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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Vibration and buckling of general periodic lattice structures

A method is presented for vibration and buckling analysis of arbitrary lattice structures having repetitive geometry in any combination of coordinate directions. The approach is based on exact member theory for representing the stiffness of an individual member subject to axial load, and in the case of vibration, undergoing harmonic oscillation. The method is an extension of previous work that was limited to specific geometries. The resulting eigenvalue problem is of the size associated with the repeating element of the structure. A computer program has been developed incorporating the theory and results are given for vibration of rectangular platforms and a large antenna structure having rotational symmetry. Buckling and vibration results for cable-stiffened rings are also given.

Anderson, M. S.↗
NASA NTRS2011

Molybdenum Valence in Basaltic Silicate Melts: Effects of Temperature and Pressure

The metal-silicate partitioning behavior of molybdenum has been used as a test for equilibrium core formation hypotheses [for example, 1-6]. However, current models that apply experimental data to equilibrium core-mantle differentiation infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Molybdenum, a multi-valent element with a valence transition near the fO2 of interest for core formation (approx.IW-2) will be sensitive to changes in fO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo(6+) can be either octahedrally or tetrahedrally coordinated. Here we present X-ray absorption near edge structure (XANES) measurements of Mo valence in basaltic run products at a range of P, T, and fO2 and further quantify the valence transition of Mo.

Danielson, L. R.↗
DOE OSTI2023

Elucidating the speciation of extracted lanthanides by diglycolamides

Many studies over the past few decades have been devoted to addressing the application of diglycolamides (DGAs) for hydrometallurgical-based, f-element separations. Work to date has shown the molecular structure of a DGA derivative can have a significant impact on intra-lanthanide partitioning patterns. More recent studies have pushed towards probing the structure function relationship of the lanthanide-DGA complex to enable the design of more efficient lanthanide separation systems. Spectroscopic techniques, such as UV–Visible, Fourier Transformed Infrared Spectroscopy (FT-IR), Nuclear Magnetic Resonance (NMR), and Extended X-ray Absorption Fine Structure (EXAFS), provide information regarding the inner-sphere coordination of a given lanthanide-DGA complex. Scattering techniques, such as Dynamic Light Scattering (DLS), Small-Angle X-ray Scattering (SAXS), and Small-Angle Neutron Scattering (SANS), address nanoscale structures including aggregate sizes and morphology. Here, this review assesses the current state-of-knowledge regarding lanthanide-DGA hydrometallurgical (i.e., solvent extraction systems) interrogated using spectroscopic and scattering techniques to characterize the extracted Ln 3+ DGA species. Of particular interest to this review is the impact of varied diluents, inclusion and variation of phase modifiers, and DGA derivatization on system characteristics. While there has been extensive literature on the application of DGAs for f-element separations, the literature lacks a collective assessment of the speciation of Ln 3+ in the organic phase. This review provides new insights into the field of DGA separations, explicitly with an application to intra-lanthanide separations. Specifically, this review illustrates the importance of both the co-extraction anion (Cl - , NO 3 - , or ClO 4 - ) as it pertains to both the aggregate size and Ln 3+ distribution coefficient. It is evident the ability of the anion to disrupt the hydrogen bonding network limits both aggregate size and distribution coefficients according to the Hoffmeister series. This suggests the importance of the large, softer anions with a low charge-to-surface area ratio on encouraging hydrogen bond interactions. In addition, the co-extracted cation (H + vs Na + ) is important for mitigating transfer of Ln 3+ from the aqueous to the organic phase through extensive hydrogen bonding networks. These networks are responsible for forming supramolecular aggregates where a change in morphology is observed with increasing concentrations of H + and/or Ln 3+ in the organic phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2005

Spectral Diversity at Gusev Crater from Coordinated Mini-TES and Pancam Observations

During the last year the Spirit rover has explored Gusev crater with the Athena payload. Two remote sensing instruments collected spectral information at visible (Pancam) and at thermal infrared Mini-TES) wavelengths. Observations for these instruments were coordinated and targeted to determine the mineralogical diversity and identify specific lithologies / end members for detailed investigations with the rest of the payload. Initial results were reported last spring. A wide range of materials have been measured including outcrops, rocks, and soils. Both natural and brushed/ratted rocks and natural and disturbed soils have also been measured permitting investigations of coating and soil structure. As of Jan 9, 2005, over 400 coordinated observations have been made.

Blaney, D. L.↗
DOE OSTI2020

Morphing Mn core @Pt shell nanoparticles: Effects of core structure on the ORR performance of Pt shell

Currently, the catalysts performance for the oxygen reduction reaction (ORR) is limited by two major factors, their price and the scaling relationship, i.e. constant offset, between the binding energy of reactants and reaction intermediates. Here we show that both limitations may be eased by using nanoparticle catalysts composed of a core of earth-abundant Mn and Pt shell of two atomic layers. We report the unusual atomic-structure of Mn core renders the distribution of coordination numbers and related atomic-level stresses on the Pt shell very broad in com- parison to pure Pt particles. This increases the chances of nearby sites on the shell to affect each other’s activity such that the dissociative absorption of molecular oxygen is facilitated without correspondingly increasing the binding strength of reaction intermediates, thereby promoting the ORR kinetics. Our findings introduce the concept of structural flexibility of the 3d-metal core and 5d-Pt shell as a strategy for catalysis performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ab initio molecular dynamics simulation of Nd3+ incorporation in calcite

Trivalent rare-earth elements (REEs) readily incorporate in Ca-bearing minerals such as calcite (CaCO3), a phenomenon with important implications for the use of REEs as biogeochemical tracers as well as for environmental remediation. Despite substantial efforts, determining the incorporation modes of trivalent REEs in calcite has remained challenging due to their presence in multiple coordination environments. This is particularly problematic for the interpretation of extended X-ray absorption fine structure (EXAFS) spectroscopy. In this work, ab initio molecular dynamics (AIMD) simulations of Nd3+ incorporated in calcite were performed to resolve its incorporation modes. Nd3+ and Ca2+ have very similar ionic radii but the additional positive charge requires a charge compensation scheme (CCS). Five CCSs were considered in AIMD simulations, and the resulting atomic trajectories were then used to compute EXAFS spectra for direct fitting to a published experimental spectrum. The results of the fits indicated that Nd3+ incorporates at the Ca2+ site in calcite in a mixture of six- and seven-fold coordination environments and through three main incorporation modes: associated with a protonated nearest-neighbor Ca2+ vacancy, incorporated as NdOH2+, and charge compensated by a remote species (on the spatial scale probed by EXAFS). The incorporation of Nd3+ in calcite via multiple modes was consistent with previous work, but the AIMD-EXAFS approach allowed for resolving the nature, proportion, and structure of the different coordination environments.

Kerisit, Sebastien N.↗
DOE OSTI2026

Transition from Vehicular to Structural Ionic Transport in Electrified Alkali Aqueous Solutions

A molecular understanding of the solvation and dynamics of ions under static electric fields is crucial for modelling a wide range of natural and technological processes. Yet, traditional simulation methods suffer from a trade-off that has to be made between accuracy and statistical convergence. To bridge this gap, herein we extend our recently introduced Perturbed Neural Network Potential Molecular Dynamics (PNNP MD) approach to investigate the solvation structures and ionic transport mechanisms of electrified alkali cationic solutions. We obtain ionic conductivities for Li+, Na+ and Cs+ from the field dependence of the ionic current density in good agreement with experiment. Surprisingly, the migration mechanism is found to be strikingly different for the three ions despite their similar ionic conductivities. While Li+ conducts predominantly through vehicular migration of a stable 4-fold coordinated ion at all field strengths, Cs+ conducts strictly through a structural diffusion mechanism, where 9-12 transient first shell water coordination bonds are broken and renewed. Notably, aqueous Na+ emerges as a “Goldilocks” ion: its ion-water interactions are strong enough to maintain distinct 5-6 fold coordination shells at zero field (unlike Cs+) yet labile enough to be strongly perturbed by electric fields (unlike Li+). As a consequence, we observe an electric field-induced transition from vehicular to structural ionic transport for Na+ that is accompanied by a marked increase in the ionic current density. Our results imply that the conductance mechanism of ions with moderate ion-solvent interactions can be effectively tuned by external electric fields.

Joll, Kit↗
DOE OSTI2020

Materials Data on GaTe4(MoSe)4 by Materials Project

GaMo4Se4Te4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo+3.25+ is bonded in a 3-coordinate geometry to three equivalent Te2- and three equivalent Se2- atoms. All Mo–Te bond lengths are 2.94 Å. All Mo–Se bond lengths are 2.50 Å. Ga3+ is bonded in a tetrahedral geometry to four equivalent Te2- atoms. All Ga–Te bond lengths are 2.58 Å. Te2- is bonded in a 1-coordinate geometry to three equivalent Mo+3.25+ and one Ga3+ atom. Se2- is bonded in a 12-coordinate geometry to three equivalent Mo+3.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GaSi(MoS2)4 by Materials Project

GaSi(MoS2)4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo+2.25+ is bonded in a 6-coordinate geometry to six S2- atoms. There are three shorter (2.36 Å) and three longer (2.93 Å) Mo–S bond lengths. Ga3+ is bonded to four equivalent S2- atoms to form GaS4 tetrahedra that share corners with four equivalent SiS4 tetrahedra. All Ga–S bond lengths are 2.50 Å. Si4+ is bonded to four equivalent S2- atoms to form SiS4 tetrahedra that share corners with four equivalent GaS4 tetrahedra. All Si–S bond lengths are 2.09 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted linear geometry to three equivalent Mo+2.25+, one Ga3+, and one Si4+ atom. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo+2.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on F2 by Materials Project

F2 crystallizes in the cubic Pm-3n space group. The structure is zero-dimensional and consists of eight hydrofluoric acid molecules. F is bonded in a 1-coordinate geometry to atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb3Pt4 by Materials Project

Yb3Pt4 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Yb+2.67+ is bonded in a 9-coordinate geometry to nine Pt2- atoms. There are a spread of Yb–Pt bond distances ranging from 2.83–3.20 Å. There are three inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded in a distorted octahedral geometry to six equivalent Yb+2.67+ atoms. In the second Pt2- site, Pt2- is bonded in a 7-coordinate geometry to seven equivalent Yb+2.67+ and three equivalent Pt2- atoms. There are one shorter (2.86 Å) and two longer (2.94 Å) Pt–Pt bond lengths. In the third Pt2- site, Pt2- is bonded in a 6-coordinate geometry to six equivalent Yb+2.67+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on I by Materials Project

I is Tungsten structured and crystallizes in the cubic Im-3m space group. The structure is zero-dimensional and consists of two hydriodic acid molecules. I is bonded in a 8-coordinate geometry to atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La4S7 by Materials Project

La4S7 crystallizes in the tetragonal I-42m space group. The structure is three-dimensional. La+2.50+ is bonded in a 8-coordinate geometry to eight S+1.43- atoms. There are four shorter (2.96 Å) and four longer (2.99 Å) La–S bond lengths. There are three inequivalent S+1.43- sites. In the first S+1.43- site, S+1.43- is bonded to five equivalent La+2.50+ atoms to form a mixture of distorted corner and edge-sharing SLa5 trigonal bipyramids. In the second S+1.43- site, S+1.43- is bonded in a 6-coordinate geometry to four equivalent La+2.50+ atoms. In the third S+1.43- site, S+1.43- is bonded in a 8-coordinate geometry to four equivalent La+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La2Os2I by Materials Project

La2Os2I crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. La+2.50+ is bonded in a 9-coordinate geometry to six equivalent Os2- and three equivalent I1- atoms. There are three shorter (3.12 Å) and three longer (3.25 Å) La–Os bond lengths. All La–I bond lengths are 3.58 Å. Os2- is bonded in a 9-coordinate geometry to six equivalent La+2.50+ and three equivalent Os2- atoms. All Os–Os bond lengths are 2.52 Å. I1- is bonded in a 6-coordinate geometry to six equivalent La+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nd4S7 by Materials Project

Nd4S7 crystallizes in the tetragonal P-42m space group. The structure is three-dimensional. Nd+2.50+ is bonded in a 8-coordinate geometry to eight S+1.43- atoms. There are a spread of Nd–S bond distances ranging from 2.90–2.96 Å. There are three inequivalent S+1.43- sites. In the first S+1.43- site, S+1.43- is bonded in a 8-coordinate geometry to four equivalent Nd+2.50+ atoms. In the second S+1.43- site, S+1.43- is bonded to five equivalent Nd+2.50+ atoms to form a mixture of distorted corner and edge-sharing SNd5 trigonal bipyramids. In the third S+1.43- site, S+1.43- is bonded in a 6-coordinate geometry to four equivalent Nd+2.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on GaGe(MoS2)4 by Materials Project

GaGe(MoS2)4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo+2.25+ is bonded in a 3-coordinate geometry to six S2- atoms. There are three shorter (2.36 Å) and three longer (3.01 Å) Mo–S bond lengths. Ga3+ is bonded to four equivalent S2- atoms to form GaS4 tetrahedra that share corners with four equivalent GeS4 tetrahedra. All Ga–S bond lengths are 2.34 Å. Ge4+ is bonded to four equivalent S2- atoms to form GeS4 tetrahedra that share corners with four equivalent GaS4 tetrahedra. All Ge–S bond lengths are 2.26 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted linear geometry to three equivalent Mo+2.25+, one Ga3+, and one Ge4+ atom. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo+2.25+ atoms.

36 MATERIALS SCIENCE↗