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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Final Technical Report on Investigation of Short-range Ordering in Transition Metal Compounds by Diffuse Scattering

Future energy needs and sustainability require new materials with novel properties for such applications as energy production, storage and transport and microelectronics. Quantum materials with several competing interactions at the electronic level offer tremendous opportunity to discover, design and tune properties for such applications. Although it has been recognized that small deviations in atomic positions, driven by the competing electronic interactions, in crystalline materials can have significant impact on properties, it remains a challenge to accurately characterize such deviations (short-range order) due to the lack of advanced instruments and analysis tools to characterize them. This project used the powerful neutron and x-ray scattering instruments recently developed at the DOE user facilities to address this challenge. New methods and efficient analysis tools were employed to uncover the hidden ordering that is behind the unique properties of transition metal compounds. One example of hidden order revealed by this project comes from vanadium (IV) oxide (VO 2 ) and related compounds. The project found that the chemical bonds in VO 2 compete against each other, unlike most crystalline compounds where the chemical bonds cooperate to yield the ordered structure. This helps explain why different measurements yielded different, competing pictures about the nature of VO 2 , which has led to disagreement about where its physical properties come from. Another example from this project of hidden ordering comes from a class of compounds known as condensed Chevrel phases, which are superconducting compounds that are generally believed to be non-magnetic. The neutron scattering methods used in this project revealed evidence of magnetism, which usually does not coexist with superconductivity. In this case, magnetism is believed to be one part of a special type of electronic behavior that can occur in compounds that have one-dimensional bonding character.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanoscale structure in AgSbTe2 determined by diffuse elastic neutron scattering

Diffuse elastic neutron scattering measurements confirm that AgSbTe2 has a hierarchical structure, with defects on length scales from nanometers to microns. While scattering from mesoscale structure is consistent with previously-proposed structures in which Ag and Sb order on a NaCl lattice, more diffuse scattering from nanoscale structure suggests a structural rearrangement in which hexagonal layers form a combination of (ABC), (ABA), and (AAB) stacking sequences. The AgCrSe2 structure is the best-fitting model for the local atomic arrangements.

Specht, Eliot D↗
DOE OSTI2015

Inter-atomic force constants of BaF{sub 2} by diffuse neutron scattering measurement

Diffuse neutron scattering measurement on BaF{sub 2} crystals was performed at 10 K and 295 K. Oscillatory form in the diffuse scattering intensity of BaF{sub 2} was observed at 295 K. The correlation effects among thermal displacements of F-F atoms were obtained from the analysis of oscillatory diffuse scattering intensity. The force constants among neighboring atoms in BaF{sub 2} were determined and compared to those in ionic crystals and semiconductors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Persistent low-energy phonon broadening near the charge-order q vector in the bilayer cuprate Bi 2 Sr 2 CaCu 2 O 8 + δ

Here, we report a persistent low-energy phonon broadening around q B ~ 0.28 reciprocal lattice unit (r.l.u.) along the Cu-O bond direction in the high- T c cuprate Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212). We show that such broadening exists both inside and outside the conventional charge-density wave (CDW) phase, via temperature-dependent measurements in both underdoped and heavily overdoped samples. Combining inelastic hard x-ray scattering, diffuse scattering, angle-resolved photoemission spectroscopy, and resonant soft x-ray scattering at the Cu L 3 -edge, we exclude the presence of a CDW in the heavily overdoped Bi-2212 similar to that observed in the underdoped systems. Finally, we discuss the origin of such anisotropic low-energy phonon broadening and its potential precursory role to the CDW phase in the underdoped region.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cepstral scanning transmission electron microscopy imaging of severe lattice distortions

The development of four-dimensional (4D) scanning transmission electron microscopy (STEM) using fast detectors has opened-up new avenues for addressing some of longstanding challenges in electron imaging. One of these challenges is how to image severely distorted crystal lattices, such as at a dislocation core. Here we develop a new 4D-STEM technique, called Cepstral STEM, for imaging disordered crystals using electron diffuse scattering. In contrast to analysis based on Bragg diffraction, which measures the average and periodic scattering potential, electron diffuse scattering can detect fluctuations caused by crystal disorder. Local fluctuations of diffuse scattering are captured by scanning electron nanodiffraction (SEND) using a coherent probe. The harmonic signals in electron diffuse scattering are detected through Cepstral analysis and used for imaging. By integrating Cepstral analysis with 4D-STEM, we demonstrate that information about the distortive part of electron scattering potential can be separated and imaged at nm spatial resolution. Here, we apply the technique to the analysis of a dislocation core in SiGe and lattice distortions in a high entropy alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Lead-free and lead-based ABO3 perovskite relaxors with mixed-valence A-site and B-site disorder: A comparative neutron scattering structural study of (Na1/2Bi1/2)TiO3 and Pb(Mg1/3Nb2/3)O3

We report the results of neutron elastic scattering measurements between -250oC and 620oC on the lead-free relaxor Na1/2Bi1/2TiO3 (NBT). Strong, anisotropic, elastic diffuse scattering intensity decorates the (100), (110), (111), (200), (220), and (210) Bragg peaks at room temperature. The wavevector dependence of this diffuse scattering is compared to that in the lead-based relaxor PbMg1/3Nb2/3O3 (PMN) to determine if any features might be common to relaxors. Prominent ridges in the elastic diffuse scattering intensity contours that extend along <110> are seen that exhibit the same zone dependence as those observed in PMN and other lead-based relaxors. These ridges disappear gradually on heating above the cubic-to-tetragonal phase transition temperature TCT = 523oC, which is also near the temperature at which the dielectric permittivity begins to deviate from Curie-Weiss behavior. We thus identify the <110>-oriented ridges as a relaxor-specific property. The diffuse scattering contours also display narrower ridges oriented along <100> that are consistent with the x-ray results of Kreisel et al. (2003); these vanish below 320oC indicating that they have a different physical origin. The <100>-oriented ridges are not observed in PMN. We observe no equivalent relaxor-specific elastic diffuse scattering from the homovalent relaxor analogues K0.95Li0.05TiO3 (A-site disordered) and KTa0.95Nb0.05O3 (B-site disordered). This suggests that the <110>-oriented diffuse scattering ridges are correlated with the presence of strong random electric fields and invites a reassessment of what defines the relaxor phase. We find that doping NBT with 5.6% BaTiO3, a composition close to the morphotropic phase boundary with enhanced piezoelectric properties, increases the room temperature correlation length along [1 1 0] from 40 to 60 while doubling the associated integrated diffuse scattering. Similar behavior was reported by Matsuura et al. (2006) for compositions of PMN doped with PbTiO3. Finally, we comment on the recent observation of monoclinicity in NBT at room temperature by placing a strict bound on the strength of the ( ) superlattice reflection associated with the Cc space group based on the atomic coordinates published in the x-ray study by Aksel et al. (2011) for NBT. We argue that a skin effect, analogous to that reported in the relaxors PZN and PMN-10%PT, can reconcile our single-crystal data with the powder data of Aksel et al. We believe this represents the first evidence of the relaxor skin effect in a lead-free relaxor.

Ge, Wenwei↗
DOE OSTI2024

Reconstructing the reflectivity of liquid surfaces from grazing incidence X-ray off-specular scattering data

The capillary wave model of a liquid surface predicts both the X-ray specular reflection and the diffuse scattering around it. A quantitative method is presented to obtain the X-ray reflectivity (XRR) from a liquid surface through the diffuse scattering data around the specular reflection measured using a grazing incidence X-ray off-specular scattering (GIXOS) geometry at a fixed horizontal offset angle with respect to the plane of incidence. With this approach the entire Q z -dependent reflectivity profile can be obtained at a single, fixed incident angle. This permits a much faster acquisition of the profile than with conventional reflectometry, where the incident angle must be scanned point by point to obtain a Q z -dependent profile. The XRR derived from the GIXOS-measured diffuse scattering, referred to in this paper as pseudo-reflectivity, provides a larger Q z range compared with the reflectivity measured by conventional reflectometry. Transforming the GIXOS-measured diffuse scattering profile to pseudo-XRR opens up the GIXOS method to widely available specular XRR analysis software tools. Here the GIXOS-derived pseudo-XRR is compared with the XRR measured by specular reflectometry from two simple vapor–liquid interfaces at different surface tension, and from a hexadecyltrimethylammonium bromide monolayer on a water surface. For the simple liquids, excellent agreement (beyond 11 orders of magnitude in signal) is found between the two methods, supporting the approach of using GIXOS-measured diffuse scattering to derive reflectivities. Pseudo-XRR obtained at different horizontal offset angles with respect to the plane of incidence yields indistinguishable results, and this supports the robustness of the GIXOS-XRR approach. The pseudo-XRR method can be extended to soft thin films on a liquid surface, and criteria are established for the applicability of the approach.

36 MATERIALS SCIENCE↗
DOE OSTI2025

In-Plane Anisotropy of Charge Density Wave Fluctuations in 1⁢𝑇−TiSe 2

We report measurements of anisotropic triple-𝑞 charge density wave (CDW) fluctuations in the transition metal dichalcogenide 1⁢𝑇−TiSe 2 over a large volume of reciprocal space with x-ray diffuse scattering. Above the transition temperature, 𝑇 CDW , the in-plane diffuse scattering is marked by ellipses which reveal that the in-plane fluctuations are anisotropic. In addition, the out-of-plane diffuse scattering is characterized by rodlike structures which indicate that the CDW fluctuations in neighboring layers are largely decoupled. Furthermore, our analysis of the diffuse scattering line shapes and orientations suggests that the three charge density wave components contain independent phase fluctuations with a hierarchy of length scales, leading to intricate fluctuation patterns that go beyond the conventional 2D-to-3D crossover picture.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Direct evidence of correlations between relaxor behavior and polar nano-regions in relaxor ferroelectrics: A case study of lead-free piezoelectrics Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}-x%BaTiO{sub 3}

Diffuse scattering and relaxor behavior in Na{sub 0.5}Bi{sub 0.5}TiO{sub 3} (NBT) and NBT-5.6 at. %BaTiO{sub 3} (NBT-5.6%BT) were investigated. X-ray diffraction revealed two types of diffuse scattering in NBT: (i) broad and (ii) asymmetric L-shaped. After modification with 5.6%BT, the broad diffuse scattering patterns became narrow, and the asymmetric L-shaped ones were replaced by symmetric ones. The symmetric diffuse scattering in NBT-5.6%BT disappeared with increasing dc electric field (E) for E ≥ 9.5 kV/cm where the frequency dispersion in the dielectric constant disappeared. These results demonstrate that the relaxor characteristics are directly correlated with the diffuse scattering and the presence polar nano-regions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Epitaxial intergrowths and local oxide relaxations in natural bixbyite Fe 2– x Mn x O 3

The scattering pattern of a crystal obeys the symmetry of the crystal structure through the corresponding Laue group. This is usually also true for the diffuse scattering, containing information about disorder, but here a case is reported where the diffuse scattering is of lower symmetry than the parent crystal structure. The mineral bixbyite has been studied by X-ray and neutron scattering techniques since 1928 with some of the most recent studies characterizing the low-temperature transition to a magnetically disordered spin-glass state. However, bixbyite also exhibits structural disorder, and here single-crystal X-ray and neutron scattering is used to characterize the different modes of disorder present. One-dimensional rods of diffuse scattering are observed in the cubic mineral bixbyite, which break the expected symmetry of the scattering pattern. It is shown that this scattering arises from epitaxial intergrowths of the related mineral, braunite. The presence of this disorder mode is found to be directly observable as well-defined residuals in the average structure refined against the Bragg diffraction. An additional three-dimensional diffuse scattering component is observed in neutron scattering data, which is shown to originate from the substitutional disorder on the Fe/Mn sites. This occupational disorder gives rise to local relaxations of the oxide sublattice, and the pattern of oxide displacements can be rationalized based on crystal-field theory. The combined use of neutron and X-ray single-crystal scattering techniques highlights their great complementarity. In particular, the large sample requirements for neutron scattering experiments prove to be an obstacle in solving the intergrowth disorder due to several growth orientations, whereas for X-ray scattering the one-dimensional nature of the intergrowth disorder renders solving this a more tractable task. On the other hand, the oxide relaxations cannot be resolved using X-rays due to the low Mn/Fe contrast. By combining the two approaches both types of disorder have been characterized.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Single-Crystal Diffuse Neutron Scattering Study of the Dipole-Octupole Quantum Spin-Ice Candidate Ce 2⁢ Zr 2 ⁢O 7 : No Apparent Octupolar Correlations Above 𝑇 = 0.05 K

The insulating magnetic pyrochlore Ce 2 ⁢Zr 2 ⁢O 7 has gained attention as a quantum spin-ice candidate with dipole-octupole character that arises from the crystal-electric-field ground-state doublet for the Ce 3+ Kramers ion. This dipole-octupole character permits both spin-ice phases based on magnetic dipoles and those based on more-exotic octupoles. This work reports low-temperature neutron diffraction measurements on single-crystal Ce 2 ⁢Zr 2⁢ O 7 with 𝑄 coverage both at low 𝑄, where the magnetic form factor for dipoles is near maximal, and at high 𝑄, covering the region where the magnetic form factor for Ce 3+ octupoles is near maximal. This study was motivated by recent powder neutron diffraction studies of other Ce-based dipole-octupole pyrochlores, Ce 2 ⁢Sn 2 ⁢O 7 and Ce 2 ⁢Hf 2 ⁢O 7 , which each showed temperature-dependent diffuse diffraction at high 𝑄, interpreted as arising from octupolar correlations. Our measurements use an optimized single-crystal diffuse scattering instrument that allows us to screen against strong Bragg scattering from Ce 2 ⁢Zr 2 ⁢O 7 . The temperature-difference neutron diffraction reveals a low-𝑄 peak consistent with dipolar spin-ice correlations reported in previous work, and an alternation between positive and negative net intensity at higher 𝑄. These features are consistent with our numerical-linked-cluster calculations using pseudospin interaction parameters previously reported for Ce 2 ⁢Zr 2⁢ O 7 , Ce 2 ⁢Sn 2 ⁢O 7 , and Ce 2 ⁢Hf 2 ⁢O 7 . Importantly, neither the measured data nor any of the NLC calculations show evidence for increased scattering at high 𝑄 resulting from octupolar correlations. We conclude that at the lowest attainable temperature for our measurements (𝑇 = 0.05 K), scattering from octupolar correlations in Ce 2 ⁢Zr 2 ⁢O 7 is not present in the neutron diffraction signal on the level of our observation threshold of around 0.1% of the low-𝑄 dipole scattering. We compare these results to those obtained earlier on powder Ce 2 ⁢Sn 2 ⁢O 7 and Ce 2⁢ Hf 2⁢ O 7 , and to low-energy inelastic neutron scattering from single-crystal Ce 2 ⁢Zr 2 ⁢O 7 .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fermi-surface driven frustrations in charge ordered kagome metal LuNb 6 ⁢Sn 6

The charge density wave (CDW), a translational symmetry breaking electronic liquid, plays a pivotal role in correlated quantum materials, such as high-𝑇 𝑐 superconductors and topological semimetals. Recently, CDWs that possibly intertwine with superconductivity and magnetism are observed in various kagome metals. However, the nature of CDWs and the role of the Fermi-surface (FS) topology in these materials remain an unresolved challenge. In this paper, we reveal the formation of CDWs in the newly discovered kagome metal LuNb 6 ⁢Sn 6 . Here, we observe a ‘‘yield sign’’-like hollow triangular diffuse scattering pattern and nearly complete softening of a flat optical phonon band near 𝐐 𝐻 = (1/3,1/3,1/2). The scattering intensity of the diffuse scattering displays divergent behavior as decreasing temperature until 𝑇 CDW = 70 K, where a competing CDW at 𝑄 CDW = (1/3,1/3,1/3) emerges. Combined with scanning tunneling microscopy/spectroscopy and first-principles calculations, our observations support a Fermi-surface driven frustration that suppresses the leading CDW instability at 𝐐 𝐻 . This frustration is relieved by the emergence of a subleading CDW at 𝑄 CDW . These results provide insights into the interplay between the Fermi surface, strong electron-phonon coupling, and charge density wave formation in quantum materials.

Yang, F. Z. [Oak Ridge National Laboratory (ORNL),↗