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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

A model predicting the evolution of ice particle size spectra and radiative properties of cirrus clouds. Part 2: Dependence of absorption and extinction on ice crystal morphology

This study builds upon the microphysical modeling described in Part 1 by deriving formulations for the extinction and absorption coefficients in terms of the size distribution parameters predicted from the micro-physical model. The optical depth and single scatter albedo of a cirrus cloud can then be determined, which, along with the asymmetry parameter, are the input parameters needed by cloud radiation models. Through the use of anomalous diffraction theory, analytical expressions were developed describing the absorption and extinction coefficients and the single scatter albedo as functions of size distribution parameters, ice crystal shapes (or habits), wavelength, and refractive index. The extinction coefficient was formulated in terms of the projected area of the size distribution, while the absorption coefficient was formulated in terms of both the projected area and mass of the size distribution. These properties were formulated as explicit functions of ice crystal geometry and were not based on an 'effective radius.' Based on simulations of the second cirrus case study described in Part 1, absorption coefficients predicted in the near infrared for hexagonal columns and rosettes were up to 47% and 71% lower, respectively, than absorption coefficients predicted by using equivalent area spheres. This resulted in single scatter albedos in the near-infrared that were considerably greater than those predicted by the equivalent area sphere method. Reflectances in this region should therefore be underestimated using the equivalent area sphere approach. Cloud optical depth was found to depend on ice crystal habit. When the simulated cirrus cloud contained only bullet rosettes, the optical depth was 142% greater than when the cloud contained only hexagonal columns. This increase produced a doubling in cloud albedo. In the near-infrared (IR), the single scatter albedo also exhibited a significant dependence on ice crystal habit. More research is needed on the geometrical properties of ice crystals before the influence of ice crystal shape on cirrus radiative properties can be adequately understood. This study provides a way of coupling the radiative properties of absorption, extinction, and single scatter albedo to the microphysical properties of cirrus clouds. The dependence of extinction and absorption on ice crystal shape was not just due to geometrical differences between crystal types, but was also due to the effect these differences had on the evolution of ice particle size spectra. The ice particle growth model in Part 1 and the radiative properties treated here are based on analytical formulations, and thus represent a computationally efficient means of modeling the microphysical and radiative properties of cirrus clouds.

Mitchell, David L.↗
DOE OSTI2023

Adaptively driven X-ray diffraction guided by machine learning for autonomous phase identification

Machine learning (ML) has become a valuable tool to assist and improve materials characterization, enabling automated interpretation of experimental results with techniques such as X-ray diffraction (XRD) and electron microscopy. Because ML models are fast once trained, there is a key opportunity to bring interpretation in-line with experiments and make on-the-fly decisions to achieve optimal measurement effectiveness, which creates broad opportunities for rapid learning and information extraction from experiments. Here, we demonstrate such a capability with the development of autonomous and adaptive XRD. By coupling an ML algorithm with a physical diffractometer, this method integrates diffraction and analysis such that early experimental information is leveraged to steer measurements toward features that improve the confidence of a model trained to identify crystalline phases. We validate the effectiveness of an adaptive approach by showing that ML-driven XRD can accurately detect trace amounts of materials in multi-phase mixtures with short measurement times. The improved speed of phase detection also enables in situ identification of short-lived intermediate phases formed during solid-state reactions using a standard in-house diffractometer. Our findings showcase the advantages of in-line ML for materials characterization and point to the possibility of more general approaches for adaptive experimentation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Quantitative Analysis of the Morphology of {101} and {001} Faceted Anatase TiO 2 Nanocrystals and Its Implication on Photocatalytic Activity

The atomistic structure and morphology (shape and size) of nanomaterials have strong influences on their physical and chemical properties. However, many characterization techniques focus exclusively on one length-scale regime or another when developing quantitative morphology/structural models. In this article, we demonstrate that powder X-ray diffraction and neutron pair distribution function (PDF) can be used to obtain accurate average morphology and atomistic structure of {001} and {101} faceted anatase TiO 2 nanocrystals based on differential evolution refinements using Debye scattering equation calculations. It is also demonstrated that the morphology polydispersity of TiO 2 nanocrystals can be effectively obtained from the diffraction data via a numerical refinement routine. The morphology refinement results are in good agreement with those from transmission electron microscopy and the modeling of small angle neutron scattering data. This method is successfully used to quantify the facet-specified photocatalytic hydrogen evolution activity of anatase TiO 2 nanocrystals with different {001} to {101} ratios. It is found that the sample with an intermediate amount of both {001} and {101} facets shows the best photocatalytic hydrogen evolution reaction (HER) activity. It is expected that the simultaneous structure and morphology refinement technique can be generally used to study the relationship between morphology and functionality of nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Analysis of an anti-reflecting nanowire transparent electrode for solar cells

Transparent electrodes are an important component in many optoelectronic devices, especially solar cells. In this study, we investigate a nanowire transparent electrode that also functions as an anti-reflection coating for silicon solar cells, taking into account the practical constraints that the electrode is typically encapsulated and needs to be in electric contact with the semiconductor. Numerical simulations show that the electrode can provide near-perfect broadband anti-reflection over much of the frequency range above the silicon band gap for both polarizations while keeping the sheet resistance sufficiently low. To provide insights into the physics mechanism of this broadband anti-reflection, we introduce a generalized Fabry–Perot model, which captures the effects of the higher order diffraction channels as well as the modification of the reflection coefficient of the interface introduced by the nanowires. This model is validated using frequency-domain electromagnetic simulations. Finally, our work here provides design guidelines for nanowire transparent electrode in a device configuration that is relevant for solar cell applications.

14 SOLAR ENERGY↗
DOE OSTI2016

Relating the structure of geminal amido esters to their molecular hyperpolarizability

Advanced organic non-linear optical (NLO) materials have attracted increasing attention due to their multitude of applications in modern telecommunication devices. Arguably the most important advantage of organic NLO materials, relative to traditionally used inorganic NLO materials, is their short optical response time. Geminal amido esters with their donor-x-acceptor (D-π-A) architecture exhibit high levels of electron delocalization and substantial intramolecular charge transfer, which should endow these materials with short optical response times and large molecular (hyper)polarizabilities. In order to test this hypothesis, the linear and second-order non-linear optical properties of five geminal amido esters, ( E )-ethyl 3-(X-phenylamino)-2-(Y-phenylcarbamoyl)acrylate (1: X = 4-H,Y = 4-H; 2: X= 4-CH 3 , Y = 4-CH 3 ; 3: X = 4-NO 2 , Y = 2,5-OCH 3 ; 4: X = 2-Cl, Y = 2-Cl; 5: X = 4-Cl, Y = 4-Cl) were synthesized and characterized, whereby NLO structure-function relationships were established including intramolecular charge transfer characteristics, crystal field effects, and molecular first hyperpolarizabilities β. Given the typically large errors (10-30%) associated with the determination of (β) coefficients, three independent methods were used: i) density functional theory, ii) hyper-Rayleigh scattering, and iii) high-resolution X-ray diffraction data analysis based on multipolar modeling of electron densities at each atom. These three methods delivered consistent values of β, and based on these results, 3 should hold the most promise for NLO applications. In conclusion, the correlation between the molecular structure of these geminal amido esters and their linear and non-linear optical properties thus provide molecular design guidelines for organic NLO materials; this leads to the ultimate goal of generating bespoke organic molecules to suit a given NLO device application.

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

Geo-Responsive Chemomechanics in Aluminum Oxyhydroxide via Alkali-Driven Dehydroxylation for Supercritical Geothermal Systems

Widespread use of enhanced geothermal systems can revolutionize global renewable electrical power access, yet its advancement is hindered by the inherent instability of Portland cement-based chemistries for geothermal well construction under high-temperature corrosive conditions. Here, in this work, we demonstrate the tunable mechanical performance of aluminum oxyhydroxides as cementitious materials through an alkali-controlled dehydroxylation reaction pathway for long-term applications under supercritical geothermal environments. Notably, the synthesized aluminum oxyhydroxides demonstrate remarkable stability, maintaining superior mechanical performance under supercritical conditions for over 30 days. Synchrotron X-ray diffraction, spectroscopy measurements and geochemical thermodynamic modeling uncover that the gibbsite dehydroxylation pathway functions as a key dial for tuning the chemomechanics, rendering the aluminum oxyhydroxide a strong cementitious material. By uncovering the mechanistic role of alkali-driven dehydroxylation, this work proposes a cementitious chemistry distinct from conventional Portland cement and geopolymer-dominated alkali-activated systems, laying the groundwork for developing next-generation cementitious materials for supercritical geothermal energy exploitation.

15 GEOTHERMAL ENERGY↗
DOE OSTI2019

Multi-level chirality in liquid crystals formed by achiral molecules

Complex materials often exhibit a hierarchical structure with an intriguing mechanism responsible for the 'propagation' of order from the molecular to the nano- or micro-scale level. In particular, the chirality of biological molecules such as nucleic acids and amino acids is responsible for the helical structure of DNA and proteins, which in turn leads to the lack of mirror symmetry of macro-bio-objects. To fully understand mechanisms of cross-level order transfer there is an intensive search for simpler artificial structures exhibiting hierarchical arrangement. Here we present complex systems built of achiral molecules that show four levels of structural chirality: layer chirality, helicity of a basic repeating unit, mesoscopic helix and helical filaments. The structures are identified by a combination of hard and soft x-ray diffraction measurements, optical studies and theoretical modelling. Similarly to many biological systems, the studied materials exhibit a coupling between chirality at different levels.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Harnessing metastability for grain size control in multiprincipal element alloys during additive manufacturing

Abstract Controlling microstructure in fusion-based metal additive manufacturing (AM) remains a significant challenge due to the many parameters that directly impact solidification condition. Multiprincipal element alloys (MPEAs), also known as high entropy alloys, offer a vast compositional space to design for microstructural engineering due to their chemical complexity and exceptional properties. Here, we use the FeMnCoCr system as a model platform for exploring alloy design in MPEAs for AM. By exploiting the decreasing stability of the face-centered cubic phase with increasing Mn content, we achieve notable grain refinement and breakdown of epitaxial columnar grain growth. We employ a multifaceted approach encompassing thermodynamic modeling, operando synchrotron X-ray diffraction, multiscale microstructural characterization, and mechanical testing to gain insight into the solidification physics and its ramifications on the resulting microstructure of FeMnCoCr MPEAs. This work aims toward tailoring desirable grain sizes and morphology through targeted manipulation of phase stability, thereby advancing microstructure control in AM applications.

Wakai, Akane↗
DOE OSTI2019

Anisotropic structural dynamics of monolayer crystals revealed by femtosecond surface X-ray scattering

Ultrafast X-ray scattering is one of the primary tools to track intrinsic crystallographic evolution with atomic accuracy in real time. However, its application to study nonequilibrium structural properties at the two-dimensional limit remains a long-standing challenge due to a significant reduction of diffraction volume and complexity of data analysis. Here, we report femtosecond surface X-ray diffraction in combination with crystallographic model-refinement calculations to quantify the ultrafast structural dynamics of monolayer WSe 2 crystals supported on a substrate. We found the absorbed optical photon energy is preferably coupled to the in-plane lattice vibrations within one picosecond whereas the out-of-plane lattice vibration amplitude remains unchanged during the first ten picoseconds. The model-assisted fitting suggests an asymmetric intralayer spacing change upon excitation. The observed nonequilibrium anisotropic structural dynamics agrees with first-principles modelling in both real and momentum space, marking the distinct structural dynamics of monolayer crystals from their bulk counterparts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Electrochemical (de)lithiation of silver ferrite and composites: mechanistic insights from ex situ, in situ, and operando X-ray techniques

Here, the structure of pristine AgFeO 2 and phase makeup of Ag 0.2 FeO1.6 (a one-pot composite comprised of nanocrystalline stoichiometric AgFeO 2 and amorphous γ-Fe 2 O 3 phases) was investigated using synchrotron x-ray diffraction. A new stacking-fault model was proposed for AgFeO2 powder synthesized using the co-precipitation method. The lithiation/de-lithiation mechanisms of silver ferrite, AgFeO 2 and Ag 0.2 FeO 1.6 were investigated using ex-situ, in-situ, and operando characterization techniques. An amorphous γ-Fe 2 O 3 component in the Ag 0.2 FeO 1.6 sample is quantified. Operando XRD of electrochemically reduced AgFeO 2 and Ag 0.2 FeO 1.6 composites demonstrated differences in the structural evolution of the nanocrystalline AgFeO 2 component. As complimentary techniques to XRD, ex-situ x-ray Absorption Spectroscopy (XAS) provided insight into the short-range structure of the (de)lithiated nanocrystalline electrodes, and a novel in-situ high energy x-ray fluorescence nanoprobe (HXN) mapping measurement was applied to spatially resolve the progression of discharge. Based on the results, a redox mechanism is proposed where the full reduction of Ag + to Ag0 and partial reduction of Fe 3+ to Fe 2+ occur on reduction to 1.0 V, resulting in a Li 1+y Fe III Fe II yO 2 phase. The Li 1+y Fe III Fe II yO 2 phase can then reversibly cycle between Fe 3+ and Fe 2+ oxidation states, permitting good capacity retention over 50 cycles. In the Ag 0.2 FeO 1.6 composite, a substantial amorphous γ-Fe 2 O 3 component is observed which discharges to rock salt LiFe 2 O 3 and Fe 0 metal phase in the 3.5 – 1.0 V voltage range (in parallel with the AgFeO 2 mechanism), and reversibly reoxidizes to a nanocrystalline iron oxide phase.

25 ENERGY STORAGE↗
DOE OSTI2023

Elucidating a dissolution–deposition reaction mechanism by multimodal synchrotron X-ray characterization in aqueous Zn/MnO 2 batteries

Aqueous Zn/MnO 2 batteries with their environmental sustainability and competitive cost, are becoming a promising, safe alternative for grid-scale electrochemical energy storage. Here, presented as a promising design principle to deliver a higher theoretical capacity, this work offers fundamental understanding of the dissolution–deposition mechanism of Zn/β-MnO 2 . A multimodal synchrotron characterization approach including three operando X-ray techniques (powder diffraction, absorption spectroscopy, and fluorescence microscopy) is coupled with elementally resolved synchrotron X-ray nano-tomography. Together they provide a direct correlation between structural evolution, reaction chemistry, and 3D morphological changes. Operando synchrotron X-ray diffraction and spectroscopy show a crystalline-to-amorphous phase transition. Quantitative modeling of the operando data by Rietveld refinement for X-ray diffraction and multivariate curve resolution (MCR) for X-ray absorption spectroscopy are used in a complementary fashion to track the structural and chemical transitions of both the long-range (crystalline phases) and short-range (including amorphous phases) ordering upon cycling. Scanning X-ray microscopy and full-field nano-tomography visualizes the morphology of electrodes at different electrochemical states with elemental sensitivity to spatially resolve the formation of the Zn- and Mn-containing phases. Overall, this work critically indicates that for Zn/MnO 2 aqueous batteries, the reaction pathways involving Zn–Mn complex formation upon cycling become independent of the polymorphs of the initial electrode and sheds light on the interplay among structural, chemical, and morphological evolution for electrochemically driven phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Mixing of two collinear Rayleigh waves in an isotropic nonlinear elastic half-space

Nonlinear mixing of two collinear, initially monochromatic, Rayleigh waves propagating in the same direction in an isotropic, nonlinear elastic solid is investigated analytically. A system of coupled ordinary differential equations is derived based on the Lagrange equations of the second kind to predict the evolution of the higher harmonic and combination frequency components of the fundamentals waves. Numerical results show that the energy transfer is larger for higher frequencies, and that the oscillation of the energy between the different frequency components depends on the amplitudes and frequencies of the fundamental waves. Furthermore, it is illustrated that the horizontal velocity component can form a shock wave while the vertical velocity component can form a pulse. The occurrence of these effects is independent of the specific fundamental frequencies and amplitudes that are mixed. However, the nonlinear interaction is more efficient when the mixing frequencies are close to each other which increases both effects. The analytical model is then extended by implementing diffraction effects in the parabolic approximation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

In-situ probing of coupled atomic restructuring and metallicity of oxide heterointerfaces induced by polar adsorbates

Microscopic understanding of the surface-controlled conductivity of the two dimensional electron gas at complex oxide interfaces is crucial for developing functional interfaces. We observe conductivity and structural modification using in-situ synchrotron surface x-ray diffraction as the surface of a model LaAlO 3 /SrTiO 3 (001) heterostructure is changed by polar adsorbates. We find that polar adsorbate-induced interfacial metallicity reduces polar distortions in the LaAlO 3 layer. First-principles density functional theory calculations show that surface dipoles introduced by polar adsorbates lead to additional charge transfer and the reduction of polar displacements in the LaAlO 3 layer, consistent with the experimental observations. Our study supports that internal structural deformations controlling functionalities can be driven without the application of direct electrical or thermal bias and offers a route to tuning interfacial properties. Furthermore, these results also highlight the important role of in-situ x-ray scattering with atomic resolution in capturing and exploring structural distortions and charge density changes caused by external perturbations such as chemical adsorption, redox reaction, and generation and/or annihilation of surface defects.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Two-dimensional quantum universality in the spin-1/2 triangular-lattice quantum antiferromagnet Na 2 BaCo(PO 4 ) 2

An interplay of geometrical frustration and strong quantum fluctuations in a spin-1/2 triangular-lattice antiferromagnet (TAF) can lead to exotic quantum states. Here, we report the neutron-scattering, magnetization, specific heat, and magnetocaloric studies of the recently discovered spin-1/2 TAF Na 2 BaCo(PO 4 ) 2 , which can be described by a spin-1/2 easy axis XXZ model. The zero-field neutron diffraction experiment reveals an incommensurate antiferromagnetic ground state with a significantly reduced ordered moment of about 0.54(2) μ B /Co. Different magnetic phase diagrams with magnetic fields in the a b plane and along the easy c -axis were extracted based on the magnetic susceptibility, specific heat, and elastic neutron-scattering results. In addition, two-dimensional (2D) spin dispersion in the triangular plane was observed in the high-field polarized state, and microscopic exchange parameters of the spin Hamiltonian have been determined through the linear spin wave theory. Consistently, quantum critical behaviors with the universality class of d = 2 and ν z = 1 were established in the vicinity of the saturation field, where a Bose–Einstein condensation (BEC) of diluted magnons occurs. The newly discovered quantum criticality and fractional magnetization phase in this ideal spin-1/2 TAF present exciting opportunities for exploring exotic quantum phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Thermally induced transformations of Au@Cu 2 O core–shell nanoparticles into Au–Cu nanoparticles from temperature-programmed in situ powder X-ray diffraction

Temperature-programmed in situ X-ray diffraction with whole-powder-pattern modeling is used to investigate the reaction of Au@Cu 2 O core–shell nanoparticles to form nanocrystalline bimetallic Cu x Au 1− x alloys ( x = 0, 0.25, 0.5, 0.75, 1.0) in a reducing atmosphere. The mechanisms of the reactions are key to informed design of tailored non-equilibrium nanostructures for catalytic and plasmonic materials. The Au@Cu 2 O reaction is initiated by reduction of the Cu 2 O cuprite shell to form nanocrystalline metallic Cu at about 413 K. Alloying begins immediately upon formation of metallic Cu at 413 K, with the nucleation of an Au-rich alloy phase which reaches the nominal Cu content of the overall system stoichiometry by 493 K. All bimetallic alloys form a transient ordered Cu 3 Au intermetallic compound at intermediate temperatures, with the onset of ordering and subsequent disordering varying by composition. No evidence for an ordered Au 3 Cu intermetallic is found for any composition. Significant crystal growth in the bimetallic phase is apparent at higher temperatures, with the onset temperature increasing with Cu concentration and initial Cu-shell thickness. The reduction of the cuprite phase is slowed by the presence of the core–shell interface, and crystal growth in the Cu shell is completely suppressed within the alloy systems.

Chemistry↗
DOE OSTI2017

Analysis of a Wave-Powered, Reverse-Osmosis System and Its Economic Availability in the United States: Preprint

A wave energy converter (WEC) system has the potential to convert the wave energy resource directly into the high-pressure flow that is needed by the desalination system to permeate saltwater through the reverse-osmosis membrane to generate clean water. In this study, a wave-to-water numerical model was developed to investigate the potential use of a wave-powered desalination system (WPDS) for water production in the United States. The model was developed by coupling a time-domain radiation-and-diffraction-method-based numerical tool (WEC-Sim) for predicting the hydrodynamic performance of WECs with a solution-diffusion model that was used to simulate the reverse-osmosis process. To evaluate the feasibility of the WPDS, the wave-to-water numerical model was applied to simulate a desalination system that used an oscillating surge WEC device to pump seawater through the system. The annual water production was estimated based on the wave resource at a reference site on the coast of northern California to investigate the potential cost of water in that area, where the cost of water and electricity is high compared to other regions. In the scenario evaluated, for a 100-unit utility-scale electricity-producing array, the estimated levelized cost of energy for these WECs is about 3-6 times the U.S.'s current, unsubsidized electricity rates. However, with clean water as an end product and by directly producing pressurized water with WECs, rather than electricity as an intermediary, it is presently only 12 percent greater than typical water cost in California. This study suggests that a WEC array that produces water may be a viable, near-term solution to the nation's water supply, and the niche application of the WPDS may also provide developers with new opportunities to further develop technologies that benefit both the electric and drinking water markets.

16 TIDAL AND WAVE POWER↗