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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The phononic and charge density wave behavior of entire rare-earth tritelluride series with chemical pressure and temperature

Here, we present comprehensive phononic and charge density wave properties (CDW) of rare-earth van der Waals tritellurides through temperature dependent angle-resolved Raman spectroscopy measurements. All the possible rare-earth tritellurides (RTe3) ranging from R = La–Nd, Sm, Gd–Tm were synthesized through a chemical vapor transport technique to achieve high quality crystals with excellent CDW characteristics. Raman spectroscopy studies successfully identify the emergence of the CDW state and transition temperature (TCDW), which offers a non-destructive method to identify their CDW response with micron spatial resolution. Temperature dependent Raman measurements further correlate how the atomic mass of metal cations and the resulting chemical pressure influence its CDW properties and offer detailed insight into the strength of CDW amplitude mode-phonon coupling during the CDW transition. Angle-resolved Raman measurements offer the first insights into the CDW-phonon symmetry interplay by monitoring the change in the symmetry of phonon mode across the CDW transition. Overall results introduce the library of RTe3 CDW materials and establish their characteristics through the non-destructive angle-resolved Raman spectroscopy technique.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Antiferromagnetic order and its interplay with superconductivity in CaK(Fe$_{1-x}$Mn$_x$) 4 As 4

The magnetic order for several compositions of CaK(Fe$_{1-x}$Mn$_x$) 4 As 4 has been studied by nuclear magnetic resonance (NMR), Mössbauer spectroscopy, and neutron diffraction. Our observations for the Mn-doped 1144 compound are consistent with the hedgehog spin vortex crystal (hSVC) order which has previously been found for Ni-doped CaKFe 4 As 4 . The hSVC state is characterized by the stripe-type propagation vectors $(\pi\,0)$ and $(0\,\pi)$ just as in the doped 122 compounds. The hSVC state preserves tetragonal symmetry at the Fe site, and only this SVC motif with simple antiferromagnetic (AFM) stacking along $\ c$ is consistent with all our observations using NMR Mössbauer spectroscopy, and neutron diffraction. We find that the hSVC state in the Mn-doped 1144 compound coexists with superconductivity (SC), and by combining the neutron scattering and Mössbauer spectroscopy data we can infer a quantum phase transition, hidden under the superconducting dome, associated with the suppression of the AFM transition temperature ($T_N$) to zero for $x$ ≈ 0.01. In addition, unlike several 122 compounds and Ni-doped 1144, the ordered magnetic moment is not observed to decrease at temperatures below the superconducting transition temperature ($T_c$).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Electronic band structure and magnetism of CoFeV 0.5 Mn 0.5 Si

Half-metallic Heusler alloys have attracted significant attention due to their potential application in spin-transport-based devices. We have synthesized one such alloy, CoFeV 0.5 Mn 0.5 Si, using arc melting and high-vacuum annealing at 600 °C for 24 hours. First principles calculation indicates that CoFeV 0.5 Mn 0.5 Si shows a nearly half-metallic band structure with a degree of spin polarization of about 93%. In addition, this value can be enhanced by the application of tensile strain. The room temperature x-ray diffraction patterns are indexed with the cubic crystal structure without secondary phases. The annealed sample shows ferromagnetic order with the Curie temperature well above room temperature ( T c = 657 K) and a saturation magnetization of about 92 emu/g. Our results indicate that CoFeV 0.5 Mn 0.5 Si has a potential for room temperature spin-transport-based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Total-scattering pair-distribution function analysis of zinc from high-energy synchrotron data

The crystal structure of zinc metal deviates from the ideal hexagonal close packing structure by a significantly increased axial ratio (c/a). The local atomic structure of zinc metal is investigated using the total scattering atomic pair distribution function (PDF) analysis based on X-ray powder diffraction data collected at ambient conditions. The X-ray total scattering PDF analysis confirms that the crystal structure of zinc can be described in terms of wurtzite structure, but with an anomalously atomic displacement parameters U 33 , indicating a significant displacement disorder along the c-axis. For the long r-range PDF refinements, the thermal motion of zinc shows a notable anisotropy as expressed by the ratio U 33 /U 11 of 2.5 at ambient conditions. This average distortion level along the c-axis, was not reflected locally for the features below 5.0 Å as it fits the high r region. Based on PDF refinements over different r-ranges, we measure an interesting increase of the U 33 value with decreasing the r-range of the refinement. Finally, this suggests that the local structure features in zinc metal differ from the average structure ones.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Temperature-dependent Structural and Spectroscopic Studies of (Bi 1– x Fe x )FeO 3

We report on temperature-dependent structural and spectroscopic features of (Bi 1–x Fe x )FeO 3 perovskite for x = 0.15 and 0.25. Samples were synthesized by heating quantum crystalline precursors obtained by the polyol method. Crystal structures of each composition were obtained from in-house X-ray, synchrotron X-ray, and time-of-flight neutron powder diffraction data Rietveld refinements. Partial replacement of the Bi site by the Fe 3+ cation significantly changes the crystal physicochemical properties, such as thermal expansion, polyhedral distortion, Debye temperature, and vibrational and magnetic properties. Whereas BiFeO 3 is multiferroic, both Bi 0.85 Fe 0.15 FeO 3 and Bi 0.75 Fe 0.25 FeO 3 are found to be superparamagnetic, as observed by temperature-dependent Mössbauer and SQUID measurements. Lattice thermal expansion was modeled using the Debye–Einstein-anharmonicity approach. Debye temperatures obtained from the mean-squared atomic displacement parameter and lattice thermal expansion are compared. Furthermore, temperature dependence of selective Raman modes is also analyzed.

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

Flat-band magnetism and helical magnetic order in Ni-doped SrCo 2 As 2

A series of Sr(Co 1-$x$ Ni $x$ ) 2 As 2 single crystals was synthesized, allowing a comprehensive phase diagram with respect to field, temperature, and chemical substitution to be established. Our neutron diffraction experiments revealed a helimagnetic order with magnetic moments ferromagnetically aligned in the ab plane and a helimagnetic wave vector of $q$= (0,0,0.56) for $x$= 0.1 . Finally, the combination of neutron diffraction and angle-resolved photoemission spectroscopy measurements shows that the tuning of a flat band with $d_{x^2-y^2}$ orbital character drives the helimagnetism and indicates the possibility of a quantum order-by-disorder mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Compressive transmission microscopy

Transmission microscopy imaging systems include a mask and/or other modulator situated to encode image beams, e.g., by deflecting the image beam with respect to the mask and/or sensor. The beam is modulated/masked either before or after transmission through a sample to induce a spatially and/or temporally encoded signal by modifying any of the beam/image components including the phase/coherence, intensity, or position of the beam at the sensor. For example, a mask can be placed/translated through the beam so that several masked beams are received by a sensor during a single sensor integration time. Images associated with multiple mask displacements are then used to reconstruct a video sequence using a compressive sensing method. Another example of masked modulation involves a mechanism for phase-retrieval, whereby the beam is modulated by a set of different masks in the image plane and each masked image is recorded in the diffraction plane.

42 ENGINEERING↗
DOE OSTI2019

Method and apparatus for wavefront sensing

A method for performing optical wavefront sensing includes providing an amplitude transmission mask having a light input side, a light output side, and an optical transmission axis passing from the light input side to the light output side. The amplitude transmission mask is characterized by a checkerboard pattern having a square unit cell of size Λ. The method also includes directing an incident light field having a wavelength λ to be incident on the light input side and propagating the incident light field through the amplitude transmission mask. The method further includes producing a plurality of diffracted light fields on the light output side and detecting, at a detector disposed a distance L from the amplitude transmission mask, an interferogram associated with the plurality of diffracted light fields. The relation is satisfied, where n is an integer greater than zero.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Effect of Annealing Temperature on Structure and Magnetic Properties of Zn{sub 0.94}Mg{sub 0.01}Mn{sub 0.05}O Nanoparticles

Structural and magnetic characteristics of Zn{sub 0.94}Mg{sub 0.01}Mn{sub 0.05}O (ZnMgMnO) nanoparticles synthesized by Sol-Gel preparation technique in a wide temperature range were reported. The influence of annealing temperature on the crystal structure of ZnMgMnO nanoparticles was figured out by X-ray diffraction technique (XRD). To optimize the annealing temperature and reveal the particle formation and size, Scanning Electron Microscope (SEM) imaging technique was performed. The required stoichiometry of the synthesized samples was obtained by an energy dispersive X-ray analysis technique (EDX). Quantum Design Vibrating Sample Magnetometer (QDVSM) tool was used for the magnetic characterizations of Zn{sub 0.94}Mg{sub 0.01}Mn{sub 0.05}O composition. Magnetization measurements as a function of magnetic field (M-H) were performed in the magnetic field up to 10 kOe. Temperature dependence of magnetization measurements (M-T) was taken between 10 and 320 K temperature ranges.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Frustrated Magnetism and Ferroelectricity in a Dy 3+ -Based Triangular Lattice

Triangular lattice magnets have attracted extensive research interest because they are potential hosts for geometrically frustrated magnetism and strong quantum fluctuations. Here, utilizing a laser floating zone technique, we report the first-time successful growth of a DyInO 3 sizable crystal, which contains Dy3+-based triangular layers. The fine-tuning of Indium stoichiometry was found to be the key factor in the stabilization of the desired hexagonal phase. The X-ray diffraction study of the crystal structure reveals a non-centrosymmetric P6 3mc space group. Switchable polarization, i.e., ferroelectricity, and ferroelectric domain configuration are experimentally demonstrated at room temperature. Anisotropic magnetic and thermodynamic measurements unveil antiferromagnetic interactions, the absence of long-range ordering down to 0.1 K, and a possible doublet ground state, indicating a strongly frustrated magnetism. Our findings suggest that the DyInO 3 crystal is an excellent platform for studying emergent phenomena and their interplay with coherent topological defects in the quantum realm.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Probing the lattice structure of dynamically compressed and released single crystal iron through the alpha to epsilon phase transition

In this work, experiments using broadband Laue x-ray diffraction (XRD) were used to examine the lattice structure of dynamically compressed [100]-oriented single crystal iron samples at the Dynamic Compression Sector at the Advanced Photon Source. These experiments used 1 μm thick iron single crystal samples sandwiched between a polyimide ablator and a polycarbonate window. A 100 J, 10 ns duration laser pulse incident on the polyimide ablator was used to shock compress the iron samples to initial stresses greater than 25 GPa, exceeding the ~13 GPa alpha (body-centered-cubic or bcc structure) to epsilon (hexagonal-close-packed or hcp structure) phase transition stress. XRD measurements were performed at various times relative to the shock wave entering the iron sample: early times, <~150 ps while the initial shock waves propagated through the iron; intermediate times, after the iron equilibrated with the ablator and window reaching a plateau stress state (12 or 17 GPa) lasting several nanoseconds; and late times, during uniaxial strain release. The early time measurements show that in <~150 ps, the high-pressure hcp phase is relaxed with a c/a ratio of 1.61, contrary to previous laser shock experiments where a c/a ratio of 1.7 was inferred. In the plateau stress state and partially released states, XRD measurements showed that the hcp structure retained a c/a ratio of 1.61 with no observable changes in the microstructure. Upon stress release at ~1 GPa/ns release rate, the reverse phase transition (hcp to bcc) to the original single crystal orientation (implying a transformation memory effect) was observed to reach completion somewhere between 13 and 11 GPa, indicating little stress hysteresis under rapid uniaxial strain release. A similar memory effect for the reverse hcp to bcc transformation has been previously observed under hydrostatic compression. However, the bcc/hcp orientation relationships differ somewhat between dynamic and static compression experiments, implying that the transformation pathway under uniaxial dynamic strain differs from the Burgers mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Controlled vapor crystal growth of N a 4 I r 3 O 8 : A three-dimensional quantum spin liquid candidate

In this work, we report the successful bulk single-crystal growth of the hyperkagome lattice iridate Na 4 Ir 3 O 8 (Na438) by vapor transport using a sealed aluminum oxide tube as a container. Crystals were characterized by magnetization, x-ray diffraction, and energy-dispersive x-ray measurements, confirming their identity and properties. Single-crystal x-ray diffraction experiments revealed superlattice peaks indexed on a propagation vector q=(1/3,1/3,1/3) based on the cubic substructure with cell parameter a=8.986(1)Å. This superlattice is three-dimensional and fully coherent. Polarization analysis rules out spin and/or orbital order as the underlying origin of the modulation and points to long-range ordering of Na ions at the notionally disordered Na sites as a plausible origin for the observed superlattice.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Measurement of shock roughness due to phase plate speckle imprinting relevant for x-ray diffraction experiments on 3rd and 4th generation light sources

Laser-shock compression experiments at 3rd and 4th generation light sources generally employ phase plates, which are inserted into the beamline to achieve a repeatable intensity distribution at the focal plane. Here, the laser intensity profile is characterized by a high-contrast, high-frequency laser speckle. Without sufficient smoothing, these laser non-uniformities can translate to a significant pressure distribution within the sample layer and can affect data interpretation in x-ray diffraction experiments. Here, we use a combination of one- and two-dimensional velocity interferometry to directly measure the extent to which spatial frequencies within the laser focal spot intensity pattern are smoothed out during propagation within the laser plasma and a polyimide ablator. We find that the use of thicker polyimide layers results in spatially smoother shock fronts, with the greatest degree of smoothing associated with the highest spatial frequencies. Focal spots with the smallest initial speckle separation produce the most rapid smoothing. Laser systems that employ smoothing by spectral dispersion techniques to rapidly modulate the focal plane intensity distribution are shown to be the most effective ones in producing a spatially smooth shock front. We show that a simple transport model combined with the known polyimide Hugoniot adequately describes the extent of shock smoothness as a function of polyimide thickness. Finally, our results provide a description of spatial structure smoothing across a shock front, which can be used to design targets on x-ray free electron laser facilities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Atomic layer epitaxy of kagome magnet Fe 3 Sn 2 and Sn-modulated heterostructures

Magnetic materials with kagome crystal structure exhibit rich physics, such as frustrated magnetism, skyrmion formation, topological flat bands, and Dirac/Weyl points. Until recently, most studies on kagome magnets have been performed on bulk crystals or polycrystalline films. Here, we report the atomic layer molecular beam epitaxy synthesis of high-quality thin films of topological kagome magnet Fe 3 Sn 2 . The structural and magnetic characterization of Fe 3 Sn 2 on epitaxial Pt(111) identifies highly ordered films with c-plane orientation and an in-plane magnetic easy axis. Studies on the local magnetic structure by anomalous Nernst effect imaging reveal in-plane oriented micrometer size domains. Superlattice structures consisting of Fe 3 Sn 2 and Fe 3 Sn are also synthesized by atomic layer molecular beam epitaxy, demonstrating the ability to modulate the sample structure at the atomic level. The realization of high-quality films by atomic layer molecular beam epitaxy opens the door to explore the rich physics of this system and investigate novel spintronic phenomena by interfacing Fe 3 Sn 2 with other materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Transition between Heavy-Fermion-Strange-Metal and Quantum Spin Liquid in a $4⁢d$-Electron Trimer Lattice

We present experimental evidence that a heavy Fermi surface consisting of itinerant, charge-neutral spinons underpins both heavy-fermion-strange-metal (without f electrons) and quantum-spin-liquid states in the 4d-electron trimer lattice, Ba 4 Nb 1-x Ru 3+x O 12 (|x| < 0.20). These two exotic states both exhibit an extraordinarily large entropy, a linear heat capacity extending into the milli-Kelvin regime, a linear thermal conductivity at low temperatures, and separation of charges and spins. Furthermore, the insulating spin liquid is a much better thermal conductor than the heavy-fermion-strange-metal that separately is observed to strongly violate the Wiedemann- Franz law. Here, we propose that at the heart of this 4d system is a universal, heavy spinon Fermi surface that provides a unified framework for explaining the exotic phenomena observed throughout the entire series. The control of such exotic ground states provided by variable Nb concentration offers a new paradigm for studies of correlated quantum matter.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Epitaxial growth, magnetoresistance, and electronic band structure of GdSb magnetic semimetal films

Motivated by observations of extreme magnetoresistance (XMR) in bulk crystals of rare-earth monopnictide (RE-V) compounds and emerging applications in novel spintronic and plasmonic devices based on thin-film semimetals, we have investigated the electronic band structure and transport behavior of epitaxial GdSb thin films grown on III-V semiconductor surfaces. The Gd 3 + ion in GdSb has a high spin S=7/2 and no orbital angular momentum, serving as a model system for studying the effects of antiferromagnetic order and strong exchange coupling on the resulting Fermi surface and magnetotransport properties of RE-Vs. Here, we present a surface and structural characterization study mapping the optimal synthesis window of thin epitaxial GdSb films grown on III-V lattice-matched buffer layers via molecular-beam epitaxy. To determine the factors limiting XMR in RE-V thin films and provide a benchmark for band-structure predictions of topological phases of RE-Vs, the electronic band structure of GdSb thin films is studied, comparing carrier densities extracted from magnetotransport, angle-resolved photoemission spectroscopy (ARPES), and density-functional theory (DFT) calculations. ARPES shows a hole-carrier rich, topologically trivial, semimetallic band structure close to complete electron-hole compensation, with quantum confinement effects in the thin films observed through the presence of quantum-well states. DFT-predicted Fermi wave vectors are in excellent agreement with values obtained from quantum oscillations observed in magnetic field-dependent resistivity measurements. An electron-rich Hall coefficient is measured despite the higher hole-carrier density, attributed to the higher electron Hall mobility. The carrier mobilities are limited by surface and interface scattering, resulting in lower magnetoresistance than that measured for bulk crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Conditional diffusion machine-learning framework for mapping valence electron distribution from convergent beam electron diffraction

Quantitative convergent beam electron diffraction (CBED) enables determination of aspherical valence electron distributions through refinement of low-order structure factors, which are highly sensitive to chemical bonding and charge density variations. However, conventional quantitative CBED (QCBED) requires solving a highly nonlinear inverse problem with many coupled parameters, and computationally intensive dynamical diffraction calculations, making it time-consuming and difficult to apply to complex systems. More broadly, reconstructing charge density and orbital electron distribution from diffraction data has long been a central challenge in both x-ray and electron crystallography. Here, in this study, we introduce an artificial-intelligence (AI)-based framework that replaces traditional refinement with a data-driven inverse solver. Using a large synthetic CBED dataset generated by Bloch-wave simulations, we train a conditional diffusion model to directly infer crystal structural parameters and multipole density formalism parameters, and hence valence electron distributions, from CBED patterns alone. By learning from forward simulations across realistic parameter space, the model effectively solves the inverse problem. Compared with direct regression approaches, the diffusion-based framework provides posterior parameter distributions for rigorous uncertainty quantification while preserving quantitative fidelity and reducing analysis time by orders of magnitude. By eliminating the need for external single-crystal x-ray diffraction data and complex nonlinear refinement, this approach enables practical, high-throughput, and in situ quantitative CBED, enabling real-time mapping of valence electron distributions and their correlation with functional responses in quantum and energy materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗