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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Structural transformation features in titanium crystallite under mechanical loading

The features of defect structure generation and development in titanium crystallites were studied on the basis of molecular dynamics method. Interatomic interaction was described using many-body potentials calculated in the approximation of the embedded atom method. It is shown that local structural changes begin to occur in the crystallite at the achievement of a threshold strain value, which is accompanied by a dramatic decrease of potential energy. The features of the formation of local structural changes, which are precursors of classical stacking faults, were studied.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Evolution of nontrivial Fermi surface features in the band structures of the homologous members Pb 5 Bi 6 Se 14 and Pb 5 Bi 12 Se 23

High-quality single crystals of (PbSe) 5 (Bi 2 Se 3 ) 3m were grown and analyzed by nuclear magnetic resonance (NMR) spectroscopy. We report on 77 Se and 207 Pb NMR shifts and nuclear spin-lattice relaxation measurements in the naturally formed heterostructure homology (PbSe) 5 (Bi 2 Se 3 ) 3m with m = 1 (Pb 5 Bi 6 Se 14 ) and m = 2 (Pb 5 Bi 12 Se 23 ). A distinct site-specific contribution has been detected for both nuclei as a function of temperature, which reveals an electronic changeover from a semiconducting (Pb 5 Bi 6 Se 14 ) to a semimetalliclike (Pb 5 Bi 12 Se 23 ) system with nontrivial band structure features near the Fermi level. The temperature dependences of the relaxation rates are dominated by significant changes in the topology of energy dispersions accompanied with band edges and crossings in the region of the Fermi surface. These results, which interrogate nuclear spin interactions from selected atomic sites, clearly expose the effects of the added Bi 2 Se 3 layer on the crystal and electronic structure of (Pb 5 Bi 12 Se 23 ). These findings provide direct microscopic insight into the unconventional and dual nature of the electronic structure of these homologous thermoelectric and topologically nontrivial compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

An X-ray and Neutron Scattering Study of the Formation of Core-Shell Type Polyoxometalates

A typical type of core-shell polyoxometalates can be obtained through the Keggin-type polyoxometalatetemplated growth of a layer of spherical shell structure of {Mo72Fe30}. Small angle X-ray scattering is used to study the structural features and stability of the core-shell structures in aqueous solutions. Timeresolved small angle X-ray scattering is applied to monitor the synthetic reactions and a three-stage formation mechanism is proposed to describe the synthesis of the core-shell polyoxometalates based on the monitoring results. New protocols have been developed by fitting the X-ray data with customed physical models, which provide more convincing, objective, and completed data interpretation. Quasielastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core-shell structures and two different types of water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures.

Yin, Panchao↗
DOE OSTI2016

An in-depth understanding of biomass recalcitrance using natural poplar variants as the feedstock

Here, in an effort to better understand the biomass recalcitrance, six natural poplar variants were selected as feedstocks based on previous sugar release analysis. Compositional analysis and physicochemical characterizations of these poplars were performed and the correlations between these physicochemical properties and enzymatic hydrolysis yield were investigated. Gel permeation chromatography (GPC) and 13 C solid state NMR were used to determine the degree of polymerization (DP) and crystallinity index (CrI) of cellulose, and the results along with the sugar release study indicated that cellulose DP likely played a more important role in enzymatic hydrolysis. Simons’ stain revealed that the accessible surface area of substrate significantly varied among these variants from 17.3 to 33.2 mg g$–1\atop{biomass}$ as reflected by dye adsorption, and cellulose accessibility was shown as one of the major factors governing substrates digestibility. HSQC and 31 P NMR analysis detailed the structural features of poplar lignin variants. Overall, cellulose relevant factors appeared to have a stronger correlation with glucose release, if any, than lignin structural features. Lignin structural features, such as a phenolic hydroxyl group and the ratio of syringyl and guaiacyl (S/G), were found to have a more convincing impact on xylose release. Low lignin content, low cellulose DP, and high cellulose accessibility generally favor enzymatic hydrolysis; however, recalcitrance cannot be simply judged on any single substrate factor.

09 BIOMASS FUELS↗
DOE OSTI2019

Quantitative Structure–Property Relationship (QSPR) Analysis of ZrO 2 -Containing Soda-Lime Borosilicate Glasses

Quantitative structure–property relationship (QSPR) analysis is a promising approach to correlate structural features with properties of glass materials that lack long-range order and usually have complex structures. By using carefully chosen descriptors based on structural models generated from molecular dynamics (MD) simulations, correlations with properties and insights on glass behaviors can be obtained. Zirconia can significantly alter glass properties including chemical durability, even in a small amount, and hence plays an important role in vitrification of nuclear waste where long-term chemical durability is desired. In this study, borosilicate glasses with the composition of xZrO 2 –(61 – x)SiO 2 –17B 2 O 3 –18Na 2 O–4CaO with x = 0, 1, 2, 4, 6, and 8 were simulated using classical MD simulations with the recently developed composition-dependent potentials. Short-range (e.g., bond distance and coordination numbers) and medium-range (e.g., Qn distribution, network connectivity, and ring-size distribution) structural features altered by ZrO 2 were obtained and analyzed. The use of a descriptor (Fnet descriptor) that combines short-range structural characteristics, from MD simulations, and the cation-oxygen single bond strength was found to provide excellent linear correlations with the density and initial dissolution rate of these glasses. Furthermore, the results show that by combining MD simulations and QSPR analysis the composition and structural effect on the properties of complex multicomponent glasses can be elucidated, thus suggesting that this is a promising approach for future glass research and new composition design.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Micrometre-scale single-crystalline borophene on a square-lattice Cu(100) surface

Borophene, a crystalline monolayer boron sheet, is a new two-dimensional (2D) quantum material, predicted to feature tunable structure, intriguing physics and to find applications in flexible electronics, energy storage and catalysis. Nanoscale borophene flakes have been synthesized on noble-metal surfaces, but for device fabrication, one needs large single-crystal domains. In this work, we report the synthesis of borophene on a square lattice Cu(100) surface and show that incommensurate coordinations could reduce the borophene-substrate interactions and alter the borophene structures in interesting ways. Micrometer-scale single-crystal domains can form as isolated faceted islands or merge together to achieve full monolayer coverage. We have discovered a new crystal structure of borophene, with ten boron atoms and two hexagonal vacancies in the unit cell. First-principle calculations indicate that charge transfer rather than covalent bonding binds 2D boron to the copper surface, and confirm its integrity and uniformity The electronic band structure features multiple anisotropic tilted Dirac cones, heralding emergent quantum fermions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Features of the Formation and Structure of Barium Titanate Langmuir Films

Ferroelectric films of stabilized barium titanate nanoparticles have been obtained from the colloidal system of a sodium oleate aqueous solution by the Langmuir–Blodgett method at the KSV NIMA 2002 facility, coagulants with the most characteristic hydrodynamic diameter of ∼200 nm have been found, and a physical model of their formation from barium titanate nanoparticles in this colloid system has been proposed. Homogeneous ferroelectric films with barium titanate particles ∼20 nm in size and a band gap of 3.6 eV have been deposited. The topological and structural features and distribution of chemical elements in the obtained films on different substrates have been studied by the methods of scanning probe and electron microscopy, vibrational and X-ray photoelectron spectroscopy, as well as X-ray diffractometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Modeling Fission Product Sorption in Graphite Structures

The goal of this project is to determine changes in adsorption and desorption of fission products to/from nuclear-grade graphite in response to a changing chemical environment. First, the project team will employ principle calculations and thermodynamic analysis to predict stability of fission products on graphite in the presence of structural defects commonly observed in very high- temperature reactor (VHTR) graphites. Desorption rates will be determined as a function of partial pressure of oxygen and iodine, relative humidity, and temperature. They will then carry out experimental characterization to determine the statistical distribution of structural features. This structural information will yield distributions of binding sites to be used as an input for a sorption model. Sorption isotherms calculated under this project will contribute to understanding of the physical bases of the source terms that are used in higher-level codes that model fission product transport and retention in graphite. The project will include the following tasks: Perform structural characterization of the VHTR graphite to determine crystallographic phases, defect structures and their distribution, volume fraction of coke, and amount of sp2 versus sp3 bonding. This information will be used as guidance for ab initio modeling and as input for sorptivity models; Perform ab initio calculations of binding energies to determine stability of fission products on the different sorption sites present in nuclear graphite microstructures. The project will use density functional theory (DFT) methods to calculate binding energies in vacuum and in oxidizing environments. The team will also calculate stability of iodine complexes with fission products on graphite sorption sites; Model graphite sorption isotherms to quantify concentration of fission products in graphite. The binding energies will be combined with a Langmuir isotherm statistical model to predict the sorbed concentration of fission products on each type of graphite site. The model will include multiple simultaneous adsorbing species, which will allow for competitive adsorption effects between different fission product species and O and OH (for modeling accident conditions).

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

Compositional control of radionuclide retention in hollandite-based ceramic waste forms for Cs-immobilization

Hollandite materials, as a class of crystalline nuclear waste forms, are promising candidates for the immobilization of radioactive elements, such as Cs, Ba, as well as a variety of lanthanide and transition-metal fission products. In this study, three Ga-doped titanate hollandite-type phases, Ba 1.33 Ga 2.67 Ti 5.33 O 16 , Ba 0.667 Cs 0.667 Ga 2 Ti 6 O 16 , and Cs 1.33 Ga 1.33 Ti 6.67 O 16 , were synthesized using a solid-state reaction route. All synthesized phases adopted a single phase tetragonal structure, as determined by powder X-ray diffraction (XRD), and elemental analysis confirmed the measured stoichiometries were close to targeted compositions. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local structural features for the framework of octahedrally coordinated cations. EXAFS data indicated that Cs 1.33 Ga 1.33 Ti 6.67 O 16 possessed the most disordered local structure centered around the Ga dopant. The enthalpies of formation of all three hollandite phases measured using high-temperature oxide melt solution calorimetry were found to be negative, indicating enthalpies of formation of these hollandites from oxides are thermodynamically stable with respect to their constituent oxides. Furthermore, the formation enthalpies were more negative and hence more favorable with increased Cs content. Finally, aqueous leaching tests revealed that high Cs content hollandite phases exhibited greater Cs retention as compared to low Cs content hollandite. While preliminary in nature, this work draws attention to the links between the capacity for radionuclide retention, atomistic level structural features and bulk thermodynamic properties of materials.

nuclear (including radiation effects), materials a↗
DOE OSTI2016

Structural diversity and fluorescence properties of three 2-sulfoterephthalate Cd{sup II}/Zn{sup II} coordination polymers employing 1,4-bisbenzimidazole

Three novel coordination polymers, namely, [Cd(2-Hstp)(1,4-bbi)(H{sub 2}O){sub 2}]·3H{sub 2}O (1), [Cd{sub 1.5}(2-stp)(1,4-bbi)(H{sub 2}O){sub 2}]·H{sub 2}O (2) and [Zn{sub 2}(2-stp)(μ{sub 2}-OH)(1,4-bbi){sub 1.5}(H{sub 2}O)]·6H{sub 2}O (3) (2-H{sub 3}stp is equal to 2-sulfoterephthalate and 1,4-bisbenzimidazole is equal to 1,4-bbi), have been synthesized by hydrothermal reaction. The structural analyses show that 1 and 2 possess different structural features despite the same raw materials, which are 1D chain structure featuring 6-member-water H-bonds cluster and 3D bbi-pillared wavy-like layer framework, respectively. As changing the metal ion to zinc ion, 3 exhibits 3D stp-pillared layer architecture, which discovers the effect of the central metal ions on the formation of metal–organic frameworks. The fluorescence studies show that the emissions of the coordination polymers are attributed to the ligand π–π* transition, which means they could be potential fluorescence materials. - Graphical abstract: Three new Cd{sup II}/Zn{sup II} 2-sulfoterephthalate (2-H{sub 3}stp) complexes with 1,4-bisbenzimidazole (1,4-bbi) are described. Complex 1 exhibits one-dimensional chain-like structure, 2 is a three-dimensional bbi-pillared wavy-like layer framework, while 3 is a three-dimensional stp-pillared layer architecture. Fluorescence spectra exhibit the π–π* transition of two organic ligands. - Highlights: • Three Cd{sup II}/Mn{sup II} 2-sulfoterephthalate complexes containing 1,4-bisbenzimidazole. • Different structural features despite the same raw materials for 1 and 2. • Fluorescence spectra exhibit the π–π* transition of organic ligands.

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

Three-dimensional structure of E. Coli purine nucleoside phosphorylase at 0.99 Å resolution

Purine nucleoside phosphorylases (PNPs) catalyze the reversible phosphorolysis of nucleosides and are key enzymes involved in nucleotide metabolism. They are essential for normal cell function and can catalyze the transglycosylation. Crystals of E. coli PNP were grown in microgravity by the capillary counterdiffusion method through a gel layer. The three-dimensional structure of the enzyme was determined by the molecular-replacement method at 0.99 Å resolution. The structural features are considered, and the structure of E. coli PNP is compared with the structures of the free enzyme and its complexes with purine base derivatives established earlier. A comparison of the environment of the purine base in the complex of PNP with formycin A and of the pyrimidine base in the complex of uridine phosphorylase with thymidine revealed the main structural features of the base-binding sites. Coordinates of the atomic model determined with high accuracy were deposited in the Protein Data Bank (PDB-ID: 4RJ2).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗