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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Three-Dimensional Predominance Volume Diagrams: The Ni-As-S-O System

The 3D predominance volume diagram (PVD) for the Ni-As-S-O system at 700 K (427 °C) was constructed using independent gases O{sub 2}, SO{sub 2}, and As{sub 4}O{sub 6}. The system has 15 four-condensed-phase invariant points. Invariant points, fixed by any combination of boundaries and condensed phases totaling four, were determined by a Gibb’s minimization routine that searched from a corner of the PVD along each undetermined line emanating from this and subsequently-identified invariants. The search direction was determined from the cross product of the two independent planes’ normal direction vectors. The 0.25 atm and 1.00 atm isobaric surfaces intersect the Ni{sub 3}As{sub 2}O{sub 8}, NiO, NiSO{sub 4}, Ni{sub 1−x}S, NiS{sub 2}, and Ni{sub 11}As{sub 8} phases. The 1.00 atm surface also intersects the NiAs phase. The PVD results agree with published ternary and quaternary phase diagram Alkemade lines. If the roasting of gersdorffite (NiAsS) parallels the roasting of enargite (Cu{sub 3}AsS{sub 4}), gersdorffite is expected to initially react irreversibly with O{sub 2} in the roasting gas to form NiS and NiSO{sub 4} topochemical layers with arsenic being expelled as As{sub 4}O{sub 6} gas and perhaps As{sub 4} gas once a diffusion-controlled topochemical reaction sequence is established. Thermochemical calculations showed that the formation of NiO from NiSO{sub 4} and Ni{sub 3}As{sub 2}O{sub 8}, if present, becomes more favorable as the temperature is increased with complete conversion to NiO above 1086 K and 1160 K (813 °C and 887 °C), respectively, at 1.00 atm.

36 MATERIALS SCIENCE↗
DOE OSTI2018

HipGISAXS

Implementation of a flexible Grazing Incidence Small-Angle Scattering (GISAXS). Simulation code based on the Distorted Wave Born Approximation (DWBA) theory that effectively utilizes the parallel processing power provided by graphic processors and multicore processors. This constitutes a handy tool for experimentalists facing a massive flux of data, allowing them to accurately simulate the GISAXS process and analyze the produced data. The software computes the diffraction image for any given super position of custom shapes or morphologies in a user-defined region of the reciprocal space for all possible grazing incidence angles and in-plane sample rotations. This flexibility then allows to easily tackle a wide range of possible sample structures such as nanoparticles o top of or embedded in a substrate or a multilayered structure. In cases where the sample displays regions of significant refractive index contrast, an algorithm has been implemented to perform a slicing of the sample along the vertical direction and compute the averaging refractive index profile to be used as the reference geometry of the unpertubed system. Preliminary tests show good agreement with experimental data for a variety of commonly encountered nanostructures.

Xiaoye, Sherry Li↗
DOE OSTI2024

Reconfigurable unitary transformations of optical beam arrays

Spatial transformations of light are ubiquitous in optics, with examples ranging from simple imaging with a lens to quantum and classical information processing in waveguide meshes. Multi-plane light converter (MPLC) systems have emerged as a platform that promises completely general spatial transformations, i.e., a universal unitary. However, until now, MPLC systems have demonstrated transformations that are far from general, e.g., converting from a Gaussian to Laguerre-Gauss mode. Here, we demonstrate the promise of an MLPC, the ability to impose an arbitrary unitary transformation that can be reconfigured dynamically. Specifically, we consider transformations on superpositions of parallel free-space beams arranged in an array, which is a common information encoding in photonics. We experimentally test the full gamut of unitary transformations for a system of two parallel beams and make a map of their fidelity. We obtain an average transformation fidelity of 0.85 ± 0.03. This high-fidelity suggests that MPLCs are a useful tool for implementing the unitary transformations that comprise quantum and classical information processing.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Strain profiles in ion implanted ceramic polycrystals: An approach based on reciprocal-space crystal selection

The determination of the state of strain in implanted materials is a key issue in the study of their mechanical stability. Whereas this question is nowadays relatively easily solved in the case of single crystals, it remains a challenging task in the case of polycrystalline materials. In this paper, we take benefit of the intense and parallel beams provided by third generation synchrotron sources combined with a two-dimensional detection system to analyze individual grains in polycrystals, hence obtaining “single crystal-like” data. The feasibility of the approach is demonstrated with implanted UO{sub 2} polycrystals where the in-depth strain profile is extracted for individual grains using numerical simulations of the diffracted signal. The influence of the implantation dose is precisely analyzed for several diffracting planes and grains. This work suggests that, at low fluences, the development of strain is mainly due to ballistic effects with little effect from He ions, independently from the crystallographic orientation. At higher fluences, the evolution of the strain profiles suggests a partial and anisotropic plastic relaxation. With the present approach, robust and reliable structural information can be obtained, even from complex polycrystalline ceramic materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Structural anisotropy in Sb thin films

Sb thin films have attracted wide interest due to their tunable band structure, topological phases, high electron mobility, and thermoelectric properties. We successfully grow epitaxial Sb thin films on a closely lattice-matched GaSb(001) surface by molecular beam epitaxy. We find a novel anisotropic directional dependence on their structural, morphological, and electronic properties. The origin of the anisotropic features is elucidated using first-principles density functional theory (DFT) calculations. The growth regime of crystalline and amorphous Sb thin films was determined by mapping the surface reconstruction phase diagram of the GaSb(001) surface under Sb 2 flux, with confirmation of structural characterizations. Crystalline Sb thin films show a rhombohedral crystal structure along the rhombohedral (211) surface orientation parallel to the cubic (001) surface orientation of the GaSb substrate. At this coherent interface, Sb atoms are aligned with the GaSb lattice along the [1̄10] crystallographic direction but are not aligned well along the [110] crystallographic direction, which results in anisotropic features in reflection of high-energy electron diffraction patterns, misfit dislocation formation, surface morphology, and transport properties. Our DFT calculations show that the preferential orientation of the rhombohedral Sb (211) plane may originate from the GaSb surface, where Sb atoms align with the Ga and Sb atoms on the reconstructed surface. The formation energy calculations confirm the stability of the experimentally observed structures. Our results provide optimal film growth conditions for further studies of novel properties of Bi 1-x Sb x thin films with similar lattice parameters and an identical crystal structure, as well as functional heterostructures of them with III–V semiconductor layers along the (001) surface orientation, supported by a theoretical understanding of the anisotropic film orientation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain

A challenge to simulating turbulent flow in multiscale atmospheric applications is the efficient generation of resolved turbulence motions over an area of interest. One approach is to apply small perturbations to flow variables near the inflow planes of turbulence-resolving simulation domains nested within larger mesoscale domains. While this approach has been examined in numerous idealized and simple terrain cases, its efficacy in complex terrain environments has not yet been fully explored. Here, we examine the benefits of the stochastic cell perturbation method (CPM) over real complex terrain using data from the 2017 Perdigão field campaign, conducted in an approximately 2-km wide valley situated between two nearly parallel ridges. Following a typical configuration for multiscale simulation using nested domains within the Weather Research and Forecasting (WRF) model to downscale from the mesoscale to a large-eddy simulation (LES), we apply the CPM on a domain with horizontal grid spacing of 150 m. At this resolution, spurious coherent structures are often observed under unstable atmospheric conditions with moderate mean wind speeds. Results from such an intermediate resolution grid are often nested down for finer, more detailed LES, where these spurious structures adversely affect the development of turbulence on the subsequent finer grid nest. We therefore examine the impacts of the CPM on the representation of turbulence within the nested LES domain under moderate mean flow conditions in three different stability regimes: weakly convective, strongly convective, and weakly stable. In addition, two different resolutions of the underlying terrain are used to explore the role of the complex topography itself in generating turbulent structures. We demonstrate that the CPM improves the representation of turbulence within the LES domain, relative to the use of high-resolution complex terrain alone. During the convective conditions, the CPM improves the rate at which smaller-scales of turbulence form, while also accelerating the attenuation of the spurious numerically generated roll structures near the inflow boundary. During stable conditions, the coarse mesh spacing of the intermediate LES domain used herein was insufficient to maintain resolved turbulence using CPM as the flow develops downstream, highlighting the need for yet higher resolution under even weakly stable conditions, and the importance of accurate representation of flow on intermediate LES grids.

17 WIND ENERGY↗
DOE OSTI2020

CP2K: An Electronic Structure and Molecular Dynamics Software Package - Quickstep: Efficient and Accurate Electronic Structure Calculations

CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular and biological systems. It is especially aimed at massively-parallel and linear-scaling electronic structure methods and state-of-the-art ab-initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post-Hartree-Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension. TDK has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 716142). VRR has been supported by the Swiss National Science Foundation in the form of Ambizione grant No. PZ00P2 174227 and RZK by the Natural Sciences and Engineering Research Council of Canada (NSERC) through Discovery Grants (RGPIN-2016-0505). GKS and CJM are supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. UK based work was funded under the embedded CSE programme of the ARCHER UK National Supercomputing Service (http://www.archer.ac.uk), grants eCSE03-011, eCSE06-6, eCSE08-9, eCSE13-17 and the EPSRC (EP/P022235/1) grant “Surface and Interface Toolkit for the Materials Chemistry Community". Computational resources were provided by the Swiss National Supercomputing Centre (CSCS) and Compute Canada. The generous allocation of computing time on the FPGA-based supercomputer “Noctua" at PC2 is kindly acknowledged.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Magnetic field-induced ferroelectricity in S = 1/2 kagome staircase compound PbCu 3 TeO 7

Ni 3 V 2 O 8 is an archetypical multiferroic material with a kagome staircase structure of S = 1 (Ni 2+ ) spins whose complex interplay between spin ordering and ferroelectricity has been studied for more than a decade. Here in this paper, we report a new kagome staircase compound PbCu 3 TeO 7 with Cu 2+ (S = 1/2) spins that exhibits two Néel temperatures at T N1 = 36 K and T N2 = 24 K, and a magnetic field (H)-induced electric polarization (P) below T N2 . Pyroelectric and magnetoelectric current measurements in magnetic fields up to 60 T reveal that for H||c of ~ 8.3 T, a spin-flop transition induces a transverse P||a with a magnitude of 15 µC/m 2 below T N2 . Furthermore, for a parallel configuration with P//H//a, two spin-flop transitions occur, the first at ~ 16 T with P//a of 14 µC/m 2 , and the second at ~ 38 T, where P disappears. Monte Carlo simulations based on 12 major exchange interactions uncover that a sinusoidal amplitude modulation of the spins occurs along the b-axis below T N1 and an incommensurate, proper screw-type spin order occurs in the ac-plane below T N2 . The simulation results show that P//a under H//c stems from a spin-flop transition facilitating an ab-plane-type spiral order, while the two successive spin-flop transitions for H//a result in spiral spin orders in the ab- and bc-planes. Based on the experimental and theoretical results, we establish field-induced magnetic and electric phase diagrams for the two H directions, demonstrating that the distorted kagome staircase structure with competing intra–interlayer interactions and lifted frustration creates a plethora of different noncollinear spin textures of S = 1/2 spins that in turn induce electric polarization.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Transverse force induced by a magnetized wake

The force on a test charge moving through a strongly magnetized plasma is calculated using linear response theory. Strong magnetization is found to generate a component of the force perpendicular to the velocity of the particle in the plane formed by the velocity and magnetic field vectors. Here, this transverse force is generated by an asymmetry with respect to the velocity vector in the induced electrostatic wake potential that is associated with the action of the Lorentz force on the background plasma. The direction depends on the speed of the test charge. If it is faster than a critical speed characteristic of the sound speed, it acts to reduce the component of velocity parallel to the magnetic field and to increase the gyroradius. In contrast, if the speed is below this critical speed, it acts to increase the velocity parallel to the magnetic field and to decrease the gyroradius. Because the transverse force is perpendicular to the velocity, it does not directly influence the total energy of the test charge. Nevertheless, it significantly alters the trajectory on a timescale associated with the Coulomb collision time.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Magnetic and superconducting anisotropy in Ni-doped RbEuFe 4 As 4 single crystals

We investigate the effect of Ni doping on the Fe site in single crystals of the magnetic superconductor RbEuFe 4 As 4 for doping concentrations of up to 4%. A clear suppression in the superconducting transition temperature is observed in specific-heat, resistivity, and magnetization measurements. Upon Ni doping, the resistivity curves shift up in a parallel fashion, indicating a strong increase of the residual resistivity due to scattering by charged dopant atoms while the shape of the curve and thus the electronic structure appear largely unchanged. The observed step Delta C/T c at the superconducting transition decreases strongly for increasing Ni doping in agreement with expectations based on a model of multiband superconductivity and strong interband pairing. The upper critical field slopes are reduced upon Ni doping for in-plane as well as out-of-plane fields, leading to a small reduction in the superconducting anisotropy. The specific-heat measurements of the magnetic transition reveal the same Berezinskii-Kosterlitz-Thouless behavior close to the transition temperature T m for all doping levels. The transition temperature is essentially unchanged upon doping. The in-plane to out-of-plane anisotropy of Eu magnetism observed at small magnetic fields is unaltered as compared to the undoped compound. In conclusion, all of these observations indicate a decoupling of the Eu magnetism from superconductivity and essentially no influence of Ni doping on the Eu magnetism in this compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

U 2 Ni 2 Sn and the origin of magnetic anisotropy in uranium compounds

Here, U 2 Ni 2 Sn is a member of a large family of intermetallic compounds with the tetragonal Mo 2 FeB 2 crystal structure. It orders antiferromagnetically at 25 K with propagation vector $q = (0, 0, \frac{1}{2})$. Magnetization, magnetoacoustic, and neutron-diffraction experiments on a single crystal provide evidence that the uranium moments align parallel to the $c$ axis with the anisotropy energy of ≈170 K, indicating that U 2 Ni 2 Sn can be classified as an Ising system. The results are at variance with previous studies on polycrystals, which indicated different magnetic structure, and which were incompatible with the $5f - 5f$ two-ion anisotropy model dominant in most U band systems. High-field magnetization studies exhibit a weak linear response for fields along the basal plane up to the highest field applied (60 T), while the $c$-axis magnetization curve exhibits three metamagnetic transitions at approximately 30, 39, and 50 T. The U magnetic moments of $0.87 μ_B$, the low magnetic entropy, and the enhanced Sommerfeld coefficient $γ$ = 187 mJ/mol f.u.K 2 suggest that U 2 Ni 2 Sn can be classified as an itinerant antiferromagnet with strong electron-electron correlations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Experimental and numerical analysis of pre-compressed masonry walls in two-way-bending with second order effects

The buckling behavior of slender unreinforced masonry (URM) walls subjected to axial compression and out-of-plane lateral loads is investigated through a combined experimental and numerical homogenizedapproach. After a preliminary analysis performed on a unit cell meshed by means of elastic FEs and non-linear interfaces, macroscopic moment-curvature diagrams so obtained are implemented at a structural level, discretizing masonry by means of rigid triangular elements and non-linear interfaces. The non-linear incremental response of the structure is accounted for a specific quadratic programming routine. In parallel, a wide experimental campaign is conducted on walls in two way bending, with the double aim of both validating the numerical model and investigating the behavior of walls that may not be reduced to simple cantilevers or simply supported beams. Panels investigated are dry-joint in scale square walls simply supported at the base and on a vertical edge, exhibiting the classical Rondelet’s mechanism. The results obtained are compared with those provided by the numerical model.

42 ENGINEERING↗
DOE OSTI2017

Advanced capabilities for materials modelling with Quantum ESPRESSO

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Potts-model critical manifolds revisited

We compute the critical polynomials for the q-state Potts model on all Archimedean lattices, using a parallel implementation of the algorithm of Ref. [1] that gives us access to larger sizes than previously possible. The exact polynomials are computed for bases of size 6 6 unit cells, and the root in the temperature variable v = e K -1 is determined numerically at q = 1 for bases of size 8 8. This leads to improved results for bond percolation thresholds, and for the Potts-model critical manifolds in the real (q; v) plane. In the two most favourable cases, we find now the kagome-lattice threshold to eleven digits and that of the (3; 12 2 ) lattice to thirteen. Our critical manifolds reveal many interesting features in the antiferromagnetic region of the Potts model, and determine accurately the extent of the Berker-Kadano phase for the lattices studied.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Enhancement of charge-neutral fermionic excitations near the spin-flop transition in the magnetic Kondo material YbIr 3 Si 7

The new Kondo material YbIr 3 Si 7 , similar to other Kondo insulators, has been reported to exhibit charge-neutral fermionic excitations through measurements of specific heat and thermal conductivity at low temperatures. We performed 29 Si-NMR on YbIr 3 Si 7 to investigate the magnetic response of charge-neutral fermions from a microscopic perspective. In low magnetic fields parallel to the c axis, a single NMR peak in the paramagnetic state splits into three peaks below TN. In contrast, only a slight shift of the single NMR peak was observed in high magnetic fields. This spectral change as a function of the c-axis magnetic field is interpreted as a spin-flop transition, at which the magnetic moments oriented along the c axis antiferromagnetic (AFM-I) phase are rotated to the ab plane with a ferromagnetic component along the c-axis (AFM-II phase). In the vicinity of the spin-flop magnetic field H M , the nuclear spin-lattice relaxation rate 1/T 1 was found to be proportional to temperature at low temperatures, indicating the existence of charge-neutral fermions. Furthermore, a peak of 1/T 1 versus the c-axis magnetic field suggests that the charge-neutral fermions in YbIr 3 Si 7 are closely related to its magnetic properties. Our findings shed light on the origin of charge-neutral fermions in insulators.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Unique Helical Magnetic Order and Field-Induced Phase in Trillium Lattice Antiferromagnet EuPtSi

Magnetic transition phenomena in cubic chiral antiferromagnet EuPtSi with T N = 4.0 K were investigated by means of single crystal neutron diffraction. At 0.3 K in the ground state, magnetic peaks emerge at positions represented by an ordering vector q 1 =(0.2,0.3,0) and its cyclic permutation. Upon heating, an additional magnetic peak splitting with hysteresis was uncovered at around T$*\atop{N}$~2.5 K, indicating the presence of a first-order commensurate–incommensurate transition with q$*\atop{1}$=(0.2,0.3,δ) (δ max ≃ 0.04) at T$*\atop{N}$. A half-polarized neutron scattering experiment for polarization parallel to the scattering vector revealed that polarization antiparallel to the scattering vector has stronger intensity in both magnetic phases. This feature clarifies the single chiral character of the helical structure with moments lying perpendicular to the ordering vector in both ordered states. Under a vertical magnetic field of 1.2 T for B ∥[1,1,1] at 1.9 K entering into the so-called A phase, magnetic peaks form characteristic hexagonal patterns in the equatorial scattering plane around nuclear peaks. An ordering vector q A ≃(±0.09,±0.20,∓0.28) of the A-phase has similar periodic length as q 1 , and could be the hallmark of a formation of skyrmion lattice in EuPtSi.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Controlling Cation-Cation Interactions in Uranyl Coordination Dimers by Varying the Length of the Dicarboxylate Linker

The chemistry of linear uranyl(V/VI) dioxo cations, [O yl –U–O yl ] +/2+ , is dominated by coordination of uranium in the equatorial plane. Effects of this constraint were evaluated by experiment and theory for gas-phase mixed-valence U V/VI coordination dimers in which uranyl moieties are linked by alkyl dicarboxylates, [(UO 2 + )(UO 2 2+ )(OOC-(CH 2 ) n-2 -COO 2– ) 2 ] – (n = 3–12). Faster O 2 -addition to dimers with short linkers n = 3 and 4, vs. n ≥ 5, suggests a structural difference. Computed structures with the shortest linkers have bridging dicarboxylates and nearly parallel, non-interacting uranyls. Longer linkers, n = 5–7, accommodate uranyl orientations with distinct U V –U VI end-on cation-cation interactions (CCIs), whereby Lewis base O yl from U V coordinates to the acid U VI , denoted as U V O yl ···U VI . The dimer structure for n = 8 has a U V –U VI side-on diamond-shape CCI, with U V O yl ···U VI and U VI O yl ···U V interactions. Addition of O 2 to the n = 4 and 5 dimers yields [(UO22+)2(OOC-(CH2)n-2-COO2–)2(O2–)]–, with U V oxidized to U VI and O 2 reduced to O 2 – . Whereas O 2 can associate to and oxidize the exposed U V center for dimers with n = 3 and 4, the more crowded U V site in the CCI structures inhibits O 2 addition. Finally, the results demonstrate rational structural control of uranyl-uranyl bonding and reactivity in small coordination complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Higher-order finite-difference formulation of periodic Orbital-free Density Functional Theory

We present a real-space formulation and higher-order finite-difference implementation of periodic Orbital-free Density Functional Theory (OF-DFT). Specifically, utilizing a local reformulation of the electrostatic and kernel terms, we develop a generalized framework for performing OF-DFT simulations with different variants of the electronic kinetic energy. In particular, we propose a self-consistent field (SCF) type fixed-point method for calculations involving linear-response kinetic energy functionals. In this framework, evaluation of both the electronic ground-state and forces on the nuclei are amenable to computations that scale linearly with the number of atoms. We develop a parallel implementation of this formulation using the finite-difference discretization. We demonstrate that higher-order finite-differences can achieve relatively large convergence rates with respect to mesh-size in both the energies and forces. Additionally, we establish that the fixed-point iteration converges rapidly, and that it can be further accelerated using extrapolation techniques like Anderson's mixing. We validate the accuracy of the results by comparing the energies and forces with plane-wave methods for selected examples, including the vacancy formation energy in Aluminum. Overall, the suitability of the proposed formulation for scalable high performance computing makes it an attractive choice for large-scale OF-DFT calculations consisting of thousands of atoms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗