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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study

The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe3+ sites, that are alternately corner-shared [FeO5]7 square pyramids and [FeO6]9 octahedra, forming into [Fe4O18]24 rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of shortrange magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and hightemperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, 1/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe3+ are only of the order 3.0 B, smaller than the expected values near 4.5 B, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic structure.

Thompson, Corey↗
DOE OSTI2019

A neutron diffraction demonstration of long-range magnetic order in the quasicrystal approximant DyCd 6

We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd 6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Néel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic Im 3¯ structure using a combination of two propagation vectors, k 1 = [0 0 0] and k 2 = [1/2 0 1/2], yielding ‘anti-I’ order. Furthermore, when referred to the monoclinic C 2/ c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0].

36 MATERIALS SCIENCE↗
DOE OSTI2017

Path length dependent neutron diffraction peak shifts observed during residual strain measurements in U–8 wt% Mo castings

This study reports an angular diffraction peak shift that scales linearly with the neutron beam path length traveled through a diffracting sample. This shift was observed in the context of mapping the residual stress state of a large U–8 wt% Mo casting, as well as during complementary measurements on a smaller casting of the same material. If uncorrected, this peak shift implies a non-physical level of residual stress. A hypothesis for the origin of this shift is presented, based upon non-ideal focusing of the neutron monochromator in combination with changes to the wavelength distribution reaching the detector due to factors such as attenuation. The magnitude of the shift is observed to vary linearly with the width of the diffraction peak reaching the detector. Consideration of this shift will be important for strain measurements requiring long path lengths through samples with significant attenuation. This effect can probably be reduced by selecting smaller voxel slit widths.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural Evolution and Transition Dynamics in Lithium Ion Battery under Fast Charging: An Operando Neutron Diffraction Investigation

Abstract Fast charging (<15 min) of lithium‐ion batteries (LIBs) for electrical vehicles (EVs) is widely seen as the key factor that will greatly stimulate the EV markets, and its realization is mainly hindered by the sluggish diffusion of Li + . To have a mechanistic understanding of Li + diffusion within LIBs, in this study, structural evolutions of electrodes for a Ni‐rich LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) || graphite cylindrical cell with high areal loading (2.78 mAh cm −2 ) are developed for operando neutron powder diffraction study at different charging rates. Via sequential Rietveld refinements, changes in structures of NMC622 and Li x C 6 are obtained during moderate and fast charging (from 0.27 C to 4.4 C). NMC622 exhibits the same structural evolution regardless of C‐rates. For phase transitions of Li x C 6 , the stage I (LiC 6 ) phase emerges earlier during the stepwise intercalation at a lower state of charge when charging rate is increased. It is also found that the stage II (LiC 12 ) → stage I (LiC 6 ) transition is the rate‐limiting step during fast charging. The LiC 12 → LiC 6 transition mechanism is further analyzed using the Johnson–Mehl–Avrami–Kolmogorov model. It is concluded as a diffusion‐controlled, 1D phase transition with decreasing nucleation kinetics under increasing chargingrates.

25 ENERGY STORAGE↗
DOE OSTI2012

Neutron diffraction and magnetic study of the low-temperature transitions in SrMo{sub 1−x}Fe{sub x}O{sub 3−δ}

Highlights: ► SrMo{sub 1−x}Fe{sub x}O{sub 3−δ} (x = 0, 0.1, 0.2 and 0.3) were obtained as polycrystalline powders. ► Cooling, two structural transitions are identified, tetragonal and orthorhombic. ► DSC curves exhibit an endothermic peak close to 240 K. ► Magnetic behavior of the samples changes, inducing a ferromagnetic character. ► The tilt angles are appreciably high at low temperatures. -- Abstract: SrMo{sub 1−x}Fe{sub x}O{sub 3−δ} (x = 0, 0.1, 0.2 and 0.3) perovskites have recently been described as performing anode materials in solid-oxide fuel cells. In this work, we describe the structural phase transitions they undergo below room-temperature (RT), studied “in-situ” from neutron powder diffraction data and DSC measurements. At RT all the studied compositions are cubic, space group Pm-3m, with unit-cell parameters that decrease with Fe doping. Upon cooling the samples, two structural phase transitions are identified: one to a tetragonal structure with I4/mcm space group (around T{sub 1} = 240 K), and the second one to an orthorhombic Imma phase below T{sub 2} = 100 K. The magnetic properties have also been evaluated; the Fe substitution drives an evolution from a Pauli-paramagnetic state (x = 0) to a weak ferromagnetic state combined with antiferromagnetic interactions; the susceptibility and the saturation magnetization increases monotonically with increasing the Fe-doping content.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Heat capacity and neutron diffraction studies on the frustrated magnetic Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [0{<=}x{<=}1] solid solution

The Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [0{<=}x{<=}1] solid solution exhibits a complex magnetic behaviour due to the bond-frustration in its magnetic structure. Heat capacity measurements of the (x=0.1-0.5) phases show a three-dimensional magnetic ordering ({lambda} anomaly) that shifts to lower temperatures and becomes broader as the AsO{sub 4}{sup 3-} content increases. For x=0.75, no significant feature was observed whereas for higher arsenate ion content, x=0.9 and 1, a small maximum was detected. The magnetic structures of solid solution are consistent with the existence of predominant antiferromagnetic superexchange interactions through the |OH| and |XO{sub 4}| (X=P and As) groups between the Co{sup +2} ions. The substitution of PO{sub 4}{sup 3-} by AsO{sub 4}{sup 3-} anions by more than 90% substantially modifies the magnetic exchange pathways in the solid solution, leading to an incommensurate antiferromagnetic structure in Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [x=0.9 and 1] phases. - Graphical abstract: Magnetic structures of Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} [0{<=}x{<=}1]. The ordering of the magnetic moments of Co{sup 2+} is in c direction for the two crystallographic positions (dimers and chains) in all compounds. The unit cell is surrounded by a red line. Highlights: Black-Right-Pointing-Pointer Synthesis of a new adamite-type compounds, Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} (0.1, 0.25, 0.5, 0.75, 0.9) phases. Black-Right-Pointing-Pointer Co{sub 2}(OH)(PO{sub 4}){sub 1-x}(AsO{sub 4}){sub x} (0-1) solid solution; magnetic frustrated system. Black-Right-Pointing-Pointer High resolution neutron powder diffraction to determine the crystal structures. Black-Right-Pointing-Pointer Incommensurate magnetic structures at low temperature. Black-Right-Pointing-Pointer Magnetostructural correlations in cobalt-based Co{sub 2}(OH)XO{sub 4} (X=P and As) insulation compounds.

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

A Multi-Anode Photomultiplier Tube Based Wavelength-Shifting-Fiber Detector for neutron diffraction

The wavelength-shifting (WLS) fiber scintillator neutron detectors were developed for two time-of-flight (TOF) neutron powder diffractometers (POWGEN, VULCAN) at Spallation Neutron Source (SNS). In a recent module (v3.0), however, there are 32 1-inch-diameter photomultiplier tubes (PMTs) which are bulky and expensive. We built a new detector module (v3.1) based on four multi-anode (MA) PMTs, and tested its performance including detection efficiency, count rate capability, spatial resolution, ghosting properties, and gamma-ray sensitivity. The v3.1 module was compared with two prior v3.0 modules, and 3He tube detectors.

Berry, Kevin D↗
DOE OSTI2018

Metastable Li 1+δ Mn 2 O 4 (0 ≤ δ ≤ 1) Spinel Phases Revealed by in Operando Neutron Diffraction and First-Principles Calculations

Here, we examine the reaction mechanisms driven by the lithiation of Li 1+δ Mn 2 O 4 (0 ≤ δ ≤ 1) spinels via in operando neutron powder diffraction (NPD). New reaction mechanisms are proposed involving solid-solution regions within both cubic and tetragonal spinel phases in addition to a continuous phase transition between them. In operando NPD is an ideal tool to follow the light elements such as lithium and oxygen in cathode materials which are often the key to fully understand their structural evolutions. Here, we report a novel methodology to prepare an extremely thick electrode with ~378 mg·cm –2 loading density suitable for the in operando NPD studies. Enabled by such thick electrode, we find that the metal oxygen M–O (M = Li and Mn) bond lengths in both end members LiMn 2 O 4 and Li 2 Mn 2 O 4 experience pronounced changes larger than dictated by the change in lattice parameters because of the locally formed Jahn–Teller distorted Mn 3+ . First-principles density functional theory calculations confirm these metastable intermediates and further propose atomistic reaction pathways for the phase transition by coupling a global structure search algorithm. In conclusion, these findings redefine the conventional understandings on two-phase reactions of this spinel material.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Long-range three-dimensional magnetic structures of the spin S =1 hexamer cluster fedotovite-like A 2 Cu 3 O ( SO 4 ) 3 ( A 2 = K 2 , NaK, Na 2 ): A neutron diffraction study

The crystal and magnetic structures of the spin S = 1 hexamer cluster fedotovite-like A 2 Cu 3 O(SO 4 ) 3 (A 2 = K 2 , NaK, Na 2 ) were studied by neutron powder diffraction at temperatures 1.6–290 K. The crystal structures in all compounds are well refined in the monoclinic space group C2/c. The basic magnetic units of the compounds are copper hexamers, which are coupled by weak superexchange interactions giving rise to three-dimensional long-range magnetic order below 3.0 < T N < 4.7 K. We have found that for A 2 = K 2 and NaK the propagation vector of the magnetic structure is k = [0,0,0], and the coupling of the Cu hexamers is ferromagnetic (FM) along the ab diagonal and antiferromagnetic along the bc diagonal. In contrast, for A = Na the propagation vector is k = [0,1,0], and the Cu hexamers are coupled antiferromagnetically (AFM) along the ab diagonal. Further, the hexamers are formed by three Cu pairs arranged along the b axis. The calculated spin expectation values $\langle s \rangle$ for the simplest symmetric spin Hamiltonian (obtained from inelastic neutron spectroscopy) of the isolated hexamers in the mean field amounted to $\langle s \rangle$ = 3/8 for the side spins Cu1 and Cu2 and $\langle s \rangle$ = 1/4 for Cu3 in the middle. The Cu spins are FM coupled in pairs and AFM between neighboring pairs. The experimental magnetic moments of the Cu 2+ ions turn out to be not completely collinear due to spin frustrations within the weak interhexamer interactions. The sizes of magnetic moments of Cu in the hexamers determined from the diffraction data are in fair agreement with the calculated values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Asymmetric band flipping for time-of-flight neutron diffraction data

Charge flipping with powder diffraction data is known to produce a result more reliably with high-resolution data, i.e. visible reflections at small d spacings. This data are readily accessible with the neutron time-of-flight technique but the assumption that negative scattering density is nonphysical is no longer valid where elements with negative scattering lengths are present. The concept of band flipping was introduced in the literature, where a negative threshold is used in addition to a positive threshold during the flipping. But, it was not tested with experimental data at the time. Finallly, band flipping has been implemented in TOPAS together with the band modification of low-density elimination and tested with experimental powder and Laue single-crystal neutron data.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Preparation and structural study from neutron diffraction data of Pr{sub 5}Mo{sub 3}O{sub 16}

The title compound has been prepared as polycrystalline powder by thermal treatments of mixtures of Pr{sub 6}O{sub 11} and MoO{sub 2} in air. In the literature, an oxide with a composition Pr{sub 2}MoO{sub 6} has been formerly described to present interesting catalytic properties, but its true stoichiometry and crystal structure are reported here for the first time. It is cubic, isostructural with CdTm{sub 4}Mo{sub 3}O{sub 16} (space group Pn-3n, Z=8), with a=11.0897(1) A. The structure contains MoO{sub 4} tetrahedral units, with Mo-O distances of 1.788(2) A, fully long-range ordered with PrO{sub 8} polyhedra; in fact it can be considered as a superstructure of fluorite (M{sub 8}O{sub 16}), containing 32 MO{sub 2} fluorite formulae per unit cell, with a lattice parameter related to that of cubic fluorite (a{sub f}=5.5 A) as a{approx}2a{sub f}. A bond valence study indicates that Mo exhibits a mixed oxidation state between 5+ and 6+ (perhaps accounting for the excellent catalytic properties). One kind of Pr atoms is trivalent whereas the second presents a mixed Pr{sup 3+}-Pr{sup 4+} oxidation state. The similarity of the XRD pattern with that published for Ce{sub 2}MoO{sub 6} suggests that this compound also belongs to the same structural type, with an actual stoichiometry Ce{sub 5}Mo{sub 3}O{sub 16}. -- Graphical Abstract: Formerly formulated as Pr{sub 2}MoO{sub 6}, the title compound is a cubic superstructure of fluorite (a=11.0897(1) A, space group Pn-3n) due to the long-range ordering of PrO{sub 8} scalenohedra and MoO{sub 4} tetrahedral units, showing noticeable shifts of the oxygen positions in order to provide a tetrahedral coordination for Mo ions. A mixed valence Mo{sup 5+}-Mo{sup 6+} is identified, which could account for the excellent catalytic properties of this material. Display Omitted

36 MATERIALS SCIENCE↗
DOE OSTI2012

Isotope effects in water as investigated by neutron diffraction and path integral molecular dynamics

The structure of heavy and light water at 300 K was investigated by using a joint approach in which the method of neutron di raction with oxygen isotope substitution was combined with path integral molecular dynamics simulations. The di raction results, which give intra-molecular O-D and O-H bond distances of 0.985(5) and 0.990(5) A, were found to be in best agreement with those obtained by using the exible anharmonic TTM3-F water model. Both techniques show a di erence of '0.5% between the O-D and O-H intra-molecular bond lengths and the results support a competing quantum e ects model for water in which its structural and dynamical properties are governed by an o set between intra-molecular and inter-molecular quantum contributions. Further consideration of the O-O correlations is needed in order to improve agreement with experiment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗