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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Isotropic parallel antiferromagnetism in the magnetic field induced charge-ordered state of $\mathrm{Sm Ru_4 P_{12}}$ caused by $p - f$ hybridization

Nature of the field-induced charge-ordered phase (phase II) of SmRu 4 P 12 has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the nonresonant Thomson scattering and the resonant magnetic scattering, combined with the spectral function obtained from x-ray magnetic circular dichroism, it is shown that the AFM moment of Sm prefers to be parallel to the field (m AF ∥ H), giving rise to large and small moment sites around which the P 12 and Ru cage contract and expand, respectively. This is associated with the formation of the staggered ordering of the Γ 7 -like and Γ 8 -like crystal-field states, providing a strong piece of evidence for the charge order. PND was also performed to obtain complementary and unambiguous conclusion. In addition, isotropic and continuous nature of phase II is demonstrated by the field-direction invariance of the interference spectrum in RXD. Finally, crucial role of the p-f hybridization is shown by resonant soft x-ray diffraction at the P K edge (1s↔3p), where we detected a resonance due to the spin polarized 3p orbitals reflecting the AFM order of Sm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Neutron diffraction: a primer

Because of the neutron’s special properties, neutron diffraction may be considered one of the most powerful techniques for structure determination of crystalline and related matter. Neutrons can be released from nuclear fission, from spallation processes, and also from low-energy nuclear reactions, and they can then be used in powder, time-of-flight, texture, single crystal, and other techniques, all of which are perfectly suited to clarify crystal and magnetic structures. With high neutron flux and sufficient brilliance, neutron diffraction also excels for diffuse scattering, for in situ and operando studies as well as for high-pressure experiments of today’s materials. For these, the wave-like neutron’s infinite advantage (isotope specific, magnetic) is crucial to answering important scientific questions, for example, on the structure and dynamics of light atoms in energy conversion and storage materials, magnetic matter, or protein structures. In this primer, we summarize the current state of neutron diffraction (and how it came to be), but also look at recent advances and new ideas, e.g., the design of new instruments, and what follows from that.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tuning the Radius Ratio to Enhance Thermoelectric Properties in the Zintl Compounds AM 2 Sb 2 (A = Ba, Sr; M = Zn, Cd)

Five novel Zintl phase solid solutions in the Ba 1–x Sr x Zn 2–y Cd y Sb 2 (0 ≤ x ≤ 0.13(1); 0 ≤ y ≤ 0.32(2)) system were successfully synthesized by the molten Pb metal-flux method, and the powder X-ray diffraction and single-crystal X-ray diffraction analyses proved that all five title compounds adopted the BaCu 2 S 2 -type phase having the orthorhombic Pnma space group (Z = 4, Pearson code oP20) with five crystallographically independent atomic sites. The previously studied BaCu 2 S 2 -type antimonides demonstrated a limited tolerance for doping in contrast to the CaAl 2 Si 2 -type antimonides. To understand the relatively narrower phase width and limited dopability of the title BaCu 2 S 2 -type phase than the CaAl 2 Si 2 -type phase in the overall Ba 1–x Sr x Zn 2–y Cd y Sb 2 system, the radius ratio of cations and anionic elements r + /r – for two structure types were thoroughly investigated. For the first time, the r + /r – ratio was identified as a critical factor for the phase selectivity: (1) r + /r – > 1 favored the BaCu 2 S 2 -type phase, and (2) r + /r – < 1 favored the CaAl 2 Si 2 -type phase. Further, we also revealed the structural transformation mechanism from the more widely observed CaAl 2 Si 2 -type phase to the title BaCu 2 S 2 -type phase as the relatively larger cationic elements were introduced to the system. A series of DFT calculations using the three hypothetical models indicated that a resonance peak near EF in the density of states curves was descended from the relatively flat band structure at several special symmetry points rationalizing the enhanced Seebeck coefficients of Ba 0.94(1) Sr 0.06 Zn 1.86(3) Cd 0.14 Sb 2 and Ba 0.96(1) Sr 0.04 Zn 1.68(2) Cd 0.32 Sb 2 . Electron localization function analysis rationalized the correlation between the polarity change of anionic Zn/Cd–Sb bonds and the charge carrier mobility on the anionic frameworks. Temperature-dependent thermoelectric properties were studied for the four title compounds, and the results proved that the Sr and Cd doping in the title Ba 1–x Sr x Zn 2–y Cd y Sb 2 system successfully enhanced the ZT values through the increased Seebeck coefficients and the reduced total thermal conductivities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Second Target Station (STS) Project: PIONEER Technical Report

PIONEER is a time-of-flight single-crystal neutron diffractometer at the Second Target Station (STS), aiming at providing the world-leading capability to measure tiny crystals (~0.001 mm 3 , i.e., X-ray diffraction size), ultra-thin epitaxial films (~10 nm thicknesses), and weak structural transitions and complex magnetism. The instrument will take advantage of STS source characteristics and utilize advancements in neutron optics to largely reduce the sample-volume requirement for single-crystal neutron diffraction. PIONEER will have a high-flux mode with multiple beam size options to improve the signal-to-background ratio in various sample environments. It will also provide a high Q-resolution mode by limiting beam divergence to study periodically modulated structures with characteristic lengths no less than 100 Å. Furthermore, it supports half-polarized neutron diffraction for investigating complex magnetism and local susceptibility. This report first overviews the proposed science case and the derived requirement. And then, the chosen technical solutions and expected performance will be described.

36 MATERIALS SCIENCE↗
DOE OSTI2026

The Modulated Crystal Structure of K 2 V 3 O 8

Weak lattice distortions can tune exchange pathways and magnetic interactions in square-lattice quantum magnets. K 2 V 3 O 8 is a mixed valence (V 4+ /V 5+ ) fresnoite oxide that exhibits strong spin–lattice coupling at low temperature. Here, we combine single-crystal neutron diffraction (90 K) and laboratory X-ray diffraction (50 K) to solve the low-temperature structure as an orthorhombic (3 + 1)D incommensurately modulated phase in superspace group Cmm2(β,0,1/2)0s0 [No. 196]. What initially appeared as two independent modulation vectors, q 1 = 0.3132(6)[$110$] + 1/2c* and q 2 = 0.3132(6)[$1\bar{10}$] + 1/2c*, are more naturally described as a single one-dimensional modulation wave q = 0.626(1)a* + 1/2c* in a C-centered orthorhombic lattice, related to the parent tetragonal cell by the transformation a + b, −a + b, c. Refinement with a 4-fold rotational twin inherited from the P4bm parent structure solves oxygen-dominated framework distortions and K + displacements. A de Wolff section (t = 0.40) enables a symmetry-mode decomposition, identifying three dominant mm2 (C 2v ) modes: GM3 for framework tilt, A5 for interlayer shear, and Z5 for c-axis breathing. The mode-resolved structure provides a unified, symmetry-based explanation for reported low-temperature Raman and IR anomalies and clarifies the structural origin of the spin–lattice coupling in the S = 1/2 two-dimensional quantum spin compound.

K2V3O8↗
DOE OSTI2026

Complex spin structure in co-trimer-chain Li 2 Co 3 Se 4 O 12

Complex magnetic materials are extremely attractive for revealing unconventional spin states and novel magnetic excitations. Here, we report the structural, thermodynamic, and magnetic properties of a novel magnetic material Li 2 Co 3 Se 4 O 12 based on x-ray and neutron diffraction, specific heat, magnetization, and x-ray photoelectron spectroscopy measurements. X-ray and neutron diffraction refinements reveal two Co sites Co (1) and Co (2) even though both are in the octahedral environment. While they are not connected along the b and c directions, these octahedra are edge-shared forming the Co (2) – Co (1) – Co (2) trimer chain along the a direction. The magnetic susceptibility exhibits the Curie-Weiss (CW) temperature dependence at high temperatures (above ∼50 K) with the negative CW temperature, a dip centered at T ⁎ ∼ 8.0 K, and an antiferromagnetic transition at T N = 3.3 K. The specific heat confirms that there is a phase transition at T N and a hump at T ⁎ . The long-range magnetic transition at T N implies that, in addition to the intra-chain interaction, there is strong inter-chain interaction, which is likely due to polarized SeO 3 bridging between chains. Single crystal neutron diffraction refinement reveals a complex magnetic structure with the angle between Co (1) and Co (2) moments ∼105°. Within the Co (2) – Co (1) – Co (2) trimer, two Co (2) moments are parallelly aligned. Surprisingly, the Co (1) moment (1.92μB) is only half of the Co (2) moment (3.96μB). There is likely the spin-state change for Co (1) from the high-spin state at T > T ⁎ to the low-spin state at T < T ⁎ , causing a dip in the magnetic susceptibility and a hump in the specific heat. When the magnetic field is applied, multiple metamagnetic transitions are found in all directions, implying field-driven magnetic excitations. Our results demonstrate rich magnetic properties of Li 2 Co 3 Se 4 O 12 that are sensitive to the external stimuli such as the magnetic field.

Antiferromagnetism↗
DOE OSTI2025

DXRD : a user-friendly suite of two- and multiple-beam dynamical X-ray diffraction programs

The DXRD program suite consisting of a series of dynamical theory programs is introduced for computing dynamical X-ray diffraction from single crystals. Its interactive graphical user interfaces (GUIs) allow general users to make complicated calculations with minimal effort. It can calculate plane-wave Darwin curves of single crystals (or multiple crystals) for both the Bragg and Laue cases, including grazing-incidence diffraction and backward diffraction (with Bragg angles approaching 90°). It is also capable of simulating rocking curves for divergent incident X-ray beams with finite bandwidths. A unique feature of DXRD is that it provides a convenient GUI-based multiple-beam diffraction program that can accurately compute arbitrary N-beam diffraction of any geometry using a universal 4N × 4N matrix method. DXRD also provides a mapping program for plotting all the multiple-beam diffraction lines (monochromator glitches) in the azimuth–energy coordinate system. All these functions make DXRD a convenient and powerful software tool for designing crystal-based synchrotron/X-ray optics (monochromators, analyzers, polarizers, phase plates etc.) and for crystal characterization, X-ray spectroscopy and X-ray diffraction teaching.

Bragg reflection↗
DOE OSTI2024

Magnetic properties of the quasi-XY Shastry-Sutherland magnet ER 2 Be 2 SiO 7

Polycrystalline and single-crystal samples of the insulating Shastry-Sutherland compound Er 2 ⁢Be 2 ⁢SiO 7 were synthesized via a solid-state reaction and the floating zone method, respectively. The crystal structure, Er single-ion anisotropy, zero-field magnetic ground state, and magnetic phase diagrams along high-symmetry crystallographic directions were investigated with bulk measurement techniques, x-ray and neutron diffraction, and neutron spectroscopy. Here, we establish that Er 2 ⁢Be 2 ⁢SiO 7 crystallizes in a tetragonal space group with planes of orthogonal Er dimers and a strong preference for the Er moments to lie in the local plane perpendicular to each dimer bond. We also find that this system has a noncollinear ordered ground state in zero field with a transition temperature of 0.841 K consisting of antiferromagnetic dimers and in-plane moments. Finally, we mapped out the H-T phase diagrams for Er 2 ⁢Be 2 ⁢SiO 7 along the directions H ∥ [001], [100], and [110]. While an increasing in-plane field simply induces a phase transition to a field-polarized phase, we identify three metamagnetic transitions in the H ∥ [001] case. Single-crystal neutron diffraction results reveal that the H ∥ [001] phase diagram can be explained predominantly by the expected field-induced behavior of classical, anisotropic moments, although the microscopic origin of one phase requires further investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Physical properties and anisotropic magnetism of EuBi 2

We report the synthesis of EuBi 2 single crystals and their magnetic and electronic properties. Plate-like crystals were grown in excess bismuth, and X-ray diffraction data confirm the previously reported tetragonal space group, I 4 1 /amd (No. 141). A Néel temperature of T N = 18.6 K was determined from the specific heat data, and corresponding anomalies occur in the magnetization and resistivity. We only observe one magnetic transition in zero magnetic field. The magnetization data above 70 K are well described by a Curie-Weiss model with a Weiss temperature of Θ CW ≈ −35 K and an effective moment near that of the expected spin-only moment of Eu 2+ (S = 7/2). Isothermal magnetization measurements reveal field-induced transitions for H||[100], including a hysteretic spin-flop centered at 10.1 T and a change in slope at 12 T and 2 K. However, while the isothermal magnetization for H||[110] displays nonlinear behavior, discrete metamagnetic transitions are not observed for H||[110] or H||[001], indicating significant magnetic anisotropy. The magnetization does not saturate by 13.5 T for any orientation. EuBi 2 is metallic and our crystals possess an in-plane residual resistivity ratio of ⍴300 K/⍴2 K ≈ 40. Single crystal neutron diffraction data reveal a large magnetic unit cell and non-trivial antiferromagnetic ordering. These results demonstrate that strong antiferromagnetic coupling drives complex magnetism in EuBi 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2026

Framework Short-Range Order Observed in a Spinel-Type Li Superionic Conductor

Solid-state superionic conductors are characterized by rich structural disorders. Though structural complexities are central to their functionalities, they often give rise to short-range order that eludes detection by conventional diffraction-based techniques and is thus overlooked in establishing precise structure-property relationships. In this work, we synthesized single crystals of a recently discovered lithium (Li) superionic conductor Li16.2(1)In9.00(2)Sn1.10(1)O23.8 (LISO) for in-depth characterizations of structural subtleties. LISO exhibits an unusual spinel-like phase with significant Li overstoichiometry and a face-sharing Li network. Single-crystal neutron diffraction confirms significant Li disorder, as manifested in Li site splitting and partial occupancy. More importantly, synchrotron diffuse scattering combined with 3D-ΔPDF analysis and Monte Carlo simulations reveal short-range order in the nonalkali framework that might contribute to the phase stability and ionic conductivity. This work showcases an example in which subtle local energetics can be directly visualized in structurally disordered ionic conductors.

Chen, Yu↗
DOE OSTI2024

Electric-Field Manipulation of Magnetic Chirality in a Homo-Ferro-Rotational Helimagnet

Ferro-rotational (FR) materials, renowned for their distinctive material functionalities, present challenges in the growth of homo-FR crystals (i.e., single FR domain). This study explores a cost-effective approach to growing homo-FR helimagnetic RbFe(SO 4 ) 2 (RFSO) crystals by lowering the crystal growth temperature below the T FR threshold using the high-pressure hydrothermal method. Through polarized neutron diffraction experiments, it is observed that nearly 86% of RFSO crystals consist of a homo-FR domain. Notably, RFSO displays remarkable stability in the FR phase, with an exceptionally high T FR of ≈573 K. Furthermore, RFSO exhibits a chiral helical magnetic structure with switchable ferroelectric polarization below 4 K. Importantly, external electric fields can induce a single magnetic domain state and manipulate its magnetic chirality. The findings suggest that the search for new FR magnets with outstanding material properties should consider magnetic sulfates as promising candidates.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Multifunctional Cu 2 TSiS 4 (T = Mn and Fe): Polar Semiconducting Antiferromagnets with Nonlinear Optical Properties

In this work, Cu 2 TSiS 4 (T = Mn and Fe) polycrystalline and single-crystal materials were prepared with high-temperature solid-state and chemical vapor transport methods, respectively. The polar crystal structure (space group Pmn2 1 ) consists of chains of corner-sharing and distorted CuS 4 , Mn/FeS 4 , and SiS 4 tetrahedra, which is confirmed by Rietveld refinement using neutron powder diffraction data, X-ray single-crystal refinement, electron diffraction, energy-dispersive X-ray spectroscopy, and second harmonic generation (SHG) techniques. Magnetic measurements indicate that both compounds order antiferromagnetically at 8 and 14 K, respectively, which is supported by the temperature-dependent (100–2 K) neutron powder diffraction data. Additional magnetic reflections observed at 2 K can be modeled by magnetic propagation vectors k = (1/2,0,1/2) and k = (1/2,1/2,1/2) for Cu 2 MnSiS 4 and Cu 2 FeSiS 4 , respectively. The refined antiferromagnetic structure reveals that the Mn/Fe spins are canted away from the ac plane by about 14°, with the total magnetic moments of Mn and Fe being 4.1(1) and 2.9(1) μ B , respectively. Both compounds exhibit an SHG response with relatively modest second-order nonlinear susceptibilities. Density functional theory calculations are used to describe the electronic band structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Chemical crystallography by serial femtosecond X-ray diffraction

Abstract Inorganic–organic hybrid materials represent a large share of newly reported structures, owing to their simple synthetic routes and customizable properties 1 . This proliferation has led to a characterization bottleneck: many hybrid materials are obligate microcrystals with low symmetry and severe radiation sensitivity, interfering with the standard techniques of single-crystal X-ray diffraction 2,3 and electron microdiffraction 4–11 . Here we demonstrate small-molecule serial femtosecond X-ray crystallography (smSFX) for the determination of material crystal structures from microcrystals. We subjected microcrystalline suspensions to X-ray free-electron laser radiation 12,13 and obtained thousands of randomly oriented diffraction patterns. We determined unit cells by aggregating spot-finding results into high-resolution powder diffractograms. After indexing the sparse serial patterns by a graph theory approach 14 , the resulting datasets can be solved and refined using standard tools for single-crystal diffraction data 15–17 . We describe the ab initio structure solutions of mithrene (AgSePh) 18–20 , thiorene (AgSPh) and tethrene (AgTePh), of which the latter two were previously unknown structures. In thiorene, we identify a geometric change in the silver–silver bonding network that is linked to its divergent optoelectronic properties 20 . We demonstrate that smSFX can be applied as a general technique for structure determination of beam-sensitive microcrystalline materials at near-ambient temperature and pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

An Atomic View of Cation Diffusion Pathways from Single‐Crystal Topochemical Transformations

Abstract The diffusion pathways of Li‐ions as they traverse cathode structures in the course of insertion reactions underpin many questions fundamental to the functionality of Li‐ion batteries. Much current knowledge derives from computational models or the imaging of lithiation behavior at larger length scales; however, it remains difficult to experimentally image Li‐ion diffusion at the atomistic level. Here, by using topochemical Li‐ion insertion and extraction to induce single‐crystal‐to‐single‐crystal transformations in a tunnel‐structured V 2 O 5 polymorph, coupled with operando powder X‐ray diffraction, we leverage single‐crystal X‐ray diffraction to identify the sequence of lattice interstitial sites preferred by Li‐ions to high depths of discharge, and use electron density maps to create a snapshot of ion diffusion in a metastable phase. Our methods enable the atomistic imaging of Li‐ions in this cathode material in kinetic states and provide an experimentally validated angstrom‐level 3D picture of atomic pathways thus far only conjectured through DFT calculations.

Handy, Joseph V.↗
DOE OSTI2021

Self-similar mesocrystals form via interface-driven nucleation and assembly

Crystallization by particle attachment (CPA) is a frequently occurring mechanism of colloidal crystallization that results in hierarchical morphologies. CPA has been exploited to create nanomaterials with unusual properties and is implicated in the development of complex mineral textures. Oriented attachment–a form of CPA in which particles align along specific crystallographic directions–produces mesocrystals that diffract as single crystals do, although the constituent particles are still discernible. The conventional view of CPA is that nucleation provides a supply of particles that aggregate via Brownian motion biased by attractive interparticle potentials. However, mesocrystals often exhibit regular morphologies and uniform sizes. Although many crystal systems form mesocrystals and individual attachment events have been directly visualized10, how random attachment events lead to well defined, self-similar morphologies remains unknown, as does the role of surface-bound ligands, which are ubiquitous in nanoparticle systems. Attempts to understand mesocrystal formation are further complicated in many systems by the presence of precursor nanoparticles with a phase distinct from that of the bulk. Some studies propose that such particles convert before attachment, whereas others attribute conversion to the attachment process itself and yet others conclude that transformation occurs after the mesocrystals exceed a characteristic size. Here we investigate mesocrystal formation by iron oxides, which are important colloidal phases in natural environments and classic examples of systems forming ubiquitous precursor phases and undergoing CPA accompanied by phase transformations. Combining in situ transmission electron microscopy (TEM) at 80 degrees Celsius with ‘freeze-and-look’ TEM, we tracked the formation of haematite (Hm) mesocrystals in the presence of oxalate (Ox), which is abundant in soils, where iron oxides are common. In this work, we find that isolated Hm particles rarely appear, but once formed, interfacial gradients at the Ox-covered surfaces drive Hm particles to nucleate repeatedly about two nanometres from the surfaces, to which they then attach, thereby generating mesocrystals. Comparison to natural and synthetic systems suggests that interface-driven pathways are widespread.

36 MATERIALS SCIENCE↗
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↗