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At least 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Novel Theoretical Prediction of Structural Properties, Ferromagnetic Ordering, and Electronic Structure of Fe{sub 2}PbC MAX Phase

In this study, we have investigated the magnetic stability; ferromagnetic ordering; and structural, elastic, and electronic properties of Fe{sub 2}PbC compound. The calculations are performed by the use of full-potential linearized augmented plane wave method implemented in WIEN2k code. We have found that the ferromagnetic state of Fe{sub 2}PbC is more stable than non-magnetic state configuration at their equilibrium lattice parameters. The structural and elastic properties suggest that Fe{sub 2}PbC is an anisotropic material, which is stable in the hexagonal MAX phase. The electronic structures show that Fe{sub 2}PbC has metallic-covalent-ionic character. The ferromagnetic performance of Fe{sub 2}PbC is confirmed by the total magnetic moment of 4.15 μ{sub B}, where its main contribution is originated from Fe atoms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Crystal structure of glycoside hydrolase family 127 β-L-arabinofuranosidase from Bifidobacterium longum

Graphical abstract: - Highlights: • HypBA1 β-L-arabinofuranosidase belongs to glycoside hydrolase family 127. • Crystal structure of HypBA1 was determined. • HypBA1 consists of a catalytic barrel and two additional β-sandwich domains. • The active site contains a Zn{sup 2+} coordinated by glutamate and three cysteines. • A possible reaction mechanism involving cysteine as the nucleophile is proposed. - Abstract: Enzymes acting on β-linked arabinofuranosides have been unknown until recently, in spite of wide distribution of β-L-arabinofuranosyl oligosaccharides in plant cells. Recently, a β-L-arabinofuranosidase from the glycoside hydrolase family 127 (HypBA1) was discovered in the newly characterized degradation system of hydroxyproline-linked β-L-arabinooligosaccharides in the bacterium Bifidobacterium longum. Here, we report the crystal structure of HypBA1 in the ligand-free and β-L-arabinofuranose complex forms. The structure of HypBA1 consists of a catalytic barrel domain and two additional β-sandwich domains, with one β-sandwich domain involved in the formation of a dimer. Interestingly, there is an unprecedented metal-binding motif with Zn{sup 2+} coordinated by glutamate and three cysteines in the active site. The glutamate residue is located far from the anomeric carbon of the β-L-arabinofuranose ligand, but one cysteine residue is appropriately located for nucleophilic attack for glycosidic bond cleavage. The residues around the active site are highly conserved among GH127 members. Based on biochemical experiments and quantum mechanical calculations, a possible reaction mechanism involving cysteine as the nucleophile is proposed.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Measurements of structures and concentrations of carbon particle species in premixed flames by the use of in-situ wide angle X-ray scattering

In-situ wide-angle X-ray scattering (WAXS) measurements have been conducted on atmospheric-pressure fuel-rich premixed freely propagating ethylene/oxygen flames with argon and nitrogen dilution. In this work, a novel analysis methodology able to provide quantitative information on soot/carbon particle species and concentrations was tested under heavy sooting conditions. The particle composition and concentrations were retrieved by fitting theoretical calculations of structural components from major molecular and nanometric species to the experimental WAXS data. The results show that argon dilution yields predominantly graphenelike components that are less stacked and amorphous carbon that is less structured than under nitrogen dilution. This finding was later confirmed by electron microscopy analysis on samples extracted from similar flames. In addition, the WAXS showed that most of the carbon present in the flames was bound as particles. These results constitute some of the first in-situ observations on structures and concentrations of carbon species in laboratory burner flames operating without stabilization plates.

Concentrations↗
DOE OSTI2011

Structural Basis for Promoter ;#8722;10 Element Recognition by the Bacterial RNA Polymerase [sigma] Subunit

The key step in bacterial promoter opening is recognition of the -10 promoter element (T-{sub 12}A-{sub 11}T-{sub 10}A-{sub 9}A-{sub 8}T{sub -7} consensus sequence) by the RNA polymerase {alpha} subunit. We determined crystal structures of {alpha} domain 2 bound to single-stranded DNA bearing -10 element sequences. Extensive interactions occur between the protein and the DNA backbone of every -10 element nucleotide. Base-specific interactions occur primarily with A{sub -11} and T{sub -7}, which are flipped out of the single-stranded DNA base stack and buried deep in protein pockets. The structures, along with biochemical data, support a model where the recognition of the -10 element sequence drives initial promoter opening as the bases of the nontemplate strand are extruded from the DNA double-helix and captured by {alpha}. These results provide a detailed structural basis for the critical roles of A{sub -11} and T{sub -7} in promoter melting and reveal important insights into the initiation of transcription bubble formation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Impact load-induced micro-structural damage and micro-structure associated mechanical response of concrete made with different surface roughness and porosity aggregates

The relationship between the nature of micro damage under impact loading and changes in mechanical behavior associated with different microstructures is studied for concretes made with two different coarse aggregates having significant differences mainly in roughness and porosity - sintered fly ash and uncrushed gravel. A range of techniques including X-ray diffraction, digital image analysis, mercury porosimetry, X-ray computed tomography, laser surface profilometry and scanning electron microscopy were used to characterize the aggregates and micro-structures. The concrete prepared with lightweight aggregates was stronger in compression than the gravel aggregate concrete due to enhanced hydration as a result of internal curing. In the lightweight concrete, it was deduced that an inhomogeneous micro-structure led to strain incompatibilities and consequent localized stress concentrations in the mix, leading to accelerated failure. The pore structure, compressibility, and surface texture of the aggregates are of paramount importance for the micro-cracking growth.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A numerical approach for simulating fluid structure interaction of flexible thin shells undergoing arbitrarily large deformations in complex domains

We present a new numerical methodology for simulating fluid–structure interaction (FSI) problems involving thin flexible bodies in an incompressible fluid. The FSI algorithm uses the Dirichlet–Neumann partitioning technique. The curvilinear immersed boundary method (CURVIB) is coupled with a rotation-free finite element (FE) model for thin shells enabling the efficient simulation of FSI problems with arbitrarily large deformation. Turbulent flow problems are handled using large-eddy simulation with the dynamic Smagorinsky model in conjunction with a wall model to reconstruct boundary conditions near immersed boundaries. The CURVIB and FE solvers are coupled together on the flexible solid–fluid interfaces where the structural nodal positions, displacements, velocities and loads are calculated and exchanged between the two solvers. Loose and strong coupling FSI schemes are employed enhanced by the Aitken acceleration technique to ensure robust coupling and fast convergence especially for low mass ratio problems. The coupled CURVIB-FE-FSI method is validated by applying it to simulate two FSI problems involving thin flexible structures: 1) vortex-induced vibrations of a cantilever mounted in the wake of a square cylinder at different mass ratios and at low Reynolds number; and 2) the more challenging high Reynolds number problem involving the oscillation of an inverted elastic flag. For both cases the computed results are in excellent agreement with previous numerical simulations and/or experiential measurements. Grid convergence tests/studies are carried out for both the cantilever and inverted flag problems, which show that the CURVIB-FE-FSI method provides their convergence. Finally, the capability of the new methodology in simulations of complex cardiovascular flows is demonstrated by applying it to simulate the FSI of a tri-leaflet, prosthetic heart valve in an anatomic aorta and under physiologic pulsatile conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Synthesis Structure and Characterization of the n=4 Aurivillius Phase Bi5Ti3CrO15

The n=4 Aurivillius phase, Bi{sub 5}Ti{sub 3}CrO{sub 15}, was synthesized by solid state reaction. Rietveld analysis of high resolution neutron diffraction data demonstrated this material to adopt the polar space group A2{sub 1}am at room temperature, transforming to the aristotype I4/mmm structure above 650 C. This phase transition is coincident with an anomaly in DSC signal and relative permittivity, which are characteristic of a ferroelectric-paraelectric phase transition. Bi{sub 5}Ti{sub 3}CrO{sub 15} exhibits paramagnetic behavior at low temperature, with short range antiferromagnetic interactions, but no evidence for long range magnetic ordering. This is considered a consequence of significant disorder of Ti and Cr over the available octahedral sites, as demonstrated by analysis of neutron diffraction data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Crystal structure analysis of tungsten bronzes {beta}-SrTa{sub 2}O{sub 6} and {beta} Prime -SrTa{sub 2}O{sub 6} by synchrotron X-ray and neutron powder diffraction

Strontium ditantalum oxide SrTa{sub 2}O{sub 6} exists in {alpha}-, {beta}-, and {beta} Prime -polymorphs. Herein the crystal structures of the latter two were studied using synchrotron X-ray and constant-wavelength neutron powder diffraction. While {beta} Prime -SrTa{sub 2}O{sub 6} [space group P4/mbm, a=12.47099(1) A, c=3.898210(5) A, V=606.271(2) Angstrom-Sign {sup 3}, Z=5] belongs to the regular tetragonal tungsten bronze (TTB) family, it contains locally disordered strontium atoms within the pentagonal channel. {beta}-SrTa{sub 2}O{sub 6} [space group Pnam, a=12.36603(2) Angstrom-Sign , b=12.43467(2) A, c=7.72403(1) A, V=1187.705(4) Angstrom-Sign {sup 3}, Z=10] can be described as an orthorhombic modification of the TTB, where the octahedral tilting distortion effectively alleviates the bonding strains around TaO{sub 6} and SrO{sub 13} polyhedra. For comparison, rynersonite type {alpha}-SrTa{sub 2}O{sub 6} [space group Pnma, a=11.00610(6) Angstrom-Sign , b=7.63397(3) Angstrom-Sign , c=5.62634(3) Angstrom-Sign , V=472.727(5) Angstrom-Sign {sup 3}, and Z=4] is built from edge-shared dimer units of TaO{sub 6} octahedra. As measured by diffuse-reflection absorption spectroscopy, {alpha}-, {beta}-, and {beta} Prime -SrTa{sub 2}O{sub 6} have indirect band gap energies of 4.4, 4.0, and 3.8 eV, respectively. - Graphical Abstract: Difference Fourier map for {beta} Prime -SrTa{sub 2}O{sub 6} at z=0. Highlights: Black-Right-Pointing-Pointer Structure refinements of {beta}-SrTa{sub 2}O{sub 6} and {beta} Prime -SrTa{sub 2}O{sub 6}. Black-Right-Pointing-Pointer Strontium disorder in tetragonal tungsten bronze {beta} Prime -SrTa{sub 2}O{sub 6}. Black-Right-Pointing-Pointer Orthorhombic distortion and cell doubling in {beta}-SrTa{sub 2}O{sub 6}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Structure and physical properties of single crystal PrCr{sub 2}Al{sub 20} and CeM{sub 2}Al{sub 20} (M=V, Cr): A comparison of compounds adopting the CeCr{sub 2}Al{sub 20} structure type

Crystal growth and full structure determination of compounds adopting the CeCr{sub 2}Al{sub 20} structure type, LnTi{sub 2}Al{sub 20} (Ln=La-Pr, Sm, and Yb), LnV{sub 2}Al{sub 20} (Ln=La-Pr, and Sm), and LnCr{sub 2}Al{sub 20} (Ln=La-Pr, Sm, and Yb), are reported. Resistivity, magnetic susceptibility, and heat capacity of flux grown single crystals of the nonmagnetic CeM{sub 2}Al{sub 20} (Ln=Ce, Yb; M=Ti, V) compounds are compared to PrCr{sub 2}Al{sub 20}. Of particular interest is PrCr{sub 2}Al{sub 20} which does not show any phase transition down to the lowest temperature of the measurement (400 mK in resistivity measurement and 1.8 K for magnetic susceptibility measurements) and exhibits Kondo behavior at low temperatures. - Graphical abstract: Crystal structure of SmV{sub 2}Al{sub 20} showing the interpenetrating diamond-like samarium network and pyrochlore-like vanadium network. Highlights: Black-Right-Pointing-Pointer Single crystals of LnM{sub 2}Al{sub 20} were grown from a molten aluminum flux. Black-Right-Pointing-Pointer Magnetic, electrical, and specific heat of single crystal LnM{sub 2}Al{sub 20} are presented. Black-Right-Pointing-Pointer PrCr{sub 2}Al{sub 20} exhibits evidence of Kondo effect.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis, structures of four coordination compounds constructed from o-methacrylamidobenzoic acid and their relationship between structure and solid state luminescence

Four new coordination compounds, namely, Zn(o-MAABA){sub 2}(Phen) (1), [Cd(o-MAABA){sub 2}·2H{sub 2}O]{sub 2} (2), ([Pb{sub 2}Cl{sub 2}(o-MAABA){sub 2}(Phen){sub 4}])·2H{sub 2}O (3·2H{sub 2}O), [Pb(NO{sub 3})(o-MAABA)(Phen)]{sub n} (4), where o-MAABA=o-methacrylamidobenzoic acid and phen=1, 10-phenanthroline, have been synthesized. All compounds were fully confirmed by FT-IR, elemental analysis and TGA analysis. Their structures were determined by single crystal X-ray diffraction, in which compound 1 shows a mononuclear structure, compounds 2 and 3 have binuclear structures and compound 4 shows an infinite chain. In 2 and 4, the adjacent chains are extended into a 3D supramolecular architecture via π–π interactions. Solid-state room temperature luminescence spectra revealed that emission bands of compound 1 were located at 524 nm (λ{sub ex}=352 nm) and compound 4 at 479 and 584 nm (λ{sub ex}=390 nm) assigned to the excimer formation. The emission at 454 nm (λ{sub ex}=340 nm) of compound 2 was mainly ascribed to the Ligand–Metal Charge Transfer (LMCT). - Graphical abstract: Four coordination compounds constructed by o-methacrylamidobenzoic, phenanthroline and metal ions are reported. The photoluminescent properties is studied, which is affected by the molecular stacking and LMCT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

New hybrid lead iodides: From one-dimensional chain to two-dimensional layered perovskite structure

Two new hybrid lead halides (H{sub 2}BDA)[PbI{sub 4}] (1) (H{sub 2}BDA=1,4-butanediammonium dication) and (HNPEIM)[PbI{sub 3}] (2) (HNPEIM=N-​phenyl-ethanimidamidine cation) have been synthesized and structurally characterized. X-ray diffraction analyses reveal that compound 1 features a two-dimensional corner-sharing perovskite layer whereas compound 2 contains one-dimensional edge-sharing double chains. The N-​phenyl-ethanimidamidine cation within compound 2 was generated in-situ under solvothermal conditions. The optical absorption spectra collected at room temperature suggest that both compounds are semiconductors having direct band gaps, with estimated values of 2.64 and 2.73 eV for 1 and 2, respectively. Results from the density functional theory (DFT) calculations are consistent with the experimental data. Density of states (DOS) analysis reveals that in both compounds 1 and 2, the energy states in the valence band maximum region are iodine 5p atomic orbitals with a small contribution from lead 6s, while in the region of conduction band minimum, the major contributions are from the inorganic (Pb 6p atomic orbitals) and organic components (C and N 2p atomic orbitals) in compound 1 and 2, respectively. - Graphical abstract: Two new hybrid lead halides built on one-dimensional edge-sharing double chains and two-dimensional corner-sharing perovskite layers are synthesized and their structural and electronic properties are analyzed. - Highlights: • Two new hybrid lead iodides are designed, synthesized, and characterized. • They are closely related to, but different from, perovskite structures. • The electronic properties of both compounds are analyzed by DFT calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Synthesis, crystal structure, optical, and electronic study of the new ternary thorium selenide Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2}

The compound Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. Each Th atom in these chains is coordinated to two Se–Se single-bonded pairs and four Se atoms to give rise to a pseudooctahedral geometry around Th. The Th–Se distances are consistent with Th{sup 4+} and hence charge balance of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is achieved as 3×Ba{sup 2+}, 1×Th{sup 4+}, 3×Se{sup 2−}, and 2×Se{sub 2}{sup 2−}. From optical measurements the band gap of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor. - Graphical abstract: Local coordination environment of Th atoms in the Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} structure. - Highlights: • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. • The structure features chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is a semiconductor with a band gap of 1.96(2) eV.

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

Syntheses, crystal Structures and electronic Structures of new metal chalcoiodides Bi{sub 2}CuSe{sub 3}I and Bi{sub 6}Cu{sub 3}S{sub 10}I

Two new metal chalcoiodides were synthesized by solid-state reactions at 400 °C. Crystal Data: Bi{sub 2}CuSe{sub 3}I, 1, monoclinic, C2/m, a=14.243(2) Å, b=4.1937(7) Å, c=14.647(2) Å, β=116.095(2)°, V=785.7(2) Å{sup 3}, and Z=4; Bi{sub 6}Cu{sub 3}S{sub 10}I, 2, orthorhombic, Pnma, a=17.476(2) Å, b=4.0078(4) Å, c=27.391(2) Å, V=1918.5(3) Å{sup 3}, and Z=4. Compound 1 adopts a three-dimensional structure formed by two alternative layers, which consist of BiSe{sub 5} square pyramids, BiSe{sub 4}I{sub 2} octahedra, CuSe{sub 4} tetrahedra, and CuSe{sub 2}I{sub 2} tetrahedra. Compound 2 possesses a new open framework built up of BiS{sub 5} square pyramides, BiS{sub 6} octahedra, BiS{sub 8} polyhedra, and CuS{sub 4} tetrahedra where I{sup −} anions are uniquely trapped within the tunnels. Both electronic structures reveal that bismuth and chalcogenide orbitals dominate the bandgaps. The Cu d and I p states contribute to the top of valence bands, in which the distribution of I orbitals may correspond to the relative bonding interactions in 1 and 2. The optical bandgaps determined by the diffuse reflectance spectra are 0.68 eV and 0.72 eV for 1 and 2, respectively. 1 is a p-type semiconductor with high Seebeck coefficients of 460–575 μV/K in the temperature range of 300–425 K. The electrical conductivity is 0.02 S/cm at 425 K for the undoped sample. The thermal conductivity is 0.22 W/mK at 425 K. - Graphical abstract: The hybridization of chalcogenides and iodides produces two new solids Bi2CuSe3I and Bi6Cu3S10I. The I{sup −} anions participate in distinct bonding interactions within the two structures and that is consistent with the analyses of density of states. 1 is a p-type semiconductor with an optical bandgap of 0.68 eV, which possesses high Seebeck coefficient and low lattice thermal conductivity in 300–425 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Copper coordination polymers constructed from thiazole-5-carboxylic acid: Synthesis, crystal structures, and structural transformation

We have successfully prepared crystals of thiazole-5-carboxylic acid (5-Htza) (L) and three new thiazole-5-carboxylate-based Cu{sup 2+} coordination polymers with different dimensionality, namely, 1D [Cu{sub 2}(5-tza){sub 2}(1,10-phenanthroline){sub 2}(NO{sub 3}){sub 2}] (1), 2D [Cu(5-tza){sub 2}(MeOH){sub 2}] (2), and 3D [Cu(5-tza){sub 2}]·H{sub 2}O (3). These have been characterized by single crystal X-ray diffraction and thermogravimetry. Interestingly, the 2D network structure of 2 can directly transform into the 3D framework of 3 upon removal of methanol molecules at room temperature. 2 can also undergo structural transformation to produce the same 2D network present in the known [Cu(5-tza){sub 2}]·1.5H{sub 2}O upon heat treatment for 2 h. This 2D network can adsorb water and convert to 3 upon exposure to air. - Highlights: • Rare examples of coordination polymers of thiazole-5-carboxylic acid were prepared. • Non-covalent interactions play a key role on the assembly of the complexes in solid state. • Structural transformation of a 2D framework to a 3D upon removal of methanol is observed.

36 MATERIALS SCIENCE↗