a new class of high-capacity Li-ion cathode materials. One unique advantage of the DRX chemistry is the structural flexibility that substantially lessens the elemental constraints in the crystal lattice, such as Li content, choice of transition metal redox center paired with appropriate d 0 metal, and incorporation of F anion, which allows optimization of the key redox reactions. Herein, a series of the DRX oxyfluorides based on the Mn redox have been designed and synthesized. By tailoring the stoichiometry of the DRX compositions, high-capacity cycling by promoting the cationic Mn 2+ /Mn 4+ redox reactions while suppressing those from anionic O is successfully demonstrated. A highly fluorinated DRX compound, Li 1.2 Mn 0.625 Nb 0.175 O 1.325 F 0.675 (M 0.625 F 0.675 ), delivers a capacity of ≈170 mAh g -1 at C/3 for 100 cycles. Furthermore, this work showcases the concept of balancing the cationic and anionic redox reactions in the DRX cathodes for improved electrochemical performance through the rational composition design.

25 ENERGY STORAGE↗
DOE OSTI2023

X-ray Absorption Spectroscopy Illustrates the Participation of Oxygen in the Electrochemical Cycling of Li 4 Mn 2 O 5

A combination of oxygen redox and Mn-based oxides would be the best option for high-energy-density Li-ion batteries crucial for a sustainable society. The disordered rock-salt Li 4 Mn 2 O 5 was recently reported to display a very large capacity of 460 mAh/g with moderate reversibility. Previous studies proposed the involvement of lattice oxygen redox in such intriguing electrochemical performance, whereas no direct evidence was presented. To clarify the charge compensation mechanism, we systematically investigated the evolution of the electronic structure of both Mn and O upon cycling via Mn/OK-edge X-ray absorption spectroscopy (XAS). Mn K-edge XAS unequivocally demonstrates the participation of Mn redox upon the initial stages of charging, yet changes are arrested at the high potentials, while O continues to evolve according to O K-edge XAS. Upon discharging, both Mn and O are simultaneously reduced, but to states different from pristine. In conclusion, the results highlight the significance of a disordered structure in maintaining the reversible redox chemistry of both transition metals and oxygen to design cathode materials with high energy density.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗