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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
NASA NTRS1974

Virial expansion of the second layer in physical adsorption - An ab initio calculation for helium on argon crystal

A model of helium adsorption on an argon crystal is built up from the premise that local adsorption predominates in the first layer and nonlocal adsorption in the second. Application of the virial expansion theorem to the second layer gives a series in which the first term represents the motion of a single molecule in the external potential field and the second a two-body interaction under this field. The thermodynamic functions of the adsorbed phase are calculated ab initio, the gas-solid interaction potential being derived from lattice summation and the partition function from an appropriate choice of a site-spacing polynomial to describe the periodic potential. The mutual interaction of adsorbed molecules is calculated with a two-dimensional Lennard-Jones potential. The second virial coefficient is calculated and its dependence on temperature and choice of potential is studied. It is found that the second virial coefficient is very well approximated by a two-dimensional gas in free space. The adsorption isotherm, isosteric heat, and specific heat are obtained and compared with the results of Ross and Steele, giving excellent agreement.

Oh, B. K.↗
NASA NTRS2004

Petrology of New Stannern-trend Eucrites and Eucrite Genesis

Eucrites are basaltic meteorites of the howardite-eucrite-diogenite (HED) suite that originated on a differentiated asteroid, possibly 4 Vesta. Basaltic eucrites are divided into three subgroups based on composition: main group, Stannern-trend, and Nuevo Laredo-trend. The main group and Nuevo Laredo-trend define a sequence formed by fractional crystallization of pigeonite and plagioclase from primitive parent melts [2, 3]. The Stannern-trend cannot be explained this way, but may rather represent a partial-melt sequence of their parent body. However, this model seems inadequate to explain eucrite siderophile element contents, and it is difficult to develop a single unifying model for petrogenesis of all eucrites. Until recently, there were only four Stannern- trend eucrites. One is an anomalous partial cumulate. There is little geochemical variation among these meteorites, so the Stannern-trend was poorly defined. Geochemical studies have identified four additional eucrites as members of the Stannern-trend; one extends the Stannern-trend closer to the main group [5]. No detailed descriptions of these rocks have been published. In order to better integrate these eucrites into the suite, we have done petrologic study of them. They are: LEW 88010, PCA 82501, PCA 91006 and PCA 91179.

Gardner, K. G.↗
NASA NTRS2016

Basaltic Shergottite NWA 856: Differentiation of a Martian Magma

NWA 856 or Djel Ibone, is a basaltic shergottite discovered as a single stone of 320 g in South Morocco in April, 2001. This meteorite is fresh, i.e. shows minimal terrestrial weathering for a desert find. No shergottite discovered in North Africa can be paired with NWA 856. The purpose of this study is to constrain its crystallization history using textural observations, crystallization sequence modeling and in-situ trace element analysis in order to understand differentiation in shergottite magmatic systems.

Ferdous, J.↗
DOE OSTI2022

Q-POP-Thermo: A general-purpose thermodynamics solver for ferroelectric materials

We report that Q-POP-Thermo is a program designed to compute thermodynamic monodomain equilibrium states and their properties for ferroelectric single crystals and thin films based on the Landau-Ginzburg-Devonshire (LGD) Theory. Utilizing symbolic manipulation with the SymPy Library, the governing equations along with appropriate boundary conditions are solved for speedy minimization of the free energy of a crystal. Utilizing the popular Differential Evolution algorithm, with appropriate hybridization, multiple phase diagrams, such as the pressure-temperature phase diagram for bulk single crystals and the common strain-temperature phase diagram for monodomain thin-film systems can be readily generated. Furthermore, a variety of material properties of stable ferroelectric phases, including dielectric, piezoelectric, and electrocaloric properties, can simultaneously be calculated. Validation studies are presented for both thin-film and single crystal systems to test the effectiveness and capability of the open-source program.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Electronic structure theory on modeling short-range noncovalent interactions between amino acids

While short-range noncovalent interactions (NCIs) are proving to be of importance in many chemical and biological systems, these atypical bindings happen within the so-called van der Waals envelope and pose an enormous challenge for current computational methods. We introduce SNCIAA, a database of 723 benchmark interaction energies of short-range noncovalent interactions between neutral/charged amino acids originated from protein x-ray crystal structures at the “gold standard” coupled-cluster with singles, doubles, and perturbative triples/complete basis set [CCSD(T)/CBS] level of theory with a mean absolute binding uncertainty less than 0.1 kcal/mol. Subsequently, a systematic assessment of commonly used computational methods, such as the second-order Møller−Plesset theory (MP2), density functional theory (DFT), symmetry-adapted perturbation theory (SAPT), composite electronic-structure methods, semiempirical approaches, and the physical-based potentials with machine learning (IPML) on SNCIAA is carried out. It is shown that the inclusion of dispersion corrections is essential even though these dimers are dominated by electrostatics, such as hydrogen bondings and salt bridges. Overall, MP2, ωB97M-V, and B3LYP+D4 turned out to be the most reliable methods for the description of short-range NCIs even in strongly attractive/repulsive complexes. SAPT is also recommended in describing short-range NCIs only if the δMP2 correction has been included. The good performance of IPML for dimers at close-equilibrium and long-range conditions is not transferable to the short-range. We expect that SNCIAA will assist the development/improvement/validation of computational methods, such as DFT, force-fields, and ML models, in describing NCIs across entire potential energy surfaces (short-, intermediate-, and long-range NCIs) on the same footing.

Chemistry↗
DOE OSTI2025

Spin dynamics in natural multiferroic pyroxene NaFeSi 2 ⁢O 6

Spin dynamics in the natural mineral aegirine, NaFeSi 2⁢ O 6 , a member of the pyroxene family, was studied by elastic and inelastic neutron scattering. Magnetization and specific-heat measurements as well as single-crystal neutron diffraction maps, taken in the temperature range 2–20 K, confirm two successive magnetic transitions at 8.8 and 5.8 K, consistent with previous studies. The observed spin-wave excitations emerge from the incommensurate magnetic Bragg peaks corresponding to the propagation vector 𝑘 ICM = (0,0.77,0), and extend up to energies of about 1.5 meV. In the low-temperature helical phase, the spin dynamics of the Fe3+ ions is well described by a simple linear spin-wave model. The observed excitations can be modeled using a spin Hamiltonian that includes three primary exchange interactions—intrachain coupling 𝐽 = 0.142⁢(2) ⁢meV, and interchain couplings 𝐽 1 = 0.083⁢(1) ⁢meV and 𝐽 2 = 0.186⁢(1) meV—and an easy-plane anisotropy 𝐷 = 0.020⁢(6)⁢ meV. Furthermore, our results show that no single exchange interaction dominates the spin dynamics. The similar strengths of the intrachain and interchain couplings point to the fact that the magnetic interactions in aegirine are three dimensional rather than confined along one direction. As a result, the system cannot be considered quasi one dimensional, as previously suggested, and calls for further investigations.

Magnetic coupling↗
DOE OSTI2021

Understanding the plasticity contributions during laser-shock loading and spall failure of Cu microstructures at the atomic scales

A hybrid atomic-scale and continuum modeling framework is used to study the microstructural evolution during the laser-induced shock deformation and failure (spallation) of copper microstructures. A continuum two-temperature model (TTM) is used to account for the interaction of Cu atoms with a laser in molecular dynamics (MD) simulations. The MD-TTM simulations study the effect of laser loading conditions (laser fluence) on the microstructure (defects) evolution during various stages of shock wave propagation, reflection, and interaction in single-crystal (sc) Cu systems. In addition, the role of the microstructure is investigated by comparing the defect evolution and spall response of sc-Cu and nanocrystalline (nc) Cu systems. The defect (stacking faults and twin faults) evolution behavior in the metal at various times is further characterized using virtual in situ selected area electron diffraction and x-ray diffraction during various stages of evolution of microstructure. Here, the simulations elucidate the uncertain relation between spall strength and strain-rate and the much stronger relation between the spall strength and the temperatures generated due to laser shock loading for the small Cu sample dimensions considered here.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tiny Sc Allows the Chains to Rattle: Impact of Lu and Y Doping on the Charge-Density Wave in ScV 6 Sn 6

The kagome metals display an intriguing variety of electronic and magnetic phases arising from the connectivity of atoms on a kagome lattice. A growing number of these materials with vanadium–kagome nets host charge–density waves (CDWs) at low temperatures, including ScV 6 Sn 6 , CsV 3 Sb 5 , and V 3 Sb 2 . Curiously, only the Sc version of the RV 6 Sn 6 materials with a HfFe 6 Ge 6 -type structure hosts a CDW (R = Gd–Lu, Y, Sc). In this study, we investigate the role of rare earth size in CDW formation in the RV 6 Sn 6 compounds. Magnetization measurements on our single crystals of (Sc,Lu)V 6 Sn 6 and (Sc,Y)V 6 Sn 6 establish that the CDW is suppressed by substituting Sc by larger Lu or Y. Single-crystal X-ray diffraction reveals that compressible Sn–Sn bonds accommodate the larger rare earth atoms within loosely packed R–Sn–Sn chains without significantly expanding the lattice. We propose that Sc provides extra room in these chains crucial to CDW formation in ScV 6 Sn 6 . Our rattling chain model explains why both physical pressure and substitution by larger rare earth atoms hinder CDW formation despite opposite impacts on lattice size. Here, we emphasize the cooperative effect of pressure and rare earth size by demonstrating that pressure further suppresses the CDW in a Lu-doped ScV 6 Sn 6 crystal. Our model not only addresses why a CDW only forms in the RV 6 Sn 6 materials with tiny Sc but also advances our understanding of why unusual CDWs form in the kagome metals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Quantum simulation of an extended Dicke model with a magnetic solid

Abstract The Dicke model describes the cooperative interaction of an ensemble of two-level atoms with a single-mode photonic field and exhibits a quantum phase transition as a function of light–matter coupling strength. Extending this model by incorporating short-range atom–atom interactions makes the problem intractable but is expected to produce new physical phenomena and phases. Here, we simulate such an extended Dicke model using a crystal of ErFeO 3 , where the role of atoms (photons) is played by Er 3+ spins (Fe 3+ magnons). Through terahertz spectroscopy and magnetocaloric effect measurements as a function of temperature and magnetic field, we demonstrated the existence of a novel atomically ordered phase in addition to the superradiant and normal phases that are expected from the standard Dicke model. Further, we elucidated the nature of the phase boundaries in the temperature–magnetic-field phase diagram, identifying both first-order and second-order phase transitions. These results lay the foundation for studying multiatomic quantum optics models using well-characterized many-body solid-state systems.

Marquez Peraca, Nicolas↗
DOE OSTI2020

Se diffusion in CdTe thin films for photovoltaics

Manipulating CdSeTe bandgrading to enhance photocurrent and carrier lifetime is an essential part of high-performance CdTe photovoltaics (PVs). Here, we examine Se diffusion kinetics in single-crystal and polycrystalline CdTe during deposition, thermal annealing, and CdCl 2 treatments. Se distributions are determined by dynamic secondary-ion-mass spectroscopy and Auger electron spectroscopy depth profiling and coupled with electron backscatter diffraction images of the crystalline structure. Effective bulk and grain boundary diffusion coefficients are determined by analytical models and discussed in the context of processing and film morphology. Se is found to diffuse in CdTe at much higher rates during CdCl 2 treatments than with thermal processing alone. GB diffusion also occurs at a significantly faster rate than bulk diffusion. As a result of these two effects, the near interface bulk and GB Se diffusion during CdCl 2 treatments dominates the bandgrading profiles in CdTe PVs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

Environmental Degradation of Materials: Surface Chemistry Related to Stress Corrosion Cracking

Parallel experiments have been performed in order to develop a comprehensive model for stress cracking (SCC) in structural materials. The central objective is to determine the relationship between the activity and selectivity of the microstructure of structural materials to their dissolution kinetics and experimentally measured SCC kinetics. Zinc was chosen as a prototype metal system. The SCC behavior of two oriented single-crystal disks of zinc in a chromic oxide/sodium sulfate solution (Palmerton solution) were determined. It was found that: (1) the dissolution rate is strongly (hkil)-dependent and proportional to the exposure time in the aggressive environment; and (2) a specific slip system is selectively active to dissolution under applied stress and this slip line controls crack initiation and propagation. As a precursor to potential microgrvity experiments, electrophoretic mobility measurements of zinc particles were obtained in solutions of sodium sulfate (0.0033 M) with concentrations of dissolved oxygen from 2 to 8 ppm. The equilibrium distribution of exposed oriented planes as well as their correlation will determine the particle mobility.

Schwarz, J. A.↗
DOE OSTI2022

Inferring relative dose-dependent color center populations in proton irradiated thoria single crystals using optical spectroscopy

In this work, we have utilized photoluminescence spectroscopy and optical ellipsometry to characterize the dose-dependence of the photoluminescence emission intensity and changes in optical absorption of thoria single crystals subject to irradiation with energetic protons at room- and elevated-temperatures. The photoluminescence peaks and the optical absorption bands are attributed to creation of new electronic states emerging from defects resulting from displacement damage. These bands are most likely associated with electrons trapped at the oxygen vacancy sites similar to color centers formed in other irradiated oxides and halides. Our experimental observations are supported by a standard density functional theory calculation of the electronic structure in pristine and oxygen vacancy-bearing thoria crystals. The dose-dependence of the intensity of the photoluminescence peaks is used to parameterize a rate theory model that estimates the concentration of color centers in the irradiated crystals. This parameterization provides optimized migration barrier parameters for oxygen interstitials and vacancies that simultaneously capture the optical response of the crystals irradiated at room- and elevated-temperature. These optical spectroscopy techniques offer a promising pathway to characterize the population of color centers formed at the sites of oxygen anion vacancies, particularly in irradiated nuclear fuels, where atomic-level defects cannot be readily imaged using electron microscopy. When combined with other direct and indirect characterization tools, our approach can provide new insight into defect formation and accumulation in energy materials over single atomic to extended length scales.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Comment on “STM study of the (111) and (100) surfaces of PdAg, Surf. Sci. 417 (1998) 292–300" and references therein

Investigation of isolated, single atoms on the surfaces of alloys is of great interest in the field of heterogeneous catalysis. Prior studies by Nieuwenhuys, etal. [Surf. Sci. 417 (1998) 292–300 and references therein] showed that annealing the (111) surface of a PdAg bulk alloy yielded a surface with ~5% Pd, predominantly in the form of single atoms, rendering it an ideal model for investigating the reactivity of single Pd atoms. Herein, new evidence is reported that establishes the bulk composition of the PdAg(111) alloy studied previously is 67 % Ag and 33 % Pd, whereas it was reported to be 33 % Ag and 67 % Pd in the prior studies. Furthermore, the bulk composition of a crystal derived from the same PdAg alloy boule used previously was determined using energy-dispersive X-ray spectroscopy (EDS)—a bulk sensitive technique. Surface-sensitive measurements, including X-ray photoelectron spectroscopy, were also performed and are in good agreement with the prior studies by Nieuwenhuys, etal.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Transuranium Sulfide via the Boron Chalcogen Mixture Method and Reversible Water Uptake in the NaCu T S 3 Family

The behavior of 5f electrons in soft ligand environments makes actinides, and especially transuranium chalcogenides, an intriguing class of materials for fundamental studies. Due to the affinity of actinides for oxygen, however, it is a challenge to synthesize actinide chalcogenides using non-metallic reagents. Using the Boron Chalcogen Mixture (BCM) method, we achieved the synthesis of the transuranium sulfide NaCuNpS 3 starting from the oxide reagent, NpO 2 . Via the same synthetic route, the isostructural composition of NaCuUS 3 was synthesized and the material contrasted with NaCuNpS 3 . Single crystals of the U-analog, NaCuUS 3 , were found to undergo an unexpected reversible hydration process to form NaCuUS 3 ·xH 2 O (x ≈ 1.5). Here, a large combination of techniques was used to fully characterize the structure, hydration process, and electronic structures, specifically a combination of single crystal, powder, high temperature powder X-ray diffraction, extended X-ray ab-sorption fine structure, infrared, and inductively coupled plasma spectroscopies, thermogravimetric analysis, and density functional theory calculations. The outcome of these analyses enabled us to determine the composition of NaCuUS 3 ·xH 2 O and obtain a structural model that demonstrated the retention of the local structure within the [CuUS 3 ] – layers throughout the hydration-dehydration process. Band structure, density of states, and Bader charge calculations for NaCuUS 3 , NaCu-US 3 ·xH 2 O, and NaCuNpS 3 along with X-ray absorption near edge structure, UV-vis-NIR and work function measurements on ACuUS 3 (A = Na, K, and Rb) and NaCuUS 3 ·xH 2 O samples were carried out to demonstrate that electronic properties arise from the [CuTS 3 ] – layers and show surprisingly little dependence on the interlayer distance.

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

Orientation-dependent mutual crystalline and amorphous order in a single phase solid

Amorphous materials distinguish themselves from crystalline materials by lacking long-range order while retaining structural order at the local scale (2–5 Å). However, the complexity in topological and chemical order prevents current characterization tools from fully unveiling the structure in disordered materials. Consequently, the nature of medium-range order in amorphous materials has remained elusive. The Zachariasen and crystal competing models have been proposed to describe disordered phases and have both been verified through synthesis and characterization. The main difference between them is thought to be whether the amorphous phase shows medium-range order. Here we demonstrate a form of organized inorganic matter that is amorphous in two dimensions, while exhibiting long-range order and a high degree of crystallinity in the third. The structure consists of periodically stacked 2-dimensional amorphous Nb-W-O monolayers without long-range in-plane order. The unique periodic and therefore crystalline stacking along one principal axis enables direct imaging and revealed that the amorphous Nb-W-O monolayers formed in agreement with the Zachariasen model for 2 dimensions. Our findings show that the gap between crystalline and amorphous materials does not only depend on medium-range order but can also apply to principal dimensions within the same solid.

Nanowires↗
NASA NTRS1973

Oxidation of organic molecules by photoproduced holes of ZnO.

Two experimental techniques were developed. In the first, an electrochemical method was used with a single crystal ZnO electrode and with the material of interest dissolved in the electrolyte. In the other an electron spin resonance method was used so that measurements related to thermal control coatings could be made with the ZnO in the form of powder, either alone or in formulation of a binder. A simplified model regarding the relationship between the electron density and time is considered.

Sancier, K. M.↗
NASA NTRS1985

Crystal Growth Research in Space

The objectives of this work are to develop growth techniques and theory leading to improved bulk growth of semiconductor single crystals. Ground based experiments will be complemented by experiments carried out in the low-g environment provided by the space shuttle. Analytical studies and laboratory investigations are being conducted to better define the causes of crystalline defects and inhomogeneities. The compound semiconductor lead-tin-telluride is being used as the modeling material. Theoretical techniques are being developed to predict the thermal and solutal fields which are present during bulk growth from a melt. Techniques for measuring the thermophysical properties of semiconductors at high temperatures have been developed. During the past year electrochemical etching techniques have been developed for delineation of inhomogeneous regions in crystals. Thermal diffusivity measurements have been completed for the solid and liquid phases of PbTe and PbSnTe. Preliminary results have been obtained on the effects on crystal morphology of gravity, interface shape and interaction between the melt and the container.

Crouch, R. K.↗
DOE OSTI2023

One-bond 13 C– 13 C spin-coupling constants in saccharides: a comparison of experimental and calculated values by density functional theory using solid-state 13 C NMR and X-ray crystallography

Methyl aldohexopyranosides were 13 C-labeled at contiguous carbons, crystallized, and studied by single-crystal X-ray crystallography and solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy to examine the degree to which density functional theory (DFT) can calculate one-bond 13C–13C spin-coupling constants ( 1 J CC ) in saccharides with sufficient accuracy to permit their use in MA'AT analysis, a newly-reported hybrid DFT/NMR method that provides probability distributions of molecular torsion angles in solution (Zhang et al., J. Phys. Chem. B, 2017, 121, 3042–3058; Meredith et al., J. Chem. Inf. Model., 2022, 62, 3135–3141). Experimental 1 J CC values in crystalline samples of the doubly 13 C-labeled compounds were measured by solid-state 13 C NMR and compared to those calculated from five different DFT models: (1) 1 J CC values calculated from single structures identical to those observed in crystalline samples by X-ray crystallography (all atom refinement); (2) 1 J CC values calculated from the single structures in (1) but after Hirshfeld atom refinement (HAR); (3) 1 J CC values calculated from the single structures in (1) after DFT-optimization of hydrogen atoms only; and (4 and 5) 1 J CC values calculated in rotamers of torsion angle θ 2 (C1–C2–O2–O2H) or ω(C4–C5–C6–O6) from which either specific or generalized parameterized equations were obtained and used to calculate 1 J CC values in the specific θ 2 or ω rotamers observed in crystalline samples. Good qualitative agreement was observed between calculated 1 J CC values and those measured by solid-state 13 C NMR regardless of the DFT model, but in no cases were calculated 1 J CC values quantitative, differing (over-estimated) on average by 4–5% from experimental values. These findings, and those reported recently from solution NMR studies (Tetrault et al., J. Phys. Chem. B 2022, 126, 9506–9515), indicate that improvements in DFT calculations are needed before calculated 1 J CC values can be used directly as reliable constraints in MA'AT analyses of saccharides in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗