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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High capacity ammonia adsorption in a robust metal–organic framework mediated by reversible host–guest interactions

To understand the exceptional adsorption of ammonia (NH 3 ) in MFM-300(Sc) (19.5 mmol g -1 at 273 K and 1 bar without hysteresis), we report a systematic investigation of the mechanism of adsorption by a combination of in situ neutron powder diffraction, inelastic neutron scattering, synchrotron infrared microspectroscopy, and solid-state 45 Sc NMR spectroscopy. These complementary techniques reveal the formation of reversible host–guest supramolecular interactions, which explains directly the observed excellent reversibility of this material over 90 adsorption–desorption cycles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

The effect of rare earth (RE 3+ ) ionic radii on transparent lanthanide-tellurite glass-ceramics: correlation between ‘hole-formalism’ and crystallization

Rare earth (RE) doped transparent tellurite glass-ceramics (GCs) are widely explored for their application as advanced photonic materials. Specifically, the growth of RE based “anti-glass” crystalline phases in transparent GCs enhances their effective functionality. Enormous studies on the properties of GCs revealed that optimization of glass composition and heat-treatment schedule are the foremost factors that affect the transparency of the GCs. Nevertheless, the direct effect of RE 3+ ions on the crystallization mechanism of glass has hardly been reported. Therefore, a base glass of the composition La 2 O 3 –Gd 2 O 3 –TiO 2 –TeO 2 (LGTT) is doped with RE 3+ ions (Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Tb 3+ , and Dy 3+ ) with varied ionic radii. Rietveld refinement from XRD of GCs confirms that (La/Gd) 2 Te 6 O 15 phases are precipitated, where dopants Ce, Pr and Nd occupy La sites, while Sm, Eu, Tb, and Dy occupy Gd sites. The configurational heat-capacity (ΔC p ) from DSC is found to be lower for larger ionic radii REs (Ce, Pr, Nd) than smaller ionic radii REs (Sm, Eu, Tb, Dy) thereby exhibiting higher chemical ordering followed by faster crystal growth rate in the former. However, the transparency retention profile of different RE-doped GCs follows the trend Eu:Tb > Sm:Dy > Nd > Pr > Ce, confirming the ionic radii effect. In addition to the ionic radii effect, in this work, we propose a ‘Hole-Formalism’ concept to explain the observed trend. It is further corroborated with an identical neutron diffraction pattern and ΔC p values for these ion pairs Sm 3+ : Dy 3+ (4f 5 : 4f 9 ) and Eu 3+ : Tb 3+ (4f 6 : 4f 8 ) results in a similar crystallization mechanism, transmission profile and fine-scale microstructures of these RE-based tellurite GCs.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Complex defect chemistry of hydrothermally-synthesized Nb-substituted β$'$-LiVOPO 4

Lithium vanadyl phosphate (LiVOPO 4 ) is a next-generation multielectron battery cathode that can intercalate up to two Li-ions per V-ion through the redox couples of V 4+ /V 3+ and V 5+ /V 4+ . However, its rate capacity is undermined by the sluggish Li-ion diffusion in the high-voltage region (4 V for V 5+ /V 4+ redox). Nb substitution was used to expand the crystal lattice to facilitate Li-ion diffusion. Here, in this work, Nb substitution was achieved via hydrothermal synthesis, which resulted in a new, lower symmetry β'-LiVOPO 4 phase with preferential Nb occupation of one of the two V sites. This phase presents complex defect chemistries, including cation vacancies and hydrogen interstitials, characterized by a combination of X-ray and neutron diffraction, elemental and thermogravimetric analyses, X-ray absorption spectroscopy, and magnetic susceptibility measurements. The Nb-substituted samples demonstrated improved capacity retention and rate capabilities in the high-voltage region, albeit an enlarged voltage hysteresis related to a partial V 4+ /V 3+ redox reaction, as evidenced by ex situ X-ray absorption spectroscopy and pair distribution function analysis. This work highlights the importance of understanding the complex defect chemistry and its consequence on electrochemistry in polyanionic intercalation compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Large magnetic anisotropy of a decorated spin-chain system K 2 Co 3 (MoO 4 ) 3 (OH) 2

The magnetic structure of K 2 Co 3 (MoO 4 ) 3 (OH) 2 is studied in detail. The material has a half-sawtooth one-dimensional (1-D) structure containing two unique Co 2+ ions, one in the chain backbone and one on the apex of the sawtooth creating a series of isosceles triangles along the b-axis. These triangles can be a source of magnetic frustration. The ability to grow large single crystals enables detailed magnetic measurements with the crystals oriented in a magnetic field along the respective axes. It has a Curie–Weiss temperature θ CW of 5.3(2) K with an effective magnetic moment of 4.8(3)μ B /Co. The material is highly anisotropic with a sharp antiferromagnetic ordering transition at 7 K with a metamagnetic transition at 2 kOe. Neutron diffraction was used to determine the magnetic structure and revealed a magnetic structure with canted spins along the backbone of the chain while spins along the sawtooth caps maintained a colinear orientation, arranging antiferromagnetically relative to the backbone spins. In conclusion, the parallel chains arrange antiferromagnetically relative to each other along the c-axis and ferromagnetically along the a-axis.

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

Oxygen redox activities governing high-voltage charging reversibility of Ni-rich layered cathodes

A schematic illustration indicative of the improved structural reversibility through stabilizing oxidized oxygen by Al doping. The chemical reactions and phase transitions at high voltages are generally considered to determine the electrochemical properties of high-voltage layered cathodes such as Ni-rich rhombohedral oxides. Even if significantly higher SOCs (states-of-charge) are utilized above the capability of transition metal redox (primarily Ni and Co), the effect of oxygen redox on Ni-rich rhombohedral oxides still looks mysterious thereby necessitating research that can clarify the relationship between redox reactions and phase transitions. Here, we performed a comprehensive and comparative study of the cationic and anionic redox reactions, as well as the structural evolution of a series of commercial Ni-rich layered oxides with and without Al doping. We combined the results from X-ray spectroscopy, operando electrochemical mass spectrometry, and neutron diffraction with electrochemical properties and thereby revealed the different oxygen redox activities associated with structural and electrochemical degradations. We reveal that Al doping suppresses the irreversible oxygen release but enhances the lattice oxygen oxidization. With this modulated oxygen redox activity, the Ni-rich layered oxides’ notorious H2–H3 structural phase transition becomes highly reversible. Our findings disentangle the different oxygen redox activities during high-voltage cycling and clarify the role of dopants in the Ni-rich layered oxides in terms of structural and electrochemical stability, shedding light on the future direction of optimizing layered cathode materials for safer high energy-density secondary batteries.

Lee, Gi-Hyeok↗
DOE OSTI2024

Synthesis and symmetry of perovskite oxynitride CaW(O,N) 3

Perovskite oxynitrides, in addition to being promising electrocatalysts and photoabsorbers, present an interesting case study in crystal symmetry. Full or partial ordering of the O and N anions affects global symmetry and influences material performance and functionality; however, anion ordering is challenging to detect experimentally. In this work, we synthesize a novel perovskite oxynitride CaW(O,N) 3 and characterize its crystal structure using both X-ray and neutron diffraction. Through co-refinement of the diffraction patterns with a range of literature and theory-derived model structures, we demonstrate that CaW(O,N) 3 adopts an orthorhombic Pnma average structure and exhibits octahedral distortion with evidence for preferred anion site occupancy. However, through comparison with a large, low-symmetry unit cell, we identify the presence of disorder that is not fully accounted for by the high-symmetry model. We compare CaW(O,N) 3 with SrW(O,N) 3 to demonstrate the broader presence of such disorder and identify contrasting features in the electronic structures. This work signifies an updated perspective on the inherent crystal symmetry present in perovskite oxynitrides.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

Magnetic skyrmions are topologically protected, nanoscale whirls of the spin configuration that tend to form hexagonally ordered arrays. As a topologically non-trivial structure, the nucleation and annihilation of the skyrmion, as well as the interaction between skyrmions, varies from conventional magnetic systems. Recent works have suggested that the ordering kinetics in these materials occur over millisecond or longer timescales, which is unusually slow for magnetic dynamics. The current work investigates the skyrmion ordering kinetics, particularly during lattice formation and destruction, using time-resolved small angle neutron scattering (TR-SANS). Evaluating the time-resolved structure and intensity of the neutron diffraction pattern reveals the evolving real-space structure of the skyrmion lattice and the timeframe of the formation. Measurements were performed on three prototypical skyrmion materials: MnSi, (Fe,Co)Si, and Cu 2 OSeO 3 . To probe lattice formation and destruction kinetics, the systems were prepared in the stable skyrmion state, and then a square-wave magnetic field modulation was applied. The measurements show that the skyrmions quickly form ordered domains, with a significant distribution in lattice parameters, which then converge to the final structure; the results confirm the slow kinetics, with formation times between 10 ms and 99 ms. Comparisons are made between the measured formation times and the fundamental material properties, suggesting the ordering temperature, saturation magnetization and magnetocrystalline anisotropy may be driving the timeframes. Micromagnetic simulations were also performed and support a scaling of the kinetics with sample volume, a behavior which is caused by the reconciling of misaligned domains.

Liyanage, W. L. N. C.↗
DOE OSTI2024

Effects of Al concentration on the structure and conductivity of lithium lanthanum zirconium oxide

Cubic Li 7-3x Al x La 3 Zr 2 O 12 (LLZO) is a promising, next-generation solid electrolyte due to its stability with Li-metal and high bulk conductivity (~1 mS cm -1 ). However, the source of the high conductivity is not completely understood. In this work, we address this key knowledge gap through the integration of elemental analysis, neutron diffraction sensitive to Li and O atoms, and impedance spectroscopy to understand the structure–property correlations for LLZO. We show the metal–oxygen framework structure remains constant with variation in Al substitution, resulting in a constant activation energy of ~0.35 eV and little effect on the bulk conductivity. Instead, Li concentration, Al blocking and trapping of mobile defects, and Li–Li nearest neighbor interactions largely control the Al substituted LLZO bulk conductivity, resulting in decreases from 0.73 to 0.22 mS cm -1 as the Al concentration increases from 0.17 to 0.32 mol. These results differ from those of Ta substituted LLZO, where the framework structure and Li–Li site distances play large roles in controlling the conductivity. The increased understanding of the controlling factors of conductivity allows for greater ability to tailor the design of and substitution into the LLZO structure for improved conductivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Crystal structure of Cu2Zn(GexSi1−x)Se4 solid solution: the kesterite to wurtz–kesterite structural phase transition

Developing low-cost, sustainable, and environmentally friendly top absorber layers for tandem solar cells is essential to advancing photovoltaic technologies and accelerating the transition to renewable energy. In this work, we explore the potential of tetravalent (Cu2Zn(GexSi1−x)Se4) cation mutations in chalcogenide compound semiconductors with the aim of finding a material with increased band gap and reduced structural disorder. A combination of high-resolution synchrotron powder diffraction and neutron powder diffraction was used to determine the atomic positions and monoclinic angles in monoclinic wurtz–kesterite type Cu2Zn(GexSi1−x)Se4 mixed crystals as well as to determine the cation distribution in the crystal structure of Ge-rich kesterite-type and Si-rich wurtz–kesterite type mixed crystals. These investigations enabled us to deduce the structural transition scenario within the Cu2Zn(GexSi1−x)Se4 series. The transition occurs via a region where two phases with different crystal structures, tetragonal and monoclinic and thus a different distortion of the coordination tetrahedra, but the same cation distribution within the element specific cation sites co-exist. Thus, the structural transition between the kesterite and the wurtz–kesterite structure within the Cu2Zn(GexSi1−x)Se4 series is a distortion driven transition. The study identifies cation mutation in quaternary chalcogenides as a promising strategy beyond chalcopyrites and kesterites for low cost and environmentally friendly top absorbers in tandem solar cells.

Gurieva, Galina [Helmholtz Center Berlin for Mater↗
DOE OSTI2018

Equation of state, phase stability, and phase transformations of uranium-6 wt.% niobium under high pressure and temperature

In-situ time-of-flight neutron diffraction experiments were conducted on the uranium-niobium alloy with 6 wt. % Nb (U–6Nb) at pressures up to 4.7 GPa and temperatures up to 1073 K. Upon static compression at room temperature, the monoclinic structure of U–6Nb (α" U–6Nb) remains stable up to the highest experimental pressure. Based on the pressure-volume measurements at room temperature, the least-squares fit using the finite-strain equation of state (EOS) yields an isothermal bulk modulus of B 0 = 127±2 GPa for the α"-phase of U–6Nb. The calculated zero-pressure bulk sound speed from this EOS is 2.706±0.022 km/s, which is in good agreement with the linear extrapolation of the previous Hugoniot data above 12 GPa for α" U–6Nb, indicating that the dynamic response under those shock-loading conditions is consistent with the stabilization of the initial monoclinic phase of U-6Nb. Upon heating at ambient and high pressures, the metastable α" U–6Nb exhibits complex transformation paths leading to the diffusional phase decomposition, which are sensitive to applied pressure, stress state, and temperature-time path. These findings provide new insight into the behavior of atypical systems such as U-Nb and suggest that the different U-Nb phases are separated by rather small energies and hence highly sensitive to compositional, thermal, and mechanical perturbations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

The magnetic order of a manganese vanadate system with two-dimensional striped triangular lattice

Results of magnetization and neutron diffraction measurements of the manganese vanadate system Mn 5 (VO 4 ) 2 (OH) 4 are reported. The crystal structure of this compound contains triangular [Mn 3 O 13 ] building blocks that produce two-dimensional Mn 2+ magnetic networks with striped triangular topologies. The Mn sheets are connected through the nonmagnetic vanadate tetrahedra extending along the a-axis. Magnetization measurements performed on single crystals reveal the onset of a long-range antiferromagnetic order below approximately 45 K. The magnetic structure is Néel-type with nearest-neighbor Mn atoms coupled via three or four antiferromagnetic bonds. The magnetic moments are confined within the layers and are oriented parallel to the b direction. In conclusion, the magnitudes of ordered moments are reduced, presumably by geometrical frustration and the low-dimensionality of the lattice structure.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Angular alignment and fidelity of neutron phase-gratings for improved interferometer fringe visibility

The recent development of phase-grating moiré neutron interferometry promises a wide range of impactful experiments from dark-field imaging of material microstructure to precise measurements of fundamental constants. However, the contrast of 3% obtained using this moiré interferometer was well below the theoretical prediction of 30% using ideal gratings. It is suspected that non-ideal aspects of the phase-gratings was a leading contributor to this deficiency and that phase-gratings needed to be quantitatively assessed and optimized. Here we characterize neutron diffraction from phase-gratings using Bragg diffraction crystals to determine the optimal phase-grating orientations. We show well-defined diffraction peaks and explore perturbations to the diffraction peaks and the effects on interferometer contrast as a function of grating alignment. This technique promises to improve the contrast of the grating interferometers by providing in-situ aides to grating alignment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Thermal expansion coefficients of high thermal conducting BAs and BP materials

Recently reported very high thermal conductivities in cubic boron arsenide (BAs) and boron phosphide (BP) crystals could potentially provide a revolutionary solution in the thermal management of high power density devices. To fully facilitate such an application, the compatible coefficient of thermal expansion (CTE) between the heat spreader and the device substrate, in order to minimize the thermal stress, needs to be considered. Here, we report our experimental CTE studies of BAs and BP in the temperature range from 100 K to 1150 K, through a combination of X-ray single crystal diffraction and neutron powder diffraction. Here, we demonstrated that the room temperature CTEs, 3.6 ± 0.15 × 10 –6 /K for BAs and 3.2 ± 0.2 × 10 –6 /K for BP, are more compatible with most of the semiconductors including Si and GaAs, in comparison with diamond, and thus could be better candidates for the future heat spreader materials in power electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Significant enhancement of magnetocaloric effect in a NiMnCuGa Heusler alloy through textural modification

Magnetocaloric materials are of increasing interest to bring magnetic refrigeration to everyday households and drastically impact the energy demands for temperature control devices. In this work, a polycrystalline Heusler alloy of composition Ni2Mn0.76Cu0.24Ga with coinciding structural and magnetic transformation temperatures was subjected to compressive stress assisted thermal cycling (SATC) to enhance the magnetic properties by inducing a preferred orientation in the martensite. Isofield magnetization measurements showed a sharpening of the transformation between ferromagnetic martensite and paramagnetic austenite due to SATC. In isothermal magnetization measurements, SATC was seen to increase the magnetostructural coupling. With a 2 T applied magnetic field, the magnetocaloric effect (MCE) increased from ∼10 to ∼25 J/kg K and the refrigeration capacity (RC) almost doubled due to SATC. Heat capacity measurements were largely unaffected by SATC. The change in adiabatic temperature was estimated by using Cp and change in magnetic entropy (ΔSM) calculations. SATC was seen to increase ΔTad from ∼1.2 K to 2 K for an applied magnetic field of 2 T. Neutron diffraction measurements revealed highly textured martensite in the as received state that rotated to a more ideal preferred orientation after SATC that enhanced the magnetostructural transformation; and thus, improving the MCE and ΔTad.

McLeod, M. V. (ORCID:0000000329883516)↗
DOE OSTI2023

The structure and electronic properties of tetrahedrally bonded hydrogenated amorphous carbon

In this work, we have synthesized hydrogenated and deuterated amorphous carbon materials that have a density, 2.7 ± 0.1 g/cm 3 , consistent with almost entirely tetrahedral bonding. In hydrogen-free tetrahedral amorphous carbon, the presence of a minority of sp2 bonded atoms leads to localized states that could be passivated with hydrogen by analogy with hydrogenated amorphous silicon. Neutron diffraction analysis demonstrated that the local bonding environment is consistent with ab initio models of high density hydrogenated tetrahedral amorphous carbon and with the related tetrahedral molecular structure neopentane. The optical bandgap of our material, 4.5 eV, is close to the bandgap in the density of states determined by scanning tunneling spectroscopy (4.3 eV). This bandgap is considerably larger than that of hydrogen-free tetrahedral amorphous carbon, confirming that passivation of sp 2 associated tail-states has occurred. Both the structural and electronic measurements are consistent with a model in which the tetrahedrally bonded carbon regions are terminated by hydrogen, causing hopping conductivity to dominate.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Flat-band tuning and emergent itinerant magnetism in Sr(Co 1− x Pd x ) 2 As 2

The interplay between magnetism and flat-band (FB) instability is a central theme in quantum materials research. A striking example is the emergence of magnetic order in a nominally nonmagnetic compound when a flat band is tuned near the Fermi energy (E F ). Here, in this study, we investigate this phenomenon in the Pauli paramagnet SrCo 2 As 2 , where an FB associated with Co e g orbitals lies close to E F . Remarkably, a minute substitution of the nonmagnetic element Pd onto the Co site (~2%) induces antiferromagnetic order with a transition temperature as high as T N = 25 K. Temperature- and magnetic-field-dependent magnetic and transport measurements, complemented by zero-field neutron diffraction, reveal a helical magnetic order for x ≤ 0.10 in Sr(Co 1−x Pd x ) 2 As 2 , transitioning to a complex ferromagnetic state at higher Pd concentrations. Spectroscopic evidence and theoretical band structure calculations demonstrate that electron doping shifts the flat band closer to E F , significantly enhancing the Stoner parameter. This enhancement drives a strong ferromagnetic instability, leading to helical magnetic ordering dominated by in-plane ferromagnetic interactions. The emergence of robust magnetic ordering through substitution with nonmagnetic elements is a unique phenomenon that underscores the pivotal role of flat-band instability in tuning magnetism in itinerant systems.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetic Order and Its Interplay with Structure Phase Transition in van der Waals Ferromagnet VI 3

We show that Van der Waals magnet VI 3 demonstrates intriguing magnetic properties that render it great for use in various applications. However, its microscopic magnetic structure has not been determined yet. Here, we report neutron diffraction and susceptibility measurements in VI 3 that revealed a ferromagnetic order with the moment direction tilted from the c-axis by ~36° at 4 K. A spin reorientation accompanied by a structure distortion within the honeycomb plane is observed, before the magnetic order completely disappears at $T_C$ = 50 K. The refined magnetic moment of ~1.3$μ_B$ at 4 K is much lower than the fully ordered spin moment of 2$μ_B$/V 3+ , suggesting the presence of a considerable orbital moment antiparallel to the spin moment and strong spin–orbit coupling in VI 3 . This results in strong magnetoelastic interactions that make the magnetic properties of VI 3 easily tunable via strain and pressure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗