Search NASA⌕ Search

SEARCH · Search NASA

Results for “crystal zoning”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

First-Principles Phonon Quasiparticle Theory Applied to a Strongly Anharmonic Halide Perovskite

Understanding and predicting lattice dynamics in strongly anharmonic crystals is one of the long-standing challenges in condensed matter physics. Here we propose a first-principles method that gives accurate quasiparticle (QP) peaks of the phonon spectrum with strong anharmonic broadening. On top of the conventional first-order self-consistent phonon (SC1) dynamical matrix, the proposed method incorporates frequency renormalization effects by the bubble self-energy within the QP approximation. We apply the developed methodology to the strongly anharmonic α-CsPbBr 3 that displays phonon instability within the harmonic approximation in the whole Brillouin zone. While the SC1 theory significantly underestimates the cubic-to-tetragonal phase transition temperature (T c ) by more than 50%, we show that our approach yields T c = 404–423 K, in excellent agreement with the experimental value of 403 K. Furthermore, we also demonstrate that an accurate determination of QP peaks is paramount for quantitative prediction and elucidation of phonon linewidth.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Enhanced Coherence in Superconducting Circuits via Band Engineering

In superconducting circuits interrupted by Josephson junctions, the dependence of the energy spectrum on offset charges on different islands is 2e periodic through the Aharonov-Casher effect and resembles a crystal band structure that reflects the symmetries of the Josephson potential. We show that higher-harmonic Josephson elements described by a cos(2φ) energy-phase relation provide an increased freedom to tailor the shape of the Josephson potential and design spectra featuring multiplets of flat bands and Dirac points in the charge Brillouin zone. Flat bands provide noise-insensitive energy levels, and consequently, engineering band pairs with flat spectral gaps can help improve the coherence of the system. We discuss a modified version of a flux qubit that achieves, in principle, no decoherence from charge noise and introduce a flux qutrit that shows a spin-1 Dirac spectrum and is simultaneously quite robust to both charge and flux noise.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Thermodynamics of Minerals Stable near Earth's Surface

Project “Thermodynamics of Minerals Stable Near the Earth’s Surface” uses specialized calorimetric techniques to obtain new thermochemical data for solid phases of interest in the Earth’s “critical zone”, the near surface regions of the planet most directly affecting and affected by human activity. Major activity was in three areas: manganese oxide materials, aluminum clusters which are precursors to aluminum oxyhydroxide precipitates, and zeolites. All these classes of minerals are potential carriers of heavy metals and radionuclides in the environment, both within their crystal structures and as adsorbed layers or colloids. Their thermodynamic stability, as well as the sequence of stability of competing phases, governs the aqueous solubility of contaminants (and nutrients) in soil, groundwater, and sediments. The thermodynamics of these phases is strongly affected by particle size and crystallinity, since they often occur as very fine particles which do not coarsen in the near-surface environment. Many of these materials exhibit extensive polymorphism, multicomponent solid solution, and variable hydration states. Thus, one must define and systematize important thermodynamic variables, since one cannot make measurements on each and every possible phase, particle size, and composition. A major finding of the work on manganese oxides was labile water-induced oxidation-reduction reactions. These will be studied further by a combination of thermodynamic and synchrotron-based spectroscopic methods, the latter in collaboration with Peggy O’Day at UC Merced. The adsorption of other species, including simple organics, on such redox-active surfaces will also be investigated by a combination of thermochemical and spectroscopic studies. Studies of the energetics of water adsorption on mineral surfaces will be expanded to emphasize the adsorption of CO2 and small organic molecules, relevant to soil, groundwater, and the subsurface environment. Gas adsorption calorimetry, immersion calorimetry, and solution calorimetry will be combined with appropriate analytical and spectroscopic techniques to obtain a comprehensive picture of the interactions and their energetics. The evolution of aqueous aluminum clusters to form aluminum oxyhydroxide precipitates will be studied in detail by a combination of calorimetric and structural methods applied to aqueous samples aged at room temperature. The energetics of new classes of clusters will be explored. The project addresses several common themes relevant to the broad mission of the Department of Energy. Thermochemical data for minerals stable near the Earth’s surface, though still incomplete, are essential for understanding both natural and anthropogenic processes that affect our very existence on this planet. Such data contribute to the fundamental underpinning for mitigation and management strategies for the extraction and use of energy. Fundamental thermodynamic and mechanistic understanding is required to model processes ranging from heavy metal pollution to nuclear waste disposal to climate change.

58 GEOSCIENCES↗
DOE OSTI2022

Quantifying Equiaxed vs Epitaxial Solidification in Laser Melting of CMSX-4 Single Crystal Superalloy

The competition between epitaxial vs. equiaxed solidification has been investigated in CMSX-4 single crystal superalloy during laser melting as practiced in additive manufacturing. Single-track laser scans were performed on a powder-free surface of directionally solidified CMSX-4 alloy with several combinations of laser power and scanning velocity. Electron backscattered diffraction (EBSD) mapping facilitated identification of new orientations, i.e., “stray grains” that nucleated within the fusion zone along with their area fraction and spatial distribution. Using high-fidelity computational fluid dynamics simulations, both the temperature and fluid velocity fields within the melt pool were estimated. This information was combined with a nucleation model to determine locations where nucleation has the highest probability to occur in melt pools. In conformance with general experience in metals additive manufacturing, the as-solidified microstructure of the laser-melted tracks is dominated by epitaxial grain growth; nevertheless, stray grains were evident in elongated melt pools. It was found that, though a higher laser scanning velocity and lower power are generally helpful in the reduction of stray grains, the combination of a stable keyhole and minimal fluid velocity further mitigates stray grains in laser single tracks.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Multifaceted aerosol effects on precipitation

Aerosols have been proposed to influence precipitation rates and spatial patterns from scales of individual clouds to the globe. However, large uncertainty remains regarding the underlying mechanisms and importance of multiple effects across spatial and temporal scales. Here, in this study, we review the evidence and scientific consensus behind these effects, categorized into radiative effects via modification of radiative fluxes and the energy balance, and microphysical effects via modification of cloud droplets and ice crystals. Broad consensus and strong theoretical evidence exist that aerosol radiative effects (aerosol–radiation interactions and aerosol–cloud interactions) act as drivers of precipitation changes because global mean precipitation is constrained by energetics and surface evaporation. Likewise, aerosol radiative effects cause well-documented shifts of large-scale precipitation patterns, such as the intertropical convergence zone. The extent of aerosol effects on precipitation at smaller scales is less clear. Although there is broad consensus and strong evidence that aerosol perturbations microphysically increase cloud droplet numbers and decrease droplet sizes, thereby slowing precipitation droplet formation, the overall aerosol effect on precipitation across scales remains highly uncertain. Global cloud-resolving models provide opportunities to investigate mechanisms that are currently not well represented in global climate models and to robustly connect local effects with larger scales. This will increase our confidence in predicted impacts of climate change.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Dynamical moment fragmentation in the all-in all-out pyrochlore Nd 2 ⁢Sn 2⁢ O 7

We report single crystal neutron spectroscopy and bulk characterization on hydrothermally grown Nd 2 Sn 2 O 7 , revealing magnetic moment fragmentation embedded within the all-in–all-out ordered state. The spectra reveal a nearly flat band with pinch-point momentum dependence accompanied by dispersive branches that produce half-moon features across multiple Brillouin zones. These defining signatures are captured quantitatively by a minimal dipolar-octupolar spin Hamiltonian, demonstrating excellent agreement between experiment and theory. The higher flat-mode energy helps account for the absence of dynamical interference in prior μSR studies, while the lack of any photon-like excitation imposes strict constraints on the proposed Coulombic antiferromagnet scenario. Furthermore, our results extend moment fragmentation to Nd 2 Sn 2 O 7 and identify it as a clean, tractable platform for quantitative exploration of emergent gauge field physics in frustrated magnets.

DC susceptibility measurements↗
DOE OSTI2024

Study of Microphysical Signatures Based on Spectral Polarimetry during the RELAMPAGO Field Experiment in Argentina

Weather radars with dual-polarization capabilities enable the study of various characteristics of hydrometeors, including their size, shape, and orientation. Radar polarimetric measurements, coupled with Doppler information, allow for analysis in the spectral domain. This analysis can be leveraged to reveal valuable insight into the microphysics and kinematics of hydrometeors in precipitation systems. This paper uses spectral polarimetry to investigate precipitation microphysics and kinematics in storm environments observed during the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) field experiment in Argentina. This study uses range–height indicator scan measurements from a C-band polarimetric Doppler weather radar deployed during the field campaign. Here, in this work, the impact of storm dynamics on hydrometeors is studied, including the size sorting of hydrometeors due to vertical wind shear. In addition, particle microphysical processes because of aggregation and growth of ice crystals in anvil clouds, as well as graupel formation resulting from the riming of ice crystals and dendrites, are also analyzed here. The presence of different particle size distributions because of the mixing of hydrometeors in a sheared environment and resulting size sorting has been reported using spectral differential reflectivity (sZ dr ) slope. Spectral reflectivity sZ h and sZ dr have also been used to understand the signature of ice crystal aggregation in an anvil cloud. The regions of pristine ice crystals are identified from vertical profiles of spectral polarimetric variables in anvil cloud because of sZ h < 0 dB and sZ dr values around 2 dB. It is also found that the growth process of these ice crystals causes a skewed bimodal sZ h spectrum due to the presence of both pristine ice crystals and dry snow. Next, graupel formation due to riming has been studied, and it is found that the riming process produces sZ h values of about 10 dB and corresponding sZ dr values of 1 dB. This positive sZ dr indicates the presence of needle/columnar secondary ice particles formed by ice multiplication processes in the riming zones. Last, the temporal evolution of a storm is investigated by analyzing changes in hydrometeor types with time and their influence on the spectral polarimetric variables.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Fluid Mixing during Phase Separation in Crystallizing White Dwarfs

Abstract Accurate models of cooling white dwarfs must treat the energy released as their cores crystallize. This phase transition slows the cooling by releasing latent heat and also gravitational energy, which results from phase separation: liquid C is released from the solid C/O core, driving an outward carbon flux. The Gaia color–magnitude diagram provides striking confirmation of this theory by revealing a mass-dependent overdensity of white dwarfs, indicating slowed cooling at the expected location. However, the observed overdensity is enhanced relative to the models. Additionally, it is associated with increased magnetism, suggesting a link between crystallization and magnetic field generation. Recent works aimed at explaining an enhanced cooling delay and magnetic field generation employ a uniform mixing prescription that assumes large-scale turbulent motions; we show here that these calculations are not self-consistent. We also show that thermohaline mixing is most likely efficient enough to provide the required chemical redistribution during C/O phase separation, and that the resulting velocities and mixing lengths are much smaller than previous estimates. These reduced fluid motions cannot generate measurable magnetic fields, suggesting any link with crystallization needs to invoke a separate mechanism. Finally, this mixing alters the chemical profiles, which in turn affects the frequencies of the pulsation modes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Unveiling the origins of work-hardening enhancement and mechanical instability in laser shock peened titanium

Laser shock-peening (LSP) produces complex gradients in microstructures and residual stresses, which enables fabrication of metallic engineering components with superior mechanical properties. In this work, we use non-destructive and spatially resolved high-energy X-ray diffraction (HE-XRD) to investigate the influences of LSP on microstructure, surface topography, and residual stress for high purity titanium plates. LSP is found to produce large compressive in-plane residual stresses near the peened surface which monotonically decay to zero about 2.5 mm below the surface. These properties were also tracked during in-situ tensile loading, allowing stress partitioning and work-hardening rates to be measured as a function of depth. The surface region is found to have the highest work-hardening rate and remain mechanically stable up to sample failure. In addition, a crystal rigid rotation along a transversal axis of about 27 & nbsp; was observed at large applied strain near the surface region, which is attributed to the formation of denser dispersed shear bands. Furthermore, a sudden drop in tensile stress was observed at a depth of similar to 160 mu m from the LSP surface, indicating the formation of a localized mechanical instability zone (LMIZ). The origin of this LMIZ could be attributed to the increase in shear stress induced by a load transfer from LSP surface due to the formation of denser dispersed shear bands. These observations indicate a localized transition in deformation behavior has occurred from dispersed shear banding to LMIZ and homogeneous deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

InAs Terahertz Metalens Emitter for Focused Terahertz Beam Generation

Metasurfaces have opened doors to combining multiple photonic functionalities in a single compact device. In particular, the ability to generate short terahertz (THz) pulses with precise wavefront engineering in a single THz metasurface redefined the role metasurfaces can play in THz systems. Here, an InAs metalens emitter which generates and focuses a THz pulse beam is demonstrated using a 130 nm thick InAs metasurface designed as a binary‐phase Fresnel zone plate. The THz beam is focused to a spot of ≈430 μm at 1 THz with a short focal length of 5 mm and large numerical aperture of 0.5. Nanoscale InAs Mie resonators comprising the metasurface enable THz generation with an amplitude as high as 20 times compared to plasmonic THz emitters and several times compared to a 1 mm thick ZnTe crystal. This InAs metasurface emitter provides a new paradigm for designing THz imaging, spectroscopy, and communication systems, where THz beam generation and shaping are performed with a single device without compromising the generation efficiency, while eliminating losses and avoiding limitations of phase matching of conventional nonlinear optics approaches.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Modulation of recombination zone position for white perovskite/organic emitter hybrid light-emitting devices

We report metal halide perovskites present specific challenges as emitters in large area, surface emission lighting devices. Among these challenges is the vast difference in carrier mobilities between the perovskite and many organic buffer layers typically used in such device fabrication as transport and blocking layers. This can make it difficult to engineer recombination to achieve white emitting devices generally. However, in this work, we introduce unique modulation of excitonic confinement within the perovskite layer of the device stack to control overall placement of the recombination zone. This results in a white light emitter that is bright and highly tunable, providing a path to realize white perovskite related light-emitting devices.

42 ENGINEERING↗
DOE OSTI2025

Tuning the magnetic properties of the spin-split antiferromagnet MnTe through pressure

The hexagonal antiferromagnet MnTe has attracted enormous interest as a prototypical example of a spin-compensated magnet in which the combination of crystal and spin symmetries lifts the spin degeneracy of the electron bands without the need for spin-orbit coupling, a phenomenon called nonrelativistic spin splitting (NRSS). Subgroups of NRSS are determined by the specific spin-interconverting symmetry that connects the two opposite-spin sublattices. In MnTe, this symmetry is rotation, leading to the subgroup with spin splitting away from the Brillouin zone center, often called altermagnetism. MnTe also has the largest spontaneous magnetovolume effect of any known antiferromagnet, implying strong coupling between the magnetic moment and volume. This magnetostructural coupling offers a potential knob for tuning the spin-splitting properties of MnTe. Here, we use neutron diffraction with in situ applied pressure to determine the effects of pressure on the magnetic properties of MnTe and further explore this magnetostructural coupling. We find that applying pressure significantly increases the Néel temperature, but decreases the ordered magnetic moment. We explain this as a consequence of strengthened magnetic exchange interactions under pressure, resulting in higher 𝑇 N , with a simultaneous reduction of the local moment of individual Mn atoms, described here via density functional theory. This reflects the increased orbital hybridization and electron delocalization with pressure. In conclusion, these results shed light on the competition between magnetic exchange interactions and the strength of individual magnetic moments and show that the magnetic properties of MnTe can be controlled by pressure, opening the door to improved properties for spintronic applications through tuning via physical or chemical pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Spin Berry points as crucial for ultrafast demagnetization

Laser-induced ultrafast demagnetization has puzzled researchers around the world for over two decades. Intrinsic complexity in electronic, magnetic and phononic subsystems is difficult to understand microscopically. So far, it is not possible to explain demagnetization using a single mechanism, which suggests a crucial piece of information still missing. In this paper, we return to a fundamental aspect of physics: spin and its change within each band in the entire Brillouin zone. We employ face-centered cubic (fcc) Ni as an example and use an extremely dense k mesh to map out spin changes for every band close to the Fermi level along all the high symmetry lines. To our surprise, spin angular momentum at some special k points abruptly changes from [Formula: see text] to [Formula: see text] simply by moving from one crystal momentum point to the next. This explains why intraband transitions, which the spin superdiffusion model is based upon, can induce a sharp spin moment reduction, and why electric current can change spin orientation in spintronics. These special k points, which are called spin Berry points [M. V. Berry, Proc. R. Soc. Lond. A 393 (1984) 45], are not random and appear when several bands are close to each other, so the Berry potential of spin majority states is different from that of spin minority states. Although within a single band, spin Berry points jump, when we group several neighboring bands together, they form distinctive smooth spin Berry lines. It is the band structure that disrupts those lines. Spin Berry points are crucial to laser-induced ultrafast demagnetization and spintronics.

Physics↗
DOE OSTI2025

Using multimodal X-ray computed tomography to advance 3D petrography: A non-destructive investigation of olivine inside a carbonaceous chondrite

Rocks form in three dimensions through time and studying them provides information from inside dynamic systems we cannot otherwise observe. Yet how we typically access the interior of the rocks themselves to gain that information may limit our understanding and influence how we reconstruct the processes that formed them. Here, we demonstrate combined non-destructive 3D X-ray imaging techniques that produce quantitative densitometric and crystallographic maps of entire individual grains inside a rock. Olivine grains throughout a sample of the carbonaceous chondrite Northwest Africa (NWA) 11346 were each characterized by size, shape, composition, zoning intensity, and crystallographic orientation. The addition of 3D crystallographic mapping to calibrated 3D densitometric analysis—used to calculate chemical composition—demonstrates a fully non-destructive petrographic method and provides unique insight. For instance, in our case, using crystallographic data to delineate individual grains and then measuring the 3D size, shape, and composition of each distinguishes variably reset relict grains from those later crystallized after a melting event. Intersection in a 2D slice could not have led to this interpretation because the integration of three-dimensional size, rounding, composition, location, and crystallographic orientation measured from each grain forms the key patterns. Multimodal laboratory X-ray imaging has strong potential to advance 3D petrography.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Absence of a bulk signature of a charge density wave in hard x-ray measurements of UTe 2

The long-sought pair density wave (PDW) is an exotic phase of matter in which charge density wave (CDW) order is intertwined with the amplitude or phase of coexisting, superconducting order. Originally predicted to exist in copper-oxides, circumstantial evidence for PDW order now exists in a variety of materials. Recently, scanning tunneling microscopy (STM) studies have reported evidence for a three-component CDW at the surface of the heavy-fermion superconductor, UTe 2 , persisting below its superconducting transition temperature [Aishwarya et al., Nature 618, 928933 (2023); Gu et al., Nature 618, 921927 (2023); LaFleur et al., Nat. Commun. 15, 4456 (2024)]. Here, in this study, we use hard x-ray diffraction measurements on crystals of UTe 2 at 𝑇 = 1.9 and 12 K to search for a bulk signature of this CDW. Using STM measurements as a constraint, we calculate the expected locations of CDW superlattice peaks and sweep a large volume of reciprocal space in search of a signature. We fail to find any evidence for a CDW near any of the expected superlattice positions in many Brillouin zones. We estimate an upper bound on the CDW lattice distortion of 𝑢 max ≲ 4×10 −3 Å. Our results suggest that the CDW observed in STM is either purely electronic, somehow lacking a signature in the lattice, or is restricted to the material surface.

Kengle, Caitlin S.↗
DOE OSTI2023

Realization of flat bands by lattice intercalation in kagome metals

Recently there has been intense interest in kagome metals, which are expected to host flat bands (FBs). However, the observed “FBs” are not flat over the whole two-dimensional Brillouin zone and overlap strongly with other bands. In fact, the FB does not truly exist in a default d-orbital kagome lattice, and the conditions for its existence in kagome metals are unknown. Here, based on tight-binding model analyses of the interplay between orbital and lattice symmetry, we establish such conditions. Additionally, we show that for a single d-orbital kagome lattice assuming large crystal field splitting (CFS), only the d z 2 orbital gives rise to a FB, while d xy , d x 2 -y 2 , d x⁢z , and d yz orbitals can only produce a FB with a rotated d-orbital basis so that they conform with the underlying kagome lattice symmetry. Most importantly, we demonstrate that both conditions of d-orbital rotation and large CFS can be ideally satisfied by intercalating the kagome lattice with a hexagonal sublattice without disrupting the destructive interference of FB wave function. Furthermore, we propose layered metalorganic frameworks as promising candidate kagome metals to realize FBs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Nanoscale microstructure and chemistry of transparent gahnite glass-ceramics revealed by atom probe tomography

The nanoscale microstructure and chemistry of a transparent gahnite glass-ceramic and its precursor glass were investigated using atom probe tomography, transmission electron microscopy, and nuclear magnetic resonance spectroscopy. In the annealed precursor glass, statistically significant ZrO clustering was observed along with Si depletion within 2 nm of the ZrO clusters. This clustering is expected to be the first step in the nucleation and crystallization of the nucleating agent, ZrO 2 . In the glass-ceramic, gahnite (ZnAl 2 O 4 ) crystallites were found to exist in proximal locations to ZrO 2 and not in a core-shell arrangement. The residual glass composition was directly measured by atom probe, showing higher concentrations of Al, Zn, and Zr than previously expected. At the interfaces between the crystallites and residual glass, no enrichment or depletion zones were found. Our findings provide answers to outstanding questions surrounding the nucleation and elemental partitioning, microstructure, and the residual glass composition of transparent gahnite glass-ceramics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Fermi surface topology and magnetotransport properties of superconducting Pd 3 Bi 2 Se 2

Pd 3 Bi 2 Se 2 is a rare realization of a superconducting metal with a non-zero topological invariant. Here, in this study, we report the growth of high-quality single crystals of layered Pd 3 Bi 2 Se 2 with a superconducting transition at T c ≈ 0.80 K and upper critical fields of ~10 mT and ~5 mT for the in plane and out-of-plane directions, respectively. Our density functional theory (DFT) calculations reveal three pairs of doubly degenerate bands crossing the Fermi level all displaying clear three dimensional dispersion consistent with the overall low electronic anisotropy (<2). The multiband electronic nature of Pd 3 Bi 2 Se 2 is evident in magneto-transport measurements, yielding a sign changing Hall resistivity at low temperatures. The magnetoresistance is non-saturating and follows Kohler’s scaling rule. We interpret the magneto-transport data in terms of open orbits that are revealed in the DFT calculated Fermi surface. de Haas-van Alphen (dHvA) oscillation measurements using torque magnetometry on single crystals yield four frequencies for out-of-plane fields: F α = (150 ± 26) T, F β = (293 ± 10) T, F γ = (375 ± 20) T and F η = (1017 ± 12) T, with the low frequency dominating the spectrum. Through the measurement of angular dependent dHvA oscillations and DFT calculations we identify the F α frequency with an approximately ellipsoidal electron pocket centered on the L 2 point of the Brillouin zone. Lifshitz-Kosevich analysis of the dHvA oscillations reveals a small cyclotron effective mass m* = (0.11 ± 0.02)m 0 and a nontrivial Berry phase for the dominant orbit. The presence of nontrivial topology in a bulk superconductor positions Pd 3 Bi 2 Se 2 as a potential candidate for exploring topological superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗