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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Intramolecular C—F→Ln dative interactions in lanthanide complexes with fluorinated ligands

Complexes reported in the literature and potentially capable of intramolecular C—F→Ln interactions were analyzed. It was proposed to use the ToposPro software for structural and topological analysis to search for intramolecular C—F→Ln interactions. The shortest detected Ln···F contact amounted to 2.374 Å, while the longest weak non-valence contact was 4.060 Å. For all lanthanide complexes with Ln···F distances shorter than 3.447 Å, only strong intramolecular (valence) interactions between these atoms were observed. These interactions can affect the physicochemical properties of complexes and they are to be taken into account in determination of the coordination environment of lanthanide atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Sulfur Removal by Adding Iron During the Digestion Process of High-sulfur Bauxite

This paper proposes a novel approach to sulfur removal by adding iron during the digestion process. Iron can react with high-valence sulfur (S{sub 2}O{sub 3}{sup 2−}, SO{sub 3}{sup 2−}, SO{sub 4}{sup 2−}) to generate S{sup 2−} at digestion temperature, and then S{sup 2−} enter red mud in the form of Na{sub 3}FeS{sub 3} to be removed. As iron dosage increases, high-valence sulfur concentration decreases, but the concentration of S{sup 2−} increases; sulfur digestion rate decreases while sulfur content in red mud markedly increases; the alumina digestion rate, conversely, remains fairly stable. So sulfur can be removed completely by adding iron in digestion process, which provide a theoretical basis for the effective removal of sulfur in alumina production process.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Isotope shifts in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations

Energy levels, normal and specific mass shift parameters as well as electronic densities at the nucleus are reported for numerous states along the beryllium, boron, carbon, and nitrogen isoelectronic sequences. Combined with nuclear data, these electronic parameters can be used to determine values of level and transition isotope shifts. The calculation of the electronic parameters is done using first-order perturbation theory with relativistic configuration interaction wavefunctions that account for valence, core–valence, and core–core correlation effects as zero-order functions. Results are compared with experimental and other theoretical values, when available.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Hyperfine structures and Landé g{sub J}-factors for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations

Energy levels, hyperfine interaction constants, and Landé g{sub J}-factors are reported for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations. Valence, core–valence, and core–core correlation effects are taken into account through single and double-excitations from multireference expansions to increasing sets of active orbitals. A systematic comparison of the calculated hyperfine interaction constants is made with values from the available literature.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

The S-matrix for surface boundary states: An application to photoemission for Weyl semimetals

We present a new theory of photoemission for Weyl semimetals. We derive this theory using a model with a boundary surface at z=0. Due to the boundary, the self adjoint condition needs to be verified in order to ensure physical solutions. The solutions are given by two chiral zero modes which propagate on the boundary. Due to the Coulomb interaction, the chiral boundary model is in the same universality class as interacting graphene. The interactions cause a temperature dependence of the velocity and life time. Using the principle of minimal coupling, we identify the electron–photon Hamiltonian. The photoemission intensity is computed using the S-matrix formalism. The S-matrix is derived using the initial photon state, the final state of a photoelectron and a hole in the valence band. The photoemission reveals the final valence band dispersion ħv(±k{sub y}−k{sub 0})+ħΩ after absorbing a photon of frequency Ω (k{sub 0} represents the shift in the momentum due to the crystal potential). The momentum in the z direction is not conserved, and is integrated out. As a result, the scattering matrix is a function of the parallel momentum . We observe two dimensional contours, representing the “Fermi arcs”, which for opposite spin polarization have opposite curvature. This theory is in agreement with previous experimental observations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Selenite and selenate uptaken in ettringite: Immobilization mechanisms, coordination chemistry, and insights from structure

Although ettringite is a crucial material in terms of Se immobilization, the immobilization mechanisms, atomic configuration, and intercolumn structure of Se sorbed in ettringite are unclear. The immobilization mechanism of Se oxoanions was evaluated through structural insight into ettringite. It is contrasting between SeO{sub 3}{sup 2−} and SeO{sub 4}{sup 2−} in chemical property of the solid residues after immobilization. The oxoanion exchange with structural SO{sub 4}{sup 2−} is the main mechanism for immobilization of SeO{sub 4}{sup 2−}. In contrast, SeO{sub 3}{sup 2−} is easily immobilized to form inner-sphere complexes in ettringite. In addition, it is necessary to reveal the SeO{sub 3}{sup 2−} complexation sites for understanding the mechanisms in immobilization of SeO{sub 3}{sup 2−}. Based on the characterization results with the bond valence theory, the location sites of sorbed SeO{sub 3}{sup 2−} in ettringite structure were proposed. The results obtained in this work are relevant to the understanding of Se and its isotopes immobilized in cement or alkaline environments, especially for nuclear waste management. - Highlights: • The immobilization mechanisms of SeO{sub 3}{sup 2−} and SeO{sub 4}{sup 2−} in ettringite are different. • Sorption of SeO{sub 3}{sup 2−} will remove structural water molecules in ettringite. • SeO{sub 3}{sup 2−} could form some inner-sphere complexes in the ettringite structure. • The EXAFS and bond valence theory was applied to determine the sorption mechanism. • The atomic configuration of ettringite surface was proposed after sorption of SeO{sub 3}{sup 2−}.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Hidden transformations in entropy-stabilized oxides

We report entropy-stabilized oxides (ESO) display a reversible entropy-driven phase transformation that can be leveraged to produce a continuum of metastable phase states, allowing for property optimization and novel functionalities. X-ray absorption spectroscopy reveals that entropic stabilization extends to the electronic structure (valence state and cation coordination) in sintered (Co,Cu,Mg,Ni,Zn)O, manifesting as a tunable lattice distortion in the entropy-stabilized phase. Co, Cu, and Zn ions reversibly transform from six-fold to four-fold coordinated structures and from low to high valence states due to the competition between electronic structures that are equilibrium and enthalpy-driven or metastable and entropy-driven. The segregation of a Cu-rich tenorite phase and a Co-rich spinel phase influences the electronic structure evolution. ESOs can adjust their electronic structures through heat treatment, providing a powerful tool for developing functional properties. These results indicate that the definition of entropy stabilization should include entropy-stabilized electronic structures, providing motivation to reassess previously studied HEO materials.

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

A family of rare earth molybdenum bronzes: Oxides consisting of periodic arrays of interacting magnetic units

The family of rare earth molybdenum bronzes, reduced ternary molybdates of composition LnMo{sub 16}O{sub 44,} was synthesized and a detailed structural study carried out. Bond valence sum (BVS) calculations clearly show that the molybdenum ions in tetrahedral coordination are hexavalent while the electron count in the primitive unit cell is odd. Yet, measurements show that the phases are semiconductors. The temperature dependence of the magnetic susceptibility of samples containing several different rare earth elements was measured. These measurements verified the presence of a 6.5 K magnetic phase transition not arising from the rare earth constituent, but likely associated with the unique isolated ReO{sub 3}-type Mo{sub 8}O{sub 36} structural subunits in this phase. To better understand the behavior of these materials, electronic structure calculations were performed within density functional theory. Results suggest a magnetic state in which these structural moieties have an internal ferromagnetic arrangement, with small ~1/8 μ{sub B} moments on each Mo. We suggest that the Mo{sub 8}O{sub 36} units behave like pseudoatoms with spin 1/2 derived from a single hole distributed over the eight Mo atoms that are strongly hybridized with the O atoms of the subunit. Interestingly, while the compound is antiferromagnetic, our calculations suggest that a field-stabilized ferromagnetic state, if achievable, will be a narrow band half-metal. - Graphical abstract: LnMo{sub 16}O{sub 44} phases comprise corner sharing tetrahedral and octahedral molybdenum ions. The MoO{sub 6} octahedra form Mo{sub 8}O{sub 36} units that are well separated and act like pseudo-atoms, accommodating 11 electrons each. - Highlights: • Single crystal X-ray diffraction refinements of LnMo{sub 16}O{sub 44} single crystals for Ln=Ce, Pr, Nd, Tb, Dy and Ho. • DFT calculations based on LaMo{sub 16}O{sub 44}. • [Mo{sub 8}O{sub 36}] units behaving as superatoms with a net magnetic moment of 1 µ{sub B}. • Bronze structure containing equal number of molybdenum tetrahedra and octahedral.

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

Synthesis of Zn–Fe layered double hydroxides via an oxidation process and structural analysis of products

The synthesis of Zn–Fe(III) layered double hydroxides was attempted, employing different pathways using either Fe(II) or Fe(III) species together with Zn as the initial reagents. The product derived from the synthesis employing Fe(II) was found to transition to a Zn–Fe(III) layered double hydroxides phase following oxidation process. In contrast, the product obtained with Fe(III) did not contain a layered double hydroxides phase, but rather consisted of simonkolleite and hydrous ferric oxide. It was determined that the valency of the Fe reagent used in the initial synthesis affected the generation of the layered double hydroxides phase. Fe(II) species have ionic radii and electronegativities similar to those of Zn, and therefore are more likely to form trioctahedral hydroxide layers with Zn species. - Graphical abstract: The synthesis of Zn–Fe(III) layered double hydroxides was attempted, employing different pathways using either Fe(II) or Fe(III) species together with Zn as the initial reagents. - Highlights: • Iron valency affected the generation of Zn–Fe layered double hydroxides. • Zn–Fe layered double hydroxides were successfully synthesized using Fe(II). • Fe(II) species were likely to form trioctahedral hydroxide layers with Zn species.

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

Structural investigations of Pu{sup III} phosphate by X-ray diffraction, MAS-NMR and XANES spectroscopy

PuPO{sub 4} was prepared by a solid state reaction method and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. High resolution XANES measurements confirm the +III valence state of plutonium, in agreement with valence bond derivation. The presence of the americium (as β{sup −} decay product of plutonium) in the +III oxidation state was determined based on XANES spectroscopy. High resolution solid state {sup 31}P NMR agrees with the XANES results and the presence of a solid-solution. - Graphical abstract: A full structural analysis of PuPO{sub 4} based on Rietveld analysis of room temperature X-ray diffraction data, XANES and MAS NMR measurements was performed. - Highlights: • The crystal structure of PuPO{sub 4} monazite is solved. • In PuPO{sub 4} plutonium is strictly trivalent. • The presence of a minute amount of Am{sup III} is highlighted. • We propose PuPO{sub 4} as a potential reference material for spectroscopic and microscopic studies.

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

First principle investigation of electronic structure, chemical bonding and optical properties of tetrabarium gallium trinitride oxide single crystal

The electronic band structure, valence electron charge density and optical susceptibilities of tetrabarium gallium trinitride (TGT) were calculated via first principle study. The electronic band structure calculation describes TGT as semiconductor having direct band gap of 1.38 eV. The valence electronic charge density contour verified the non-polar covalent nature of the bond. The absorption edge and first peak of dielectric tensor components showed electrons transition from N-p state to Ba-d state. The calculated uniaxial anisotropy (0.4842) and birefringence (−0.0061) of present paper is prearranged as follow the spectral components of the dielectric tensor. The first peak in energy loss function (ELOS) shows the energy loss of fast traveling electrons in the material. The first sharp peak produced in ELOS around 10.5 eV show plasmon loss having plasma frequencies 0.1536, 0.004 and 0.066 of dielectric tensor components. This plasmon loss also cause decrease in reflectivity spectra.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Enhancing visible light photocatalytic and photocharge separation of (BiO){sub 2}CO{sub 3} plate via dramatic I{sup −} ions doping effect

Highlights: • Novel I-(BiO){sub 2}CO{sub 3} was prepared by a facile chemical precipitation method. • I{sup −} ions impurity level located on the top of valence band of (BiO){sub 2}CO{sub 3}. • I{sup −} ions doping largely improved photocatalytic activity of I-(BiO){sub 2}CO{sub 3}. • I-(BiO){sub 2}CO{sub 3} displayed excellent photocharge separation efficiency. - Abstract: Novel I{sup −} ions doped (BiO){sub 2}CO{sub 3} (I-(BiO){sub 2}CO{sub 3}) photocatalysts were successfully synthesized via a facile chemical precipitation method. Under visible light (λ > 400 nm), I-(BiO){sub 2}CO{sub 3} displayed much higher activity for rhodamine B and dichlorophenol degradation than the undoped (BiO){sub 2}CO{sub 3}. The pseudo-first-order rate constant k{sub app} of RhB degradation over 15.0% I-(BiO){sub 2}CO{sub 3} was 0.54 h{sup −1}, which is 11.3 times higher than that of (BiO){sub 2}CO{sub 3}. The doped I{sup −} ions formed an impurity level on the top of valence band of (BiO){sub 2}CO{sub 3} and induced much more visible light to be absorbed. The enhanced photocurrent and surface photovoltage properties were detected, which strongly ensures the efficient separation of electrons and holes in I-(BiO){sub 2}CO{sub 3} system under visible light. It provides a facile way to improve the photocatalytic activity of the wide-band-gap (BiO){sub 2}CO{sub 3} via intense doping effect of I{sup −} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Elucidating the electronic structure of supported gold nanoparticles and its relevance to catalysis by means of hard X-ray photoelectron spectroscopy

We report on the electronic structure of Au (gold) nanoparticles supported onto TiO 2 with a goal of elucidating the most important effects that contribute to their high catalytic activity. We synthesize and characterize with high resolution transmission electron microscopy (HRTEM) 3.4, 5.3, and 9.5 nm diameter TiO 2 -supported Au nanoparticles with nearly spherical shape and measure their valence band using Au 5d subshell sensitive hard X-ray photoelectron spectroscopy (HAXPES) conducted at Spring-8. Based on density functional theory (DFT) calculations of various Au surface structures, we interpret the observed changes in the Au 5d valence band structure as a function of size in terms of an increasing percentage of Au atoms at corners/edges for decreasing particle size. Finally, this work elucidates how Au coordination number impacts the electronic structure of Au nanoparticles, ultimately giving rise to their well-known catalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Electrical conductivity of Sr{sub 2−x}VMoO{sub 6−y} (x = 0.0, 0.1, 0.2) double perovskites

Electrical conductivity of Sr{sub 2-x}VMoO{sub 6-y} (x = 0.0, 0.1, 0.2) double perovskites has been investigated in a reducing atmosphere at temperatures up to 800 °C. This material has a key application in solid oxide fuel cell anodes as a mixed ion and electron conductor. A solid state synthesis technique was used to fabricate materials and crystal structure was verified through x-ray diffraction. Subsequent to conventional sintering in a reducing environment, elemental valence states were indentified through x-ray photoemission spectroscopy on the double perovskite material before and after annealing in a hydrogen environment. Samples exhibited metallic like conduction with electrical conductivities of 1250 S/cm (Sr{sub 2}VMoO{sub 6-y′}), 2530 S/cm (Sr{sub 1.8}VMoO{sub 6-y″}), and 3610 S/cm (Sr{sub 1.9}VMoO{sub 6-y‴}) at 800 °C in 5% H{sub 2}/95% N{sub 2}, with a substantial increase in conductivity upon cooling to room temperature. Room temperature electrical conductivity values for Sr{sub 1.9}VMoO{sub 6-y‴} make it a candidate as the highest electrically conductive oxide known. Highly insulating secondary surface phases, Sr{sub 3}V{sub 2}O{sub 8}, and SrMoO{sub 4}, begin to reduce at 400 °C in a hydrogen environment, as confirmed by X-ray photoemission and thermal gravimetric analysis. This reduction, from V{sup 5+} and Mo{sup 6+} to lower valence states, leads to a large increase in sample electrical conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

First-principles study of quantum confinement and surface effects on the electronic properties of InAs nanowires

We have used first principles methods to systematically investigate the quantum confinement effect on the electronic properties of zinc-blende (ZB) and wurtzite (WZ) InAs nanowires (NWs) with different orientations and diameters, and compared their electronic properties before and after pseudo-hydrogen passivation. The results show that the calculated carrier effective masses are dependent on the NW diameter, except for [110] ZB NWs, and the hole effective masses of [111] ZB NWs are larger than the electron effective masses when the NW diameter is ≥26 Å. The band alignments of [111] ZB and [0001] WZ NWs reveal that the effect of quantum confinement on the conduction bands is greater than on the valence bands, and the position of the valence band maximum level changes little with increasing NW diameter. The pseudo-hydrogen passivated NWs have larger band gaps than the corresponding unpassivated NWs. The carrier effective masses and mobilities can be adjusted by passivating the surface dangling bonds.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Photoluminescence properties and energy levels of RE (RE = Pr, Sm, Er, Tm) in layered-CaZnOS oxysulfide

RE{sup 3+} (RE = Pr, Sm, Er, Tm)-activated CaZnOS samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. Doping with RE{sup 3+} (RE = Pr, Sm, Er, Tm) into layered-CaZnOS resulted in typical RE{sup 3+} (RE = Pr, Sm, Er, Tm) f-f line absorptions and emissions, as well as the charge transfer band of Sm{sup 3+} at about 3.3 eV. The energy level scheme containing the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions with respect to the valence and conduction bands of CaZnOS has been constructed based on the new data presented in this work, together with the data from literature on Ce{sup 3+} and Eu{sup 2+} doping in CaZnOS. The detailed energy level scheme provides a platform for interpreting the optical spectra and could be used to comment on the valence stability of the lanthanide ions in CaZnOS.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Structure and interface chemistry of MoO{sub 3} back contacts in Cu(In,Ga)Se{sub 2} thin film solar cells

Molybdenum oxide (MoO{sub 3}) is considered as a possible primary back contact for Cu(InGa)Se{sub 2} thin film solar cells for its potential as a transparent back contact for superstrate and bifacial devices. MoO{sub 3} films were deposited on Mo or ITO-coated soda lime glass substrates by reactive rf sputtering in an ambient of Ar + O{sub 2} with O{sub 2}/(O{sub 2} + Ar) = 35% on which Cu(In{sub 0.7}Ga{sub 0.3})Se{sub 2} alloy absorber layers were deposited using multi-source elemental evaporation. Scanning Electron Microscopy studies showed uniform coverage of the as-deposited MoO{sub 3} layer and good adhesion was obtained in all cases. X-ray Photoelectron Spectroscopy depth profile analysis showed that MoSe{sub 2} was not formed at the Cu(InGa)Se{sub 2} interface with either the Mo-MoO{sub 3} or ITO-MoO{sub 3} back contacts. Determination of the valence band offsets showed that the MoO{sub 3} layer at the interface changes the energy band alignment with Cu(InGa)Se{sub 2}, producing a primary contact with lower valence band offset than ITO. Cu(In,Ga)Se{sub 2} thin film solar cells prepared using an as-deposited Mo-MoO{sub 3} back contact yielded a best conversion efficiency of 14%, with V{sub OC} = 647 mV, J{sub SC} = 28.4 mA/cm{sup 2}, and FF = 78.1%. Cells with ITO-MoO{sub 3} back contact showed a best efficiency of 12%, with V{sub OC} = 642 mV, J{sub SC} = 26.8 mA/cm{sup 2}, and FF = 69.2%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗