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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Structural distortion and incommensurate noncollinear magnetism in EuAg 4 As 2

Layered pnictide materials have provided a fruitful platform to study various emergent phenomena, including superconductivity, magnetism, charge density waves, etc. In this work, we report the observation of structural distortion and noncollinear magnetism in layered pnictide EuAg 4 As 2 via transport, magnetization, single crystal x-ray, and neutron diffraction data.EuAg 4 As 2 single crystal shows a structural distortion at 120 K, where two sets of superlattice peaks with the propagation vectors of q 1 =±(0, 0.25, 0.5) and q 2 =±(0.25, 0, 1) emerge. Between 9–15 K, the hexagonal Eu 2+ sublattice enters an unpinned incommensurate magnetic state, with magnetic Bragg reflections pictured as circular sectors. Furthermore, below 9 K, it orders in an incommensurate noncollinear antiferromagnetic state with a well-defined propagation wavevector of (0, 0.1, 0.12) and a very rare magnetic structure, which is helical along the c axis and cycloidal along the b axis with a moment of 6.4 μB/Eu 2+ . Furthermore, rich magnetic phases under magnetic fields, large magnetoresistance, and strong coupling between charge carriers and magnetism in EuAg 4 As 2 are revealed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Giant Doping Response of Magnetic Anisotropy in MnTe

Developing simple ways to control spin states in spintronic devices is a crucial step towards increasing their functionality. MnTe is a room-temperature antiferromagnet with promising spintronic properties, including for thermospintronics and magnon-based devices. Here, we show that, in MnTe, less than 1% Li is sufficient to produce a dramatic spin reorientation as observed by neutron diffraction. The behavior of the 0001 magnetic Bragg peak reveals a significant reorientation of the Mn spins from planar in the pure material to almost completely axial with minimal Li doping. Temperature dependence of the magnetic peaks in Li-doped samples indicates that axial spins shift back to planar suddenly upon approaching the Néel temperature (T N = 307 K). Density functional theory calculations support the idea that a shift in the Fermi level caused by doping is responsible for switching the material between two competing magnetic ground states. These results pave the way for developing easy switching of magnetic states in functional materials such as spintronic devices and topological insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Sturgeon and paddlefish (Acipenseridae) saggital otoliths are composed of the calcium carbonate polymorphs vaterite and calcite: acipenseridae otoliths are vaterite and calcite

The otoliths of modern fishes are most commonly comprised of the metastable aragonite polymorph of calcium carbonate (CaCO3); however, sturgeons have otoliths reportedly comprised of the least stable of the three most-common polymorphs, vaterite. In this study, we used neutron diffraction to characterize CaCO3 polymorph composition of lake sturgeon and paddlefish otoliths. Based on previous summaries of CaCO3 composition over fish evolutionary history, we hypothesized that sturgeon and paddlefish otoliths would have similar polymorph composition. We found that despite previous reports of sturgeon otoliths being comprised entirely of vaterite, that all otoliths we examined in this study also had a calcite fraction that ranged from 17.9+ 6.0 wt. % to 35.9 + 2.9 wt. %. We also conducted a grinding experiment that demonstrated that calcite fractions were due to biological variation and not an artifact of polymorph transformation during preparation. Our study provides the initial characterization of the polymorph composition of the otoliths of lake sturgeon, and paddlefish and also provides the first-ever report of otoliths of Acipenserids as having a calcite fraction.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Local molecular environment drives speciation and reactivity of ion complexes in concentrated salt solution

The speciation and reactivity of aqueous salt solutions are important for a wide variety of applications. However, application of this information is inhibited by broad disagreement about composition, mechanisms, and structure in concentrated solutions especially. Here, neutron diffraction with isotopic substitution measurements on aqueous zinc chloride solutions are used to calibrate molecular dynamics simulations that include effective electronic polarization. This allows us to probe the origin of speciation and reactivity of zinc chloride-water ion complexes, ZnCl x (H 2 O) y 2-x (x ≤ 4 and y ≤ 6), by comparing the reactivity of species in concentrated (4.5 m) and dilute (0.01 m) conditions. Within the concentrated solution, it is found that the extended solvation environment is dominated by solvent-separated ion complexes whose presence increases the free energy of activation for interconversion of species while simultaneously enhancing their thermodynamic stability. This concentration-dependent reactivity and stability suggests that other reactions, such as the nucleation of solid phases, will also be affected.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Effect of High-Density Nanoparticles on Recrystallization and Texture Evolution in Ferritic Alloys

Ferritic alloys are important for nuclear reactor applications due to their microstructural stability, corrosion resistance, and favorable mechanical properties. Nanostructured ferritic alloys having a high density of Y-Ti-O rich nano-oxides (NOs < 5 nm) are found to be extremely stable at high temperatures up to ~1100 °C. This study serves to understand the effect of a high density of nano-particles on texture evolution and recrystallization mechanisms in ferritic alloys of 14YWT (14Cr-3W-0.4Ti-0.21Y-Fe wt %) having a high density of nano-particles and dispersion-free FeCrAl (13Cr-5.2Al-0.05Y-2Mo-0.2Si-1Nb wt %). In order to investigate the recrystallization mechanisms in these alloys, neutron diffraction, electron backscattered diffraction, and in situ and ex situ transmission electron microscopy have been utilized. It has been observed that even though the deformation textures of both the 14YWT and FeCrAl alloys evolved similarly, resulting in either the formation (in FeCrAl alloy) or increase (in 14YWT) in γ-fiber texture, the texture evolution during recrystallization is different. While FeCrAl alloy keeps its γ-fiber texture after recrystallization, 14YWT samples develop a ε-fiber as a result of annealing at 1100 °C, which can be attributed to the existence of NOs. In situ transmission electron microscopy annealing experiments on 14YWT show the combination and growth of the lamellar grains rather than nucleation; however, the recrystallization and growth kinetics are slower due to NOs compared to FeCrAl.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Monitoring the refinement of crystal structures with {sup 15}N solid-state NMR shift tensor data

The {sup 15}N chemical shift tensor is shown to be extremely sensitive to lattice structure and a powerful metric for monitoring density functional theory refinements of crystal structures. These refinements include lattice effects and are applied here to five crystal structures. All structures improve based on a better agreement between experimental and calculated {sup 15}N tensors, with an average improvement of 47.0 ppm. Structural improvement is further indicated by a decrease in forces on the atoms by 2–3 orders of magnitude and a greater similarity in atom positions to neutron diffraction structures. These refinements change bond lengths by more than the diffraction errors including adjustments to X–Y and X–H bonds (X, Y = C, N, and O) of 0.028 ± 0.002 Å and 0.144 ± 0.036 Å, respectively. The acquisition of {sup 15}N tensors at natural abundance is challenging and this limitation is overcome by improved {sup 1}H decoupling in the FIREMAT method. This decoupling dramatically narrows linewidths, improves signal-to-noise by up to 317%, and significantly improves the accuracy of measured tensors. A total of 39 tensors are measured with shifts distributed over a range of more than 400 ppm. Overall, experimental {sup 15}N tensors are at least 5 times more sensitive to crystal structure than {sup 13}C tensors due to nitrogen’s greater polarizability and larger range of chemical shifts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Deformation Behavior of a Double Soaked Medium Manganese Steel with Varied Martensite Strength

The effects of athermal martensite on yielding behavior and strain partitioning during deformation is explored using in situ neutron diffraction for a 0.14C–7.14Mn medium manganese steel. Utilizing a novel heat treatment, termed double soaking, samples with similar microstructural composition and varied athermal martensite strength and microstructural characteristics, which composed the bulk of the matrix phase, were characterized. It was found that the addition of either as-quenched or tempered athermal martensite led to an improvement in mechanical properties as compared to a ferrite plus austenite medium manganese steel, although the yielding and work hardening behavior were highly dependent upon the martensite characteristics. Specifically, athermal martensite was found to promote continuous yielding and improve the work hardening rate during deformation. The results of this study are particularly relevant when considering the effect of post-processing thermal heat treatments, such as tempering or elevated temperature service environments, on the mechanical properties of medium manganese steels containing athermal martensite.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Elastic behavior of binary and ternary refractory multi-principal-element alloys

Elastic properties are essential to the mechanical performance of materials, and therefore, can be tuned to design high-performance materials. In this study, the elastic constants of the equiatomic ternary refractory multi-principal-element alloys, NbTiV, and MoNbV, were investigated, using in-situ neutron diffraction and first-principles calculations. The experimentally measured and theoretically predicted elastic constants show a good agreement. The alloying effect of adding Ti and Mo into NbV base alloy on the elastic constants is studied. Particularly, adding Ti elements into the NbV alloy results in the increase of the Zener anisotropy ratio from 0.59 to 0.99, leading to the formation of the elastically isotropic NbTiV alloy, while the addition of Mo decreases the anisotropy ratio to 0.52. Pugh’s ratio (B/G), Cauchy pressure (C 12 -C 44 ), and Poisson’s ratio (ν) are used to predict the brittle/ductile nature of the studied alloys, which is consistent with the mechanical results. The present work provides valuable insights into the design of ductile and strong refractory high-entropy alloys by tuning the elastic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structural aspects of glass-formation in Ni-Nb melts

We report on investigations of the static structure factors of glass-forming Ni{sub 59.5}Nb{sub 40.5} alloy melts by combination of the containerless processing technique of electrostatic levitation with neutron diffraction. By application of the isotopic substitution method, the full set of partial structure factors was determined. The short-range order in liquid Ni{sub 59.5}Nb{sub 40.5} is characterized by a large nearest neighbor coordination number of Z{sub NN} = 14.3 and a chemical short-range order with an affinity for the formation of heterogeneous Nb-Ni nearest neighbors. The structure factors observed here in the liquid state closely resemble those reported for amorphous Nb-Ni solids. The comparison with earlier results on the short-range structure in Zr-based glass-forming melts suggests that a large local density of packing, chemical order, and structural frustration are, amongst others, common structural properties of these metallic glass-forming systems, which favor glass-formation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

A residual stress study in similar and dissimilar welds

Residual strain distributions in similar and dissimilar welds were measured using neutron diffraction (ND) method. Then, using three strain components, three-dimensional stress states were calculated. The results were used to determine the effect of the martensitic phase transformation and material properties on residual stress (RS) distribution. It was observed that smaller longitudinal RS was induced in the low carbon steel side of dissimilar weld when compared to its similar weld. Also, it was found that the transverse RS near and within the weld zone (WZ) in dissimilar weld exhibited a distinctive trend, with tensile mode reaching the yield strength of the base metal (BM). In order to characterize the WZ in dissimilar weld, we deployed optical microscopy, hardness, and energy dispersive X-ray spectroscopy (EDAX). This study not only provides further insight into the RS state in similar and dissimilar welds; it also delivers important consequences of phase transformation in the latter case.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Frustration-mediated crossover from long-range to short-range magnetic ordering in Y 1 – x L u x BaC o 4 O 7

The R⁢BaC⁢o 4⁢ O 7 system is a prototype geometrically frustrated magnet in which kagome planes and triangular layers of Co-O tetrahedra interleave. For R=Y, an antiferromagnetic ground state is realized due to a frustration-breaking trigonal-orthorhombic phase transition. For R = Lu, however, a long-range ordered state has rarely, if ever, been reported despite a similar symmetry-breaking transition, albeit at a significantly lower temperature. To explore this dichotomy, we present a comprehensive magnetic and structural phase diagram for Y 1-x L⁢u x BaC⁢o 4 ⁢O 7 , established through complementary neutron diffraction and magnetization measurements. Our results outline the phase evolution of the nuclear structures in response to changes in composition and temperature. Further, the temperature of the trigonal (P⁢31⁢c) to orthorhombic (Pbn⁢2 1 ) transition, T s⁢1 , decreases monotonically with increasing Lu content from 310 K for x = 0.0 to 110 K for x = 1.0. In Lu-rich compositions (0.7 ≤ x ≤ 1.0), first-order structural transitions are observed with coexisting and competing orthorhombic Pbn⁢2 1 and metastable monoclinic Cc phases. For the magnetically ordered Y-rich compositions, T- and x-dependent refinements of the magnetic structure reveal an antiferromagnetic “ribbonlike” arrangement of Co spin pairs in both the triangular and the kagome layers. A gradual suppression of long-range magnetic order is observed with increasing the Lu content, accompanied by the development of short-range magnetic correlations present in all the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Thermal-history dependent magnetoelastic transition in (Mn,Fe){sub 2}(P,Si)

The thermal-history dependence of the magnetoelastic transition in (Mn,Fe){sub 2}(P,Si) compounds has been investigated using high-resolution neutron diffraction. As-prepared samples display a large difference in paramagnetic-ferromagnetic (PM-FM) transition temperature compared to cycled samples. The initial metastable state transforms into a lower-energy stable state when the as-prepared sample crosses the PM-FM transition for the first time. This additional transformation is irreversible around the transition temperature and increases the energy barrier which needs to be overcome through the PM-FM transition. Consequently, the transition temperature on first cooling is found to be lower than on subsequent cycles characterizing the so-called “virgin effect.” High-temperature annealing can restore the cycled sample to the high-temperature metastable state, which leads to the recovery of the virgin effect. A model is proposed to interpret the formation and recovery of the virgin effect.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Natural and accelerated CO{sub 2} binding kinetics in cement paste at different relative humidities

Natural carbonation and accelerated carbonation are compared in terms of CO{sub 2} combination. Thermogravimetrical analysis, neutron diffraction and weight measurements were used to quantify the amounts of CO{sub 2} in samples exposed to different CO{sub 2} and relative humidity (RH) conditions. An exponential equation is proposed to describe temporal evolution: combination rates and maximum values are obtained both for natural and accelerated processes. The influence of RH in these parameters is analyzed. At 100% CO{sub 2} an increase of RH from 53 to 75% diminishes the combination rate considerably, but increases slightly the maximum CO{sub 2} binding. At 0.5% CO{sub 2} both the rate and the maximum are higher for intermediate RH, with a linear relation between both variables. Equivalences between the different processes have been calculated: the amount of CO{sub 2} combined in 1 h at 100% CO{sub 2} and 65% RH carbonation is equivalent to approximately 36 days of natural exposure outside and 54 days inside.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Observation of a Large Magnetic Anisotropy and a Field-Induced Magnetic State in SrCo(VO 4 )(OH): A Structure with a Quasi One-Dimensional Magnetic Chain

A new member of the descloizite family, a cobalt vanadate, SrCo(VO 4 )(OH), has been synthesized as large single crystals using high-temperature and high-pressure hydrothermal methods. SrCo(VO 4 )(OH) crystallizes in the orthorhombic crystal system in space group P 2 1 2 1 2 1 with the following unit cell parameters: a = 6.0157(2) Å, b = 7.645(2) Å, c = 9.291(3) Å, V = 427.29(2) Å 3 , and Z = 4. It contains one-dimensional Co–O–Co chains of edge-sharing CoO 6 octahedra along the a -axis connected to each other via VO 4 tetrahedra along the b -axis forming a three-dimensional structure. The magnetic susceptibility of SrCo(VO 4 )(OH) indicates an antiferromagnetic transition at 10 K as well as unusually large spin orbit coupling. Single-crystal magnetic measurements in all three main crystallographic directions displayed a significant anisotropy in both temperature- and field-dependent data. Single-crystal neutron diffraction at 4 K was used to characterize the magnetically ordered state. The Co 2+ magnetic spins are arranged in a staggered configuration along the chain direction, with a canting angle that follows the tipping of the CoO 6 octahedra. The net magnetization along the chain direction, resulting in ferromagnetic coupling of the a -axis spin components in each chain, is compensated by an antiferromagnetic interaction between nearest neighbor chains. A metamagnetic transition appears in the isothermal magnetization data at 2 K along the chain direction, which seems to correspond to a co-alignment of the spin directions of the nearest neighbor chain. We propose a phenomenological spin Hamiltonian that describes the canted spin configuration of the ground state and the metamagnetic transition in SrCo(VO 4 )(OH).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Effects of Aluminum Plate Initial Residual Stress on Machined-Part Distortion

Dimensional tolerances for high-speed-machined aluminum products continue to tighten due to the demand for automated assembly of complex monolithic parts in aerospace and other industries. Understanding the contribution of inherent residual stress in wrought Al 7050-T7451 plate, common in aircraft manufacture, to distortion of high-aspect-ratio machined parts is critical but remains problematic due to the alloy's low residual stress magnitude over large geometries. Prior investigations into residual stress effects on machined part distortion suffer inadequate characterizations of the wrought material stress field, either because of low fidelity due to “slitting” methods, confounding effects in machined-layer removal methods, or small sample size when using neutron diffraction (ND). In this work, inherent residual stress is measured via ND at 860 locations in a 90.5 mm thick Al 7050-T7451 plate having dimensions 399 mm in the rolling direction and 335 mm in the transverse direction. Unlike prior studies, the ND residual stress is reconstructed using an iterative algorithm to ensure fully compatible, equilibrated 3D field prior to examining its effect on distortion. Further, the findings from simulations and experiments show that inherent residual stress alone could distort a high-aspect-ratio part beyond aerospace industry requirements, that slitting measurements may not sufficiently characterize residual stress for predicted distortion, and that parts machined from different plate thickness locations could exhibit reversed distortion patterns. Thus, research into distortion prediction that considers machining should carefully characterize and reconstruct inherent residual stress so that the coupled machining effects are accurately modeled.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tuning the melting point and phase stability of rare-earth oxides to facilitate their crystal growth from the melt

The challenge of growing rare-earth (RE) sesquioxide crystals can be overcome by tailoring their structural stability and melting point via composition engineering. This work contributes to the advancement of the field of crystal growth of high-entropy oxides. A compound with only small REs (Lu,Y,Ho,Yb,Er) 2 O 3 maintains a cubic C-type structure upon cooling from the melt, as observed via in-situ high-temperature neutron diffraction on aerodynamically levitated samples. On the other hand, a compound with a mixture of small and large REs (Lu,Y,Ho,Nd,La) 2 O 3 crystallizes as a mixture of a primary C-type phase with an unstable secondary phase. Crystals of compositions (Lu,Y,Ho,Nd,La) 2 O 3 and (Lu,Y,Gd,Nd,La) 2 O 3 were grown by the micro-pulling-down (mPD) method with a single monoclinic B-type phase, while a powder of (Lu,Y,Ho,Yb,Er) 2 O 3 did not melt at the maximum operating temperature of an iridium-rhenium crucible. The minimization of the melting point of the two grown crystals is attributed to the mismatch in cation sizes. The electron probe microanalysis reveals that the general element segregation behavior in the crystals depends on the composition.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Magnetic ordering in Ho{sub 2}Fe{sub 2}Si{sub 2}C

We have used neutron diffraction and {sup 57}Fe Mössbauer spectroscopy, complemented by magnetisation and specific heat measurements, to examine the magnetic ordering of Ho{sub 2}Fe{sub 2}Si{sub 2}C. We have established that Ho{sub 2}Fe{sub 2}Si{sub 2}C orders antiferromagnetically below T{sub N} = 16(1) K with a magnetic structure involving ordering of the Ho sublattice along the b-axis with a propagation vector k=[0 0 1/2 ]. {sup 57}Fe Mössbauer spectra collected below T{sub N} show no evidence of a magnetic splitting, demonstrating the absence of long range magnetic ordering of the Fe sublattice. A small line broadening is observed in the {sup 57}Fe spectra below T{sub N}, which is due to a transferred hyperfine field—estimated to be around 0.3 T at 10 K—from the Ho sublattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Energy absorption of architectured PrintCast interpenetrating composites in tension

Additively manufactured (AM) metal-metal composites consisting of PrintCasted 316 L austenitic stainless-steel lattice structures infiltrated with A356 casting alloy, have recently been developed for use in high energy absorption systems with potential applications ranging from static load bearing to dynamic blast containment structures. This system has a unique mechanical behavior as the volume fraction of lattice increases showing a transition from localized to de-localized failure and dramatic increase in energy absorption capability. In this work, PrintCast A356/316 L composite tensile specimens were produced with lattice volume fractions ranging from 20 % to 50 % to capture the range of this behavior. Finite element simulations support neutron diffraction measurements of stress state. Results illustrate that in tension, the reinforcement material is in tension while the matrix support material is in compression, information offering significant insight into the transition to de-localized failure. Moreover, the simulation results provide further insight into how interfacial bonding (or lack of bonding) affects the energy absorption capabilities of the PrintCast composites.

36 MATERIALS SCIENCE↗