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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on SrNd3Fe4(AsO)4 by Materials Project

SrNd3Fe4(AsO)4 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Sr2+ is bonded in a 4-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All Sr–As bond lengths are 3.46 Å. All Sr–O bond lengths are 2.46 Å. There are two inequivalent Nd3+ sites. In the first Nd3+ site, Nd3+ is bonded in a 4-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All Nd–As bond lengths are 3.54 Å. All Nd–O bond lengths are 2.30 Å. In the second Nd3+ site, Nd3+ is bonded in a 4-coordinate geometry to four As3- and four equivalent O2- atoms. All Nd–As bond lengths are 3.52 Å. All Nd–O bond lengths are 2.32 Å. Fe+2.25+ is bonded to four As3- atoms to form a mixture of corner and edge-sharing FeAs4 tetrahedra. There are two shorter (2.61 Å) and two longer (2.62 Å) Fe–As bond lengths. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent Nd3+ and four equivalent Fe+2.25+ atoms. In the second As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent Nd3+ and four equivalent Fe+2.25+ atoms. In the third As3- site, As3- is bonded in a 8-coordinate geometry to two equivalent Sr2+, two equivalent Nd3+, and four equivalent Fe+2.25+ atoms. O2- is bonded to one Sr2+ and three Nd3+ atoms to form a mixture of corner and edge-sharing OSrNd3 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaYFe2(AsO)2 by Materials Project

LaYFe2(AsO)2 crystallizes in the tetragonal P4mm space group. The structure is three-dimensional. La3+ is bonded in a 4-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All La–As bond lengths are 3.40 Å. All La–O bond lengths are 2.40 Å. Y3+ is bonded in a 4-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All Y–As bond lengths are 3.43 Å. All Y–O bond lengths are 2.29 Å. Fe2+ is bonded to four As3- atoms to form a mixture of corner and edge-sharing FeAs4 tetrahedra. All Fe–As bond lengths are 2.60 Å. There are two inequivalent As3- sites. In the first As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent La3+ and four equivalent Fe2+ atoms. In the second As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent Y3+ and four equivalent Fe2+ atoms. O2- is bonded to two equivalent La3+ and two equivalent Y3+ atoms to form a mixture of corner and edge-sharing OLa2Y2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La3YFe4(AsO)4 by Materials Project

La3YFe4(AsO)4 crystallizes in the orthorhombic Pmm2 space group. The structure is three-dimensional. there are two inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 4-coordinate geometry to four equivalent As3- and four O2- atoms. All La–As bond lengths are 3.40 Å. There are two shorter (2.38 Å) and two longer (2.41 Å) La–O bond lengths. In the second La3+ site, La3+ is bonded in a 4-coordinate geometry to four As3- and four O2- atoms. There are two shorter (3.40 Å) and two longer (3.43 Å) La–As bond lengths. There are three shorter (2.38 Å) and one longer (2.39 Å) La–O bond lengths. Y3+ is bonded in a 4-coordinate geometry to four equivalent As3- and four O2- atoms. All Y–As bond lengths are 3.46 Å. There are two shorter (2.25 Å) and two longer (2.28 Å) Y–O bond lengths. There are three inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to four As3- atoms to form a mixture of edge and corner-sharing FeAs4 tetrahedra. There are two shorter (2.62 Å) and two longer (2.63 Å) Fe–As bond lengths. In the second Fe2+ site, Fe2+ is bonded to four As3- atoms to form a mixture of edge and corner-sharing FeAs4 tetrahedra. There are two shorter (2.60 Å) and two longer (2.63 Å) Fe–As bond lengths. In the third Fe2+ site, Fe2+ is bonded to four As3- atoms to form a mixture of edge and corner-sharing FeAs4 tetrahedra. There are two shorter (2.62 Å) and two longer (2.63 Å) Fe–As bond lengths. There are three inequivalent As3- sites. In the first As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent La3+ and four Fe2+ atoms. In the second As3- site, As3- is bonded in a 8-coordinate geometry to four equivalent La3+ and four Fe2+ atoms. In the third As3- site, As3- is bonded in a 8-coordinate geometry to two equivalent La3+, two equivalent Y3+, and four Fe2+ atoms. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to three La3+ and one Y3+ atom to form OLa3Y tetrahedra that share corners with four equivalent OLa3Y tetrahedra and edges with four OLa2Y2 tetrahedra. In the second O2- site, O2- is bonded to two equivalent La3+ and two equivalent Y3+ atoms to form OLa2Y2 tetrahedra that share corners with four OLa2Y2 tetrahedra and edges with four equivalent OLa3Y tetrahedra. In the third O2- site, O2- is bonded to four La3+ atoms to form OLa4 tetrahedra that share corners with four OLa2Y2 tetrahedra and edges with four equivalent OLa3Y tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Geometrical frustration versus Kitaev interactions in BaCo 2 (AsO 4 ) 2

Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid (KSL) state. One of the front-runners is BaCo 2 (AsO 4 ) 2 (BCAO), where it was suggested that the exchange processes between Co 2+ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze a comprehensive inelastic neutron scattering (INS) study of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelastic spin structure factor measured in zero magnetic field, we examine two leading theoretical models: the Kitaev-type JK Γ Γ ′ model and the XXZ - J 1 - J 3 model. We show that the existing experimental data can be consistently accounted for by the XXZ - J 1 - J 3 model but not by the JK Γ Γ ′ model, and we discuss the implications of these results for the realization of a spin liquid phase in BCAO and more generally for the realization of the Kitaev model in cobaltates.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Scaling behavior and giant field enhancement of the thermal conductivity in the honeycomb antiferromagnet BaCo 2⁢ (AsO 4 ) 2

The layered honeycomb material BaCo 2 (AsO 4 ) 2 is of topical interest because its magnetic state is related to that of the Kitaev magnet α-RuCl 3 . Using thermal transport to probe how magnetic excitations interact with phonons in the magnetically disordered regime, we have uncovered an unusually large enhancement of the thermal conductivity κ xx in an in-plane magnetic field H. Just above the Néel temperature T N , a field of 13 T increases κ xx by a factor of ∼ 211, which is very large compared to other magnetic insulators. Interestingly, κ xx (H, T) exhibits a scaling behavior in the entire magnetically disordered region that surrounds the ordered zigzag state. The ratio Δκ xx (H, T)/κ xx (13, T), measured throughout the disordered region, collapses to a one-parameter scaling function exp(−1/gx) (where x = μ B B/k B T and g is a constant).

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structural Assessment of Fluorine, Chlorine, Bromine, Iodine, and Hydroxide Substitutions in Lead Arsenate Apatites (Mimetites)–Pb 5 (AsO 4 ) 3 X

Five lead-arsenate apatites (mimetites)-Pb 5 (AsO 4 ) 3 X—where X denotes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and hydroxide (OH)—were synthesized via precipitation from aqueous solutions. The crystal structures were determined through Rietveld refinement of powder synchrotron X-ray data. All the compounds crystallized in the hexagonal class symmetry (space group P6 3 /m). The Rietveld refinement indicated that mimetite-Cl, -Br, -I, and -OH had an anion deficiency at position X. Substitution of halogens in a mimetite structure brought about systematic changes in unit-cell parameters, interatomic distances, and metaprism twist angles φ, proportional to the substituted halogen’s ionic radius. Mimetite-OH did not follow the linear correlations determined within the series. Twist angle φ, a useful device for monitoring changes in apatite topology, ranged from 20.34° for mimetite-F to 11.42° for mimetite-I. The geometric method has been proposed for determining the diameter of hexagonal channels hosting halogens in apatites. A comparison of the results with halogenated pyromorphites showed similar systematic trends: the substitutions in mimetites have comparable effect on the interatomic distances as in their phosphorous analogues.

58 GEOSCIENCES↗
NASA NTRS1989

Coordination of Advanced Solar Observatory (ASO) Science Working Group (SWG) for the study of instrument accommodation and operational requirements on space station

The objectives are to coordinate the activities of the Science Working Group (SWG) of the Advanced Solar Observatory (ASO) for the study of instruments accommodation and operation requirements on board space station. In order to facilitate the progress of the objective, two conferences were organized, together with two small group discussions.

Wu, S. T.↗
DOE OSTI2020

Materials Data on Ba2MnZn2(AsO)2 by Materials Project

Ba2MnZn2As2O2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ba2+ is bonded in a 8-coordinate geometry to four equivalent As3- and four equivalent O2- atoms. All Ba–As bond lengths are 3.46 Å. All Ba–O bond lengths are 2.79 Å. Mn2+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Mn–O bond lengths are 2.14 Å. Zn2+ is bonded to four equivalent As3- atoms to form a mixture of edge and corner-sharing ZnAs4 tetrahedra. All Zn–As bond lengths are 2.61 Å. As3- is bonded in a 4-coordinate geometry to four equivalent Ba2+ and four equivalent Zn2+ atoms. O2- is bonded to four equivalent Ba2+ and two equivalent Mn2+ atoms to form a mixture of edge, face, and corner-sharing OBa4Mn2 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrNd7Fe8(AsO)8 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr2MnZn2(AsO)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
NASA NTRS1989

Advanced Solar Observatory (ASO) accommodations requirements study

Results of an accommodations analysis for the Advanced Solar Observatory on Space Station Freedom are reported. Concepts for the High Resolution Telescope Cluster, Pinhole/Occulter Facility, and High Energy Cluster were developed which can be accommodated on Space Station Freedom. It is shown that workable accommodations concepts are possible. Areas of emphasis for the next stage of engineering development are identified.

Source record↗
DOE OSTI2020

Iron(III)–Oxo Cluster Chemistry with Dimethylarsinate Ligands: Structures, Magnetic Properties, and Computational Studies

A program has been initiated to develop Fe III /oxo cluster chemistry with the ‘pseudo-carboxylate’ ligand dimethylarsinate (Me 2 AsO 2 - ) for comparison with the well investigated Fe III /oxo/carboxylate cluster area. The synthesis and characterization of three polynuclear Fe III complexes are reported, [Fe 12 O 4 (O 2 C t Bu) 8 (O 2 AsMe 2 ) 17 (H 2 O) 3 ]Cl 3 (1), Na 2 [Fe 12 Na 2 O 4 (O 2 AsMe 2 ) 20 (NO 3 ) 6 (Me 2 AsO 2 H) 2 (H 2 O) 4 ](NO 3 ) 6 (2) and [Fe 3 (O 2 AsMe 2 ) 6 (Me 2 AsO 2 H) 2 (hqn) 2 ](NO 3 ) (3), where hqn is 8-hydroxyquinoline. The Fe 12 core of 1 is a type never previously encountered in Fe III carboxylate chemistry, consisting of two Fe 6 units each of which comprises two {Fe 3 (μ 3 -O 2- )} units bridged by three Me 2 AsO 2 - groups and linked into an Fe 12 loop structure by two anti-anti η 1 :η 1 :μ Me 2 AsO 2 - groups, a bridging mode extremely rare with carboxylates. 2 also consists of two Fe 6 units, differing in their ligation from those in 1, and this time linked together into a linear structure by a central {Na 2 (NO 3 ) 2 } bridging unit. 3 is a linear Fe 3 complex with no monoatomic bridges between Fe III ions, a very rare situation in Fe III chemistry with any ligands, and unprecedented in Fe carboxylate chemistry. The distinct differences observed in arsinate vs carboxylate ligation modes are rationalized largely based on the greater basicity of the former vs the latter. Variable-temperature dc and ac magnetic susceptibility data reveal all Fe 2 pairwise interactions to be antiferromagnetic. For 1 and 2, the different J ij couplings were estimated by use of a magnetostructural correlation for high nuclearity Fe III -oxo clusters and by density functional theory calculations using broken symmetry methods, allowing identification of their relative spin vector alignments and thus rationalization of their S = 0 ground states. The J ij values were then used as input values to give excellent fits of the experimental χM T vs T data. For 3, the fits of the experimental χM T vs T data to the Van Vleck equation or with PHI gave a very weak J 12 = -0.8(1) cm -1 (H = –2JŠ i ·Š j convention) between adjacent Fe III ions, and an S = 5/2 ground state. Furthermore, these initial Fe III arsinate complexes also provide structural parameters that help validate literature assignments of arsinate binding modes to iron oxide/hydroxide minerals as part of environmental concerns of using arsenic-containing herbicides in agriculture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

The Advanced Solar Observatory

A conceptual plan for the development of a comprehensive long duration solar space observatory, The Advanced Solar Observatory (ASO) is described. The ASO is intended to provide solar astronomers with the observational power necessary to address fundamental problems relating to the solar convection zone and activity cycle; the thermal and nonthermal processes that control the transport of energy, mass, and magnetic flux in the solar atmosphere; the generation of the solar wind; and the dynamics of the inner heliosphere. The ASO concept encompasses three proposed Space Station-based instrument ensembles: (1) the High Resolution Telescope Cluster, which includes far ultraviolet, extreme ultraviolet, and X-ray telescopes; (2) the Pinhole/Occulter Facility, which includes Fourier transform and coded aperture hard X-ray and gamma ray telescopes and occulted ultraviolet and visible light coronagraphs; and (3) the High Energy Facility, which contains neutron, gamma ray, and low frequency radio spectrometers. Two other facilities, the Orbiting Solar Laboratory, and a package of Global Dynamics Instrumentation, will, with the Space Station ensembles, form a comprehensive capability for solar physics. The scientific program of the ASO, current instrument concepts for the Space Station based ASO instrument ensembles, and plans for their accommodation on the Space Station are described.

Walker, Arthur B. C., Jr.↗