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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

3d Crystallographic Orientation of Olivine in Bjurböle Chondrules

The crystallographic orientations of chondrule minerals can provide important insights into their formation and deformational history. For example, the orientations of the olivine bars and surrounding rim in barred olivine chondrules provide information and on the conditions of crystallization and the orientations and shapes of olivines within porphritic chondrules can record the reactions with the surrounding nebular gas during chondrule formation. Later deformation on the parent body can cause crystal-plastic deformation of chondrule minerals that is evident through their intracrystalline lattice misorientations. Typically these crystal orientations and lattice misorientations are determined using electron backscatter diffraction (EBSD) on thin sections but this gives only a 2D picture for what is actually a 3D texture. While it is possible to combine EBSD with serial sectioning to build a 3D dataset of texture, this is a destructive, time-intensive process. A recent technological development that enables non-destructive, 3D crystallographic orientation measurement is X-ray diffraction contrast tomography (DCT), which uses the X-ray diffraction of the crystal lattice to determine orientation. Originally only possible using monochromatic X-ray beams at 3rd generation synchrotron light sources, DCT has been recently adapted to polychromatic sources of laboratory X-ray microscopes (referred to as Lab-DCT). Up to this point LabDCT has only been applied to large, well-formed crystals of high symmetry (i.e., metals), but we recently acquired DCT datasets for a pair Bjurböle chondrules to determine the applicability of the technique to natural, mutlimineralic samples composed predominately of olivine (i.e., chondrules).

Hanna, R. D.↗
DOE OSTI2024

Systems and methods for disassembling two-dimensional van der Waals crystals into macroscopic monolayers and reassembling into artificial lattices

Systems and methods for generating one or more single crystal monolayers from two-dimensional van der Waals crystals are disclosed herein. Example methods include providing a bulk material including a plurality of van der Waals crystal layers, and exfoliating one or more single crystal monolayers of van der Waals crystal from the bulk material by applying a flexible and flat metal tape to a surface of the bulk material. In certain embodiments, the one or more single crystal monolayers can be assembled into an artificial lattice. The present disclosure also provides techniques for manufacturing flexible and flat metal tape for generating one or more single crystal monolayers from two-dimensional van der Waals crystals. The present disclosure also provides compositions for creating a macroscopic artificial lattice. In certain embodiments, the composition can include two or more macroscopic single crystal monolayers adapted from a bulk van der Waals crystal, where the single crystal monolayers are configured for assembly into an artificial lattice based on one or more properties.

Source record↗
DOE OSTI2020

Commensurate states and pattern switching via liquid crystal skyrmions trapped in a square lattice

Using continuum based simulations we show that a rich variety of skyrmion liquid crystal states can be realized in the presence of a periodic obstacle array. As a function of the number of skyrmions per obstacle we find hexagonal, square, dimer, trimer and quadrimer ordering, where the n-mer structures are a realization of a molecular crystal state of skyrmions. As a function of external field and obstacle radius we show that there are transitions between the different crystalline states as well as mixed and disordered structures. Here, we discuss how these states are related to commensurate effects seen in other systems, such as vortices in type-II superconductors and colloids interacting with two dimensional substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Development of “GaSb-on-silicon” metamorphic substrates for optoelectronic device growth

The epitaxial development and characterization of metamorphic “GaSb-on-silicon” buffers as substrates for antimonide devices is presented. The approach involves the growth of a spontaneously and fully relaxed GaSb metamorphic buffer in a primary epitaxial reactor, and use of the resulting “GaSb-on-silicon” wafer to grow subsequent layers in a secondary epitaxial reactor. The buffer growth involves four steps—silicon substrate preparation for oxide removal, nucleation of AlSb on silicon, growth of the GaSb buffer, and finally capping of the buffer to prevent oxidation. This approach on miscut silicon substrates leads to a buffer with negligible antiphase domain density. The growth of this buffer is based on inducing interfacial misfit dislocations between an AlSb nucleation layer and the underlying silicon substrate, which results in a fully relaxed GaSb buffer. A 1 μm thick GaSb layer buffer grown on silicon has ~9.2 × 10 7 dislocations/cm 2 . The complete lack of strain in the epitaxial structure allows subsequent growths to be accurately lattice matched, thus making the approach ideal for use as a substrate. Here we characterize the GaSb-on-silicon wafer using high-resolution x-ray diffraction and transmission electron microscopy. The concept’s feasibility is demonstrated by growing interband cascade light emitting devices on the GaSb-on-silicon wafer. The performance of the resulting LEDs on silicon approaches that of counterparts grown lattice matched on GaSb.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Crystal plasticity finite element simulation of lattice rotation and x-ray diffraction during laser shock compression of tantalum

Here we present a crystal plasticity model tailored for high-pressure, high-strain-rate conditions that uses a multiscale treatment of dislocation-based slip kinetics. We use this model to analyze the pronounced plasticity-induced lattice rotations observed in shock-compressed polycrystalline tantalum via in situ x-ray diffraction. By making direct comparisons between experimentally measured and simulated texture evolution, we can explain how the details of the underlying slip kinetics control the degree of lattice rotation that ensues. Specifically, we show that only the highly nonlinear kinetics caused by dislocation nucleation can explain the magnitude of the rotation observed under shock compression. We demonstrate a good fit between our crystal plasticity model and x-ray diffraction data and exploit the data to quantify the dislocation nucleation rates that are otherwise poorly constrained by experiment in the dynamic compression regime.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A microscopic perspective on moiré materials

Quantum materials research has experienced a veritable renaissance in the past 6 years, with a surge of experimental reports of nearly every known electronic phase of matter and of several unique and unexpected phases, all found in an emerging class of highly tunable 2D materials, known as moiré materials1,2,3. Here, moiré materials are designed through either the rotational misalignment of identical 2D atomic crystals or the lattice mismatch of dissimilar 2D atomic crystals (Fig. 1). Both these incommensurability conditions cause long-wavelength (~10 nm) interference patterns between the two constituent atomic lattices, forming an enlarged moiré superlattice that generically hosts flat electronic bands, which are highly conducive to correlated, collective phases of matter.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Triel-Defined Helicity in One-Dimensional III–VI–VII van der Waals Crystals

Inorganic extended lattice solids that bear complex helical motifs manifest unusual physical and quantum states that arise due to their noncentrosymmetric or chiral nature. However, the systematic understanding of how elemental composition influences the structure and physical properties in helical inorganic crystals has been precluded by the rarity of these materials and the lack of modular phases that display such motifs. Here, we report the synthesis of AlSeI single crystals, the first aluminum-containing helical crystal in the III-VI-VII 1D van der Waals class. AlSeI completes the experimentally accessible triel series in the helical selene iodides alongside InSeI and GaSeI. Using the Al, Ga, and In triel series in this selene iodide class, we experimentally demonstrate the evolution of the local quasi-tetrahedral building unit geometry, chain packing, helical parameters, and band gaps based primarily on the identity of the triel atom. Our results underscore the chemical modularity of these phases, the broad range of helical parameters, and the spectrum of electronic states from the visible to the ultraviolet range in this emergent class of 1D, exfoliable, and helical extended lattice solids.

Chemical structure↗
DOE OSTI2021

From crystal color symmetry to quantum spacetime

More than one hundred years after the inception of relativistic physics, the concept of time remains incompletely understood. Relativity provides means to perform calculations of geometrical properties of spacetime, such as distances or curvature, and to interpret them in terms of physical observations, for instance as time dilation or gravitational effects. However, an intuitive understanding of spacetime is complicated, not so much because it is four-dimensional (which, after all, can be evaded by visualizing twodimensional cross sections) but mainly because its geometry does not obey Euclid’s axioms even in the absence of curvature. Through a well defined and clever transformation (RBS: renormalized blended spacetime), Venkatraman Gopalan (2021) has demonstrated how the hyperbolic geometry in Minkowski spacetime can be mapped to a circular Euclidean geometry. In particular, Lorentzian boosts become Euclidean rotations which enables new frontiers of exploration in color symmetry and magnetic crystals. His idea of general relativistic spacetime crystals and how to obtain them is both powerful and broad, although the notion of relativistic crystals and lattices in two dimensions has existed for a while (Janner & Ascher, 1969a,b). Finally, the breadth of this new work is underlined by the present opinion piece, written by two co-authors with distinct yet connected areas of expertise.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Coexistence of commensurate and incommensurate antiferromagnetic ground states in Co 𝑥 ⁢NbSe 2 single crystal

In Co 𝑥 ⁢NbSe 2 , crystal symmetry and cobalt site occupation drive the formation of two distinct magnetic phases. At 𝑥=1/4, the centrosymmetric structure (𝑃⁢6 3 /𝑚⁢𝑚⁢𝑐) promotes Co-Co interactions leading to the formation of an 𝐴-type antiferromagnetic structure phase with a transition temperature of 𝑇$^𝐴_𝑁$=169K. At 𝑥=1/3, the noncentrosymmetric structure (𝑃⁢6 3 ⁢22) induces a lower-temperature magnetic phase with 𝑇$^S_𝑁$=28K. We report the coexistence of both substructures within a superlattice, with a nuclear propagation vector of (1/3, 1/3, 0) relative to the host lattice. Single crystals of Co 0.28 ⁢NbSe 2 exhibit both magnetic transitions, with 𝑇$^𝐴_𝑁$ corresponding to the 𝑥∼1/4 phase and 𝑇$^S_𝑁$ corresponding to the 𝑥∼1/3 phase. Magnetic susceptibility and specific heat measurements confirm these transitions, although only the high-temperature 𝑇$^𝐴_𝑁$ phase significantly affects resistivity. We successfully isolate each phase in powder samples, while single crystals with an intercalation ratio of 𝑥=0.28 display the coexistence of both phases in a single sample. Using single-crystal neutron diffraction, we solved the magnetic structure of the high-temperature centrosymmetric phase (𝑇$^𝐴_𝑁$), and neutron powder diffraction revealed the double-𝑞 magnetic structure of the low-temperature noncentrosymmetric phase (𝑇$^S_𝑁$).

RKKY interaction↗
DOE OSTI2025

X-ray diffraction strains in laser-ablated aluminum, nickel, sodium, and invar: Pressures to 475 GPa

Dynamically compressed materials in longitudinal waves are described by two physical models: hydrostatic pressure, with equal, normal, principal stresses or material uniaxially strained in the wave propagation direction. These models are disparate, so experimental comparisons and evaluations are important. Polycrystalline material in a state of hydrostatic pressure will have no eccentricity of x-ray-diffracted Debye–Scherrer rings. A general three-dimensional solution of Bragg diffracted x rays based on principal crystallographic strains in the compression wave was found. The distortion of x-ray diffraction beams has been used for strain measurements; the analysis developed incorporates a strained reciprocal lattice and the incident x-ray beam. Strain-distorted Polanyi surfaces form an annulus of compression with an ellipsoid of revolution in reciprocal space, which is intersected by Ewald's sphere for Bragg diffraction. The in situ measurements for strain describe nanosecond diffraction evaluated using two planes, (hkl) and (h′k′l′), both in the same crystallographic phase. Diffraction from Al, Ni, Na, and Invar quantifies the compression axial strains in these materials: The compression axial ratios are 0.65, 1.05, 0.88, and 1.58 at pressures of 291, 402, 409, and 367 GPa for the respective materials. Crystal structure transformations with homogeneous pressurized stresses, mandating equal normal strains, should not be anticipated to agree with heterogeneous, uniaxially strained, and sheared crystalline phases. Measurements support in-plane strains increasing with pressure, p , in fcc and hcp aluminum as ε 22 = −0.21 p /TPa.

Alloys↗
DOE OSTI2022

Energy dispersive x-ray diffraction of luminescent powders: A complement to visible phosphor thermometry

Energy-dispersive x-ray diffraction of thermographic phosphors has been explored as a complementary temperature diagnostic to visible phosphor thermometry in environments where the temperature-dependent optical luminescence of the phosphors is occluded. Powder phosphor samples were heated from ambient to 300°C in incremental steps and probed with polychromatic synchrotron x rays; scattered photons were collected at a fixed diffraction angle of 3.9°. Crystal structure, lattice parameters, and coefficients of thermal expansion were calculated from the diffraction data. Finally, of the several phosphors surveyed, YAG:Dy, ZnO:Ga, and GOS:Tb were found to be excellent candidates for diffraction thermometry due to their strong, distinct diffraction peaks that shift in a repeatable and linear manner with temperature.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Structural changes upon magnetic ordering in magnetocaloric AlFe 2 B 2

With a Curie temperature just above room temperature, AlFe 2 B 2 is a useful magnetocaloric material composed of earth-abundant elements. Here, we employ temperature-dependent high-resolution synchrotron X-ray diffraction to establish with high certainty that the paramagnetic to ferromagnetic transition in AlFe 2 B 2 is of second order, showing no discontinuity in lattice parameters or cell volume. Nevertheless, the lattice parameters undergo anisotropic changes across the transition with distinct differences in the thermal expansion coefficients. While the $a$ and $b$ lattice parameters show a positive thermal expansion, $c$ shows a negative thermal expansion. We link these changes to the respective interatomic distances to determine the contribution of magnetism to the anisotropic structural evolution. The work underpins the possible role of magnetostructural coupling in driving the magnetocaloric effect in AlFe 2 B 2 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗