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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Effect of Laser Beam Profile on Rotating Lattice Single Crystal Growth in Sb2S3 Model Glass

Laser heating of chalcogenide glasses has successfully produced rotating lattice single crystals through a solid-solid transformation. To better understand the nature of complex, orientation-dependent lattice rotation, we designed heat profiles of the continuous wave laser by beam shaping, fabricated larger Sb2S3 crystal dots in Sb2S3 glass, and investigated the lattice rotation where the crystal could grow in all radial directions under a circular thermal gradient. The results show that the rate of lattice rotation is highly anisotropic and depends on crystallographic direction. The nature of this rotation is the same in crystals of different orientation relative to the surface. The growth directions that align with the slip planes show the highest rate of rotation and the rotation rate gradually decreases away from this direction. Additionally, the presence of multiple growth directions results in a complicated rotation system. We suggest that the growth front influences the density of dislocations introduced during growth under confinement and thus affects the lattice rotation rate in these crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Large-Area Periodic Arrays of Atomically Flat Single-Crystal Gold Nanotriangles Formed Directly on Substrate Surfaces

The advancement of nanoenabled wafer-based devices requires the establishment of core competencies related to the deterministic positioning of nanometric building blocks over large areas. Within this realm, plasmonic single-crystal gold nanotriangles represent one of the most attractive nanoscale components but where the formation of addressable arrays at scale has heretofore proven impracticable. In this work, a benchtop process is presented for the formation of large-area periodic arrays of gold nanotriangles. The devised growth pathway sees the formation of an array of defect-laden seeds using lithographic and vapor-phase assembly processes followed by their placement in a growth solution promoting planar growth and threefold symmetric side-faceting. The nanotriangles formed in this high-yield synthesis distinguish themselves in that they are epitaxially aligned with the underlying substrate, grown to thicknesses that are not readily obtainable in colloidal syntheses, and present atomically flat pristine surfaces exhibiting gold atoms with a close-packed structure. As such, they express crisp and unambiguous plasmonic modes and form photoactive surfaces with highly tunable and readily modeled plasmon resonances. The devised methods, hence, advance the integration of single-crystal gold nanotriangles into device platforms and provide an overall fabrication strategy that is adaptable to other nanomaterials.

42 ENGINEERING↗
DOE OSTI2020

Impact of krypton irradiation on a single crystal tungsten: Multi-modal X-ray imaging study

Understanding microstructural and strain evolutions induced by noble gas production in the nuclear fuel matrix or plasma-facing materials is crucial for designing next generation nuclear reactors, as they are responsible for volumetric swelling and catastrophic failure. In this paper we describe a multimodal approach combining synchrotron-based nanoscale X-ray imaging techniques with atomic-scale electron microscopy techniques for mapping chemical composition, morphology and lattice distortion in a single crystal W induced by Kr irradiation. We report that Kr-irradiated single crystal W undergoes surface deformation, forming Kr containing cavities. Furthermore, positive strain fields are observed in Kr-irradiated regions, which lead to compression of underlying W matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structure of Pb(Fe 2/3 W 1/3 )O 3 single crystals with partial cation order

Despite intensive studies on the complex perovskite Pb(Fe 2/3 W 1/3 )O 3 (PFWO) relaxor, understanding the exact nature of its multifunctional properties has remained a challenge for decades. In this work we report a comprehensive structural study of the PFWO single crystals using a combination of synchrotron X-ray diffraction and high-resolution electron microscopy. The set of {h + ½, k + ½, l + ½} superlattice reflections was observed for the first time based on single-crystal synchrotron X-ray experiments (100–450 K) and transmission electron microscopy investigations, which indicates some kind of B-cation ordering in PFWO which had been thought to be totally disordered. It was found that (1) the crystal structure of PFWO should be described by a partly ordered cubic perovskite (i.e. Fm – 3m ), (2) the weak ferromagnetic properties and excess magnetic moment of PFWO can be understood based on non-random distribution of Fe cations between the 4a and 4b sites, and (3) the Pb displacement disorder is present in this material and the cations are probably displaced along the <100> directions. The X-ray diffraction results of this investigation show that partial cation ordering indeed exists in PFWO, which makes it necessary to revisit the generally accepted interpretations of the results obtained up to date. In agreement with X-ray diffraction study the main results of TEM study include: (1) a long range order that can be described with the Fm – 3m symmetry is reliably detected, (2) the coherence length of that long range order is in the order of 1–2 nm and (3) no remarkable chemical inhomogeneity is found in the tested PFWO crystal, excluding the possibility of a compositional ordering arising from substitutional defects in the perovskite structure.

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

Single-crystal elasticity of (Al,Fe)-bearing bridgmanite up to 82 GPa

Abstract Thermoelastic properties of mantle candidate minerals are essential to our understanding of geophysical phenomena, geochemistry, and geodynamic evolutions of the silicate Earth. However, the lower-mantle mineralogy remains much debated due to the lack of single-crystal elastic moduli (Cij) and aggregate sound velocities of (Al,Fe)-bearing bridgmanite, the most abundant mineral of the planet, at the lower mantle pressure-temperature (P-T) conditions. Here we report single-crystal Cij of (Al,Fe)-bearing bridgmanite, Mg0.88Fe0.1Al0.14Si0.90O3 (Fe10-Al14-Bgm) with Fe3+/ΣFe = ~0.65, up to ~82 GPa using X-ray diffraction (XRD), Brillouin light scattering (BLS), and impulsive stimulated light scattering (ISLS) measurements in diamond-anvil cells (DACs). Two crystal platelets with orientations of (–0.50, 0.05, –0.86) and (0.65, –0.59, 0.48), that are sensitive to deriving all nine Cij, are used for compressional and shear wave velocity (νP and νS) measurements as a function of azimuthal angles over 200° at each experimental pressure. Our results show that all Cij of singe-crystal Fe10-Al14-Bgm increase monotonically with pressure with small uncertainties of 1–2% (±1σ), except C55 and C23, which have uncertainties of 3–4%. Using the third-order Eulerian finite-strain equations to model the elasticity data yields the aggregate adiabatic bulk and shear moduli and respective pressure derivatives at the reference pressure of 25 GPa: KS = 326 ± 4 GPa, µ = 211 ± 2 GPa, KS′ = 3.32 ± 0.04, and µ′ = 1.66 ± 0.02 GPa. The high-pressure aggregate νS and νP of Fe10-Al14-Bgm are 2.6–3.5% and 3.1–4.7% lower than those of MgSiO3 bridgmanite end-member, respectively. These data are used with literature reports on bridgmanite with different Fe and Al contents to quantitatively evaluate pressure and compositional effects on their elastic properties. Comparing with one-dimensional seismic profiles, our modeled velocity profiles of major lower-mantle mineral assemblages at relevant P-T suggest that the lower mantle could likely consist of about 89 vol% (Al,Fe)-bearing bridgmanite. After considering uncertainties, our best-fit model is still indistinguishable from pyrolitic or chondritic models.

Geochemistry & Geophysics↗
DOE OSTI2020

High frequency atomic tunneling yields ultralow and glass-like thermal conductivity in chalcogenide single crystals

Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions and crystalline imperfections leads to a non-monotonic trend of thermal conductivity with temperature. Defect-free crystals that exhibit the glassy trend of low thermal conductivity with a monotonic increase with temperature are desirable because they are intrinsically thermally insulating while retaining useful properties of perfect crystals. However, this behavior is rare, and its microscopic origin remains unclear. Here, we report the observation of ultralow and glass-like thermal conductivity in a hexagonal perovskite chalcogenide single crystal, BaTiS 3 , despite its highly symmetric and simple primitive cell. Elastic and inelastic scattering measurements reveal the quantum mechanical origin of this unusual trend. A two-level atomic tunneling system exists in a shallow double-well potential of the Ti atom and is of sufficiently high frequency to scatter heat-carrying phonons up to room temperature. While atomic tunneling has been invoked to explain the low-temperature thermal conductivity of solids for decades, our study establishes the presence of sub-THz frequency tunneling systems even in high-quality, electrically insulating single crystals, leading to anomalous transport properties well above cryogenic temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Symmetrization of Strong Hydrogen Bond under High Pressure in Bihydroxide-Ion-Containing NaCu 2 (SO 4 ) 2 ·H 3 O 2 Revealed by Experimental Charge Density, Single-Crystal Electron Diffraction, and Neutron Diffraction Studies

In minerals and inorganic compounds, strong hydrogen bonding can lead to the formation of complex ionic species such as the H 3 O 2 – bihydroxide anion and Zundel cation H 5 O 2 + . We studied [NaCu 2 (SO 4 ) 2 ·H 3 O 2 ] natrochalcite, which contains bihydroxide anions and undergoes hydrogen bond symmetrization at the lowest pressure reported so far among inorganic compounds. Hydrogen bond symmetrization leads to changes in the bulk modulus, seismic wave velocities, and proton mobility and plays a primary role in high-temperature superconductivity, but its characteristics are not well understood due to a lack of systematic studies and limitations of experimental methods sensitive to this subtle change. In this work, we applied experimental charge density analysis based on in situ single-crystal X-ray diffraction data, along with the single-crystal neutron and electron diffraction experiments, to probe the behavior of hydrogen atoms during the hydrogen bond symmetrization process under high-pressure conditions. On the way to the symmetrical H-bonding, natrochalcite undergoes a series of complex redistributions of electron density, which we trace with multipole refinement and detailed analysis of changes in the Laplacian of electron density values. Additionally, we deconvoluted the equation of state (volume of the unit cell vs pressure relation) into the atomic equation of states describing dependencies of atomic charges or volumes vs pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Economical Laue x-ray diffraction using photographic film and orientation of single crystals

Many Laue x-ray diffraction systems using the Polaroid XR-7 Land Diffraction Cassette camera became inactive after production of the required high sensitivity Polaroid T-57 instant film ceased. This Tutorial reports on a low-cost solution using the readily available replacement film with push processing to increase the effective film speed. The use of this film in the polaroid camera is described along with film development and digitization. The orientation of single crystals with the obtained data and free software is explained. A simple method to prepare single crystals with surfaces perpendicular to a desired crystallographic orientation is described. The content of this Tutorial may prove beneficial for educational and research laboratories.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Graphene nanopattern as a universal epitaxy platform for single-crystal membrane production and defect reduction

Heterogeneous integration of single-crystal materials offers great opportunities for advanced device platforms and functional systems. Although substantial efforts have been made to co-integrate active device layers by heteroepitaxy, the mismatch in lattice polarity and lattice constants has been limiting the quality of the grown materials. Layer transfer methods as an alternative approach, on the other hand, suffer from the limited availability of transferrable materials and transfer-process-related obstacles. Here, we introduce graphene nanopatterns as an advanced heterointegration platform that allows the creation of a broad spectrum of freestanding single-crystalline membranes with substantially reduced defects, ranging from non-polar materials to polar materials and from low-bandgap to high-bandgap semiconductors. Additionally, we unveil unique mechanisms to substantially reduce crystallographic defects such as misfit dislocations, threading dislocations and antiphase boundaries in lattice- and polarity-mismatched heteroepitaxial systems, owing to the flexibility and chemical inertness of graphene nanopatterns. More importantly, we develop a comprehensive mechanics theory to precisely guide cracks through the graphene layer, and demonstrate the successful exfoliation of any epitaxial overlayers grown on the graphene nanopatterns. Furthermore, this approach has the potential to revolutionize the heterogeneous integration of dissimilar materials by widening the choice of materials and offering flexibility in designing heterointegrated systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Lattice Dynamics and Optoelectronic Properties of Vacancy-Ordered Double Perovskite Cs 2 TeX 6 (X = Cl – , Br – , I – ) Single Crystals

The soft, dynamic lattice of inorganic lead halide perovskite CsPbX 3 (X = Cl ⁻ , Br ⁻ , I ⁻ ) leads to the emergence of many interesting photophysical and optoelectronic phenomena. However, probing their lattice dynamics with vibrational spectroscopy remains challenging. The influence of the fundamental octahedral building block in the perovskite lattice can be better resolved in zero-dimensional (0D) vacancy-ordered double perovskites of form A 2 BX 6 . Here we study Cs 2 TeX 6 (X = Cl ⁻ , Br ⁻ , I ⁻ ) single crystals to yield detailed insight into the fundamental octahedral building block and to explore the effect that its isolation in the crystal structure has on structural and electronic properties. The isolated [TeX 6 ] 2- octahedral units serve as the vibrational, absorbing, and emitting centers within the crystal. Serving as the vibrational centers, the isolated octahedra inform the likelihood of a random distribution of 10 octahedral symmetries within the mixed-halide spaces, as well as the presence of strong exciton-phonon coupling and anharmonic lattice dynamics. Serving as the absorbing and emitting centers, the isolated octahedra exhibit compositionally tunable absorption (1.50-3.15 eV) and emission (1.31-2.11 eV) energies. Due to greater molecular orbital overlap between neighboring octahedra with increasing halide anion size, there is a transition from a more molecule-like electronic structure in Cs 2 TeCl 6 and Cs 2 TeBr 6 -as expected from the effective 0D nature of these single crystals-to a dispersive electronic structure in Cs 2 TeI 6 , typical of three-dimensional (3D) bulk single crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The Water-Fe-Pressure dependent single-crystal elastic properties of wadsleyite: Implications for the seismic anisotropy in the upper Mantle Transition Zone

Recent seismic studies suggest an anisotropic Mantle Transition Zone (MTZ) in areas adjacent to subducted slabs. Wadsleyite is the main anisotropy contributor in the upper MTZ, therefore the interpretation of these seismic observations requires the knowledge of single-crystal elastic moduli (C ij s) and the deformation-induced lattice preferred orientation (LPO) of wadsleyite. Wadsleyite can host up to 3 wt% water in its crystal structure as point defects in the form of hydroxyl groups, however, the combined effect of water content, Fe content, and pressure on the C ij s of wadsleyite remains unclear. In this study, we measured the high-pressure single-crystal elasticity of a synthetic hydrous Fe-bearing wadsleyite (0.14(5) wt% water, Fe#=9.4, Fe 3+ /ΣFe=0.3) up to 18.2 (2) GPa. In combination with previous experimental data, we separated the effects of pressure, water, and Fe contents on the Cijs and intrinsic elastic anisotropy of wadsleyite. Overall, our results suggest that the intrinsic elastic anisotropy of wadsleyite decreases with pressure, water, and Fe contents. At 15 GPa, increasing the water content by 0.1 wt% or Fe# by 1 decreases the V P and V S anisotropy of wadsleyite by ~1.1-1.3%, and ~0.8-1.3% in average, respectively. Combined with the LPO determined in previous deformation experiments, we modeled the seismic anisotropy in the upper MTZ generated by a sub-vertical mantle flow near cold subducted slabs and a sub-horizontal mantle flow in the ambient mantle. In both scenarios, the LPO of wadsleyite leads to V SV (vertically polarized shear wave velocity) > V SH (horizontally polarized shear wave velocity). Our results suggest that wadsleyite may account for a weak anisotropic MTZ (<1%) on the global scale. Considering the fact that water decreases the elastic anisotropy but promotes LPO of wadsleyite, seismic anisotropy may not be a good water sensor.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Unprecedented non-hysteretic superelasticity of [001]-oriented NiCoFeGa single crystals

Superelasticity associated with the martensitic transformation has found a broad range of engineering applications. However, the intrinsic hysteresis and temperature sensitivity of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. In this paper, we report a large superelasticity up to 15.2% strain in [001]-oriented NiCoFeGa single crystals, exhibiting non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. In situ synchrotron X-ray diffraction measurements show that the superelasticity is correlated with a stress-induced continuous variation of lattice parameter accompanied by structural fluctuation. Neutron diffraction and electron microscopy observations reveal an unprecedented microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the superelasticity. The discovery of the large elasticity related to the entangled structure paves the way for exploiting elastic strain engineering and development of related functional materials. NiCoFeGa single crystals exhibit large non-hysteretic superelasticity over broad temperature and composition ranges. It is attributed to the continuous phase transition with applied stress, which is related to the fluctuation of entangled ordered and disordered crystal structures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Spatial description of dislocation nucleation in the shock response of single-crystal aluminum

Nonequilibrium molecular dynamics simulations of shock loaded single-crystal Al in the $\langle$100$\rangle$, $\langle$110$\rangle$, $\langle$111$\rangle$, and $\langle$123$\rangle$ orientations are conducted to study elastic and plastic shockwave formation and details associated with dislocation activity. A computer vision-based approach is implemented to capture the presence of dislocations and describe their spatial characteristics in the zone of nucleation behind the propagating shockwave. The methodology developed relies on the sequences of images extracted during shock loading that show dislocation activity within a cross section of the sample. Results reveal that the spacing between activated slip systems is orientation dependent and exhibits a modest reduction for the $\langle$100$\rangle$ and $\langle$111$\rangle$ orientations as shock pressure increases. Comparisons are made to existing theoretical models. Such relationships between shock pressure and dislocation activity, extracted from molecular dynamics simulations, can be used to inform higher length scale simulations or modeling of dislocation-based plasticity during shock.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetisation and magneto-transport measurements on CeBi single crystals

In this study, we report the synthesis of CeBi single crystals out of Bi self-flux and a systematic study of the magnetic and transport properties with varying temperature and applied magnetic fields. From these R(T, H) and M(T, H) data, we could assemble the field-temperature (H⁻T) phase diagram for CeBi and visualise the three-dimensional M⁻T⁻H surface. In the phase diagram, we identify regions with well-defined magnetisation values and identify a new phase region. The magnetoresistance (MR) in the low-temperature regime shows, above 6T a power-law, non-saturated behaviour with large MR (~3 × 10 5 % at 2K and 13.95T), along with Shubnikov–de Haas oscillations. With increasing temperatures, MR decreases, and then becomes negative for T ⪆10 K . This crossover in MR seems to be unrelated to any specific magnetic or metamagnetic transitions, but rather is associated with changing from a low-temperature normal metal regime with little or no scattering from the Ce 3 + moments and an anomalously large MR, to increased scattering from local Ce moments and a negative MR as temperature increases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Possible unconventional order parameter in single crystals of SrPt 3 P superconductor

Here, anisotropic properties of single crystals of SrPt 3 P were studied using London penetration depth and electrical resistivity measurements. The upper critical field, $H_{c2}(T)$, was determined from four-probe electrical resistivity measurements for three orthogonal directions of a magnetic field with respect to the crystal. The London penetration depth, $λ(T)$, was determined from the magnetic susceptibility of the Meissner–London state measured using a tunnel-diode resonator technique. Whereas $H_{c2}(T)$ and the normal-state $ρ(T)$ are practically identical for all three magnetic field orientations, the London penetration depth shows significant unidirectional anisotropy. The low-temperature $λ(T)$ is exponentially attenuated when a small excitation radiofrequency magnetic field, $H_{rf}$, is applied along the c"-direction, in which case screening currents flow in the a"b"-plane, while for the other two orientations, $H_{rf}$∥ a" and $H_{rf}$ ∥ b", the London penetration depth shows a much stronger, $λ(T)$ ~ T 2 , variation. Such unusual and contrasting behavior of the two anisotropies, $γ_{H}$(T) = $H_{c2}$/$H_{c2,c}$ = $ξ_{ab}$/$ξ_{c}$ and $γ_{λ}$(T) = $λ_{c}$\$λ_{ab'}$, imposes significant constraints on the possible order parameter. Although our measurements are insufficient to derive conclusively the superconducting gap anisotropy, the order parameter with two point nodes and a modulation in the perpendicular direction is qualitatively consistent with the experimental observations.

anisotropic superconducting gap↗
DOE OSTI2020

Sub-molecular structural relaxation at a physisorbed interface with monolayer organic single-crystal semiconductors

Arranging molecules into highly symmetric, topological crystal structures has been recognized as the best approach to functionalize electronic properties in molecular crystals, where the constituent molecules have been assumed to be rigid in shape. Here, in striking contrast, we demonstrate that the molecules in a monolayer organic crystal can undergo a significant deformation in proximity to the substrate, which is reflected by an asymmetry in the electron density profile. X-ray reflectivity and X-ray absorption spectroscopies in conjunction with density-functional theory calculations reveal that the highly planarized π-core are deformed into a bent shape, while the bulk lattice parameters are maintained. The molecular shape change is found to be perfectly suppressed in a bilayer single crystal, which leads to a 40% increase in mobility in the bilayer crystal. Our finding of a unique, sub-molecular scale shape change in monolayer single crystals can offer possibilities for functionalizing electrical properties via nano-scale physisorption.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Oxygen vacancy-induced ferroelectric effect in (111) strontium titanate single crystals controls photoelectrochemical water oxidation

Ferroelectric materials, such as tetragonal BaTiO 3 , have a permanent electric polarization that can be controlled with an external electric field, however, a ferroelectric polarization in cubic SrTiO 3 is forbidden by the higher symmetry of the lattice. Here we demonstrate that hydrogen annealed SrTiO 3−x single crystals can be polarized electrically, and that the polarization controls the activity for photoelectrochemical water oxidation, a pathway to solar hydrogen fuel. Specifically, it is observed that the anodic water oxidation photocurrent increases from 0.99 to 2.22 mA cm −2 at 1.23 V RHE (60 mW cm −2 , UV illumination) or decreases to 0.50 mA cm −2 after electric polarization of hydrogen-annealed (111) SrTiO 3−x single crystals in forward or reverse direction. The polarization also modifies the surface photovoltage signal of the material and its flat band potential, based on Mott–Schottky measurements. These observations are attributed to the formation of an electric dipole at the (111) SrTiO 3−x surface, which alters the potential drop across the depletion layer at the solid–liquid junction, and with it the electron transfer barrier. Density functional theory calculations confirm that an electric dipole can result from the movement of oxygen vacancies between the surface or sub-surface layers of SrTiO 3−x . The filling of these surface oxygen vacancies is the probable cause for the observed disappearance of the electric polarization after 24 h storage in air and 48 h in argon. Overall, this work establishes a new surface-based ferroelectric effect in SrTiO 3−x and its use for solar energy conversion during photoelectrochemical water oxidation. Because oxygen vacancy defects are common, similar electric polarization effects are to be expected in other metal oxides.

Assavachin, Samutr [University of California, Davi↗