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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Single Ru(II) Ions on Ceria as a Highly Active Catalyst for Abatement of NO

Atom trapping leads to catalysts with atomically dispersed Ru 1 O 5 sites on (100) facets of ceria, as identified by spectroscopy and DFT calculations. This is a new class of ceria-based materials with Ru properties drastically different from the known M/ceria materials. They show excellent activity in catalytic NO oxidation, a critical step that requires use of large loadings of expensive noble metals in diesel aftertreatment systems. Ru 1 /CeO 2 is stable during continuous cycling, ramping, and cooling as well as the presence of moisture. Furthermore, Ru 1 /CeO 2 shows very high NO x storage properties due to formation of stable Ru–NO complexes as well as a high spill-over rate of NO x onto CeO 2 . Only ~0.05 wt % of Ru is required for excellent NO x storage. Ru 1 O 5 sites exhibit much higher stability during calcination in air/steam up to 750 °C in contrast to RuO 2 nanoparticles. Here we clarify the location of Ru(II) ions on the ceria surface and experimentally identify the mechanism of NO storage and oxidation using DFT calculations and in situ DRIFTS/mass spectroscopy. Moreover, we show excellent reactivity of Ru 1 /CeO 2 for NO reduction by CO at low temperatures: only 0.1–0.5 wt % of Ru is sufficient to achieve high activity. Modulation-excitation in situ infrared and XPS measurements reveal the individual elementary steps of NO reduction by CO on an atomically dispersed Ru ceria catalyst, highlighting unique properties of Ru 1 /CeO 2 and its propensity to form oxygen vacancies/Ce +3 sites that are critical for NO reduction, even at low Ru loadings. Our study highlights the applicability of novel ceria-based single-atom catalysts to NO and CO abatement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Supervised learning of a chemistry functional with damped dispersion

Abstract Kohn–Sham density functional theory is widely used in chemistry, but no functional can accurately predict the whole range of chemical properties, although recent progress by some doubly hybrid functionals comes close. Here, we optimized a singly hybrid functional called CF22D with higher across-the-board accuracy for chemistry than most of the existing non-doubly hybrid functionals by using a flexible functional form that combines a global hybrid meta-nonseparable gradient approximation that depends on density and occupied orbitals with a damped dispersion term that depends on geometry. We optimized this energy functional by using a large database and performance-triggered iterative supervised training. We combined several databases to create a very large, combined database whose use demonstrated the good performance of CF22D on barrier heights, isomerization energies, thermochemistry, noncovalent interactions, radical and nonradical chemistry, small and large systems, simple and complex systems and transition-metal chemistry.

Liu, Yiwei (ORCID:0000000288126163)↗
DOE OSTI2023

Ultrathin electron and proton-conducting membranes for nanoscale integrated artificial photosystems

Reducing the thickness of separation membranes without compromising their selectivity and robustness is the most effective way of maximizing the areal conductivity. This is especially important for the integration of visible light-driven water oxidation and carbon dioxide (or proton) reduction into a complete artificial photosystem on the shortest possible length scale – the nanoscale – because of the efficiency advantages over macroscale photosystems. In addition to their excellent separation property, ultrathin membranes of 10 nm thickness or less need to exhibit sufficient electrical and proton conductivity in order for the photocatalytic rates to keep up with the photon flux at maximum solar intensity. Furher, two materials, graphene and amorphous silica with embedded molecular wires, have emerged as promising ultrathin membranes for the development of nanoscale integrated solar-fuel systems. Moreover, electrically conducting metal–organic or covalent–organic frameworks can be used to fabricate high surface area-supports that enable the use of molecular catalysts and/or light absorbers at an adequate areal density for nanoscale integration with graphene membranes. Following an overview of the electron and proton conductivity of these ultrathin materials and recent examples of photoelectrocatalytic applications that take advantage of some but not all the properties that constitute a complete functional membrane, the status and future opportunities for complete nanoscale integrated photosystems featuring an ultrathin membrane are discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Relativistic two-component projection-based quantum embedding for open-shell systems

In this work, we present a relativistic quantum embedding formalism capable of variationally treating relativistic effects, including scalar-relativity and spin–orbit coupling. We extend density functional theory (DFT)-in-DFT projection-based quantum embedding to a relativistic two-component formalism, where the full spin magnetization vector form is retained throughout the embedding treatment. To benchmark various relativistic embedding schemes, spin–orbit splitting of the nominally t 2g valence manifold of W(CO) 6 , exchange coupling of [(H 3 N) 4 Cr(OH) 2 Cr(NH 3 ) 4 ] 4+ , and the dissociation potential curve of WF 6 are investigated. The relativistic embedding formalism introduced in this work is well suited for efficient modeling of open-shell systems containing late transition metal, lanthanide, and actinide molecular complexes.

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

Spin-state gaps and self-interaction-corrected density functional approximations: Octahedral Fe(II) complexes as case study

Accurate prediction of a spin-state energy difference is crucial for understanding the spin crossover phenomena and is very challenging for density functional approximations, especially for local and semi-local approximations due to delocalization errors. Here, we investigate the effect of the self-interaction error removal from the local spin density approximation (LSDA) and Perdew–Burke–Ernzerhof generalized gradient approximation on the spin-state gaps of Fe(II) complexes with various ligands using recently developed locally scaled self-interaction correction (LSIC) by Zope et al. [J. Chem. Phys. 151, 214108 (2019)]. The LSIC method is exact for one-electron density, recovers the uniform electron gas limit of the underlying functional, and approaches the well-known Perdew–Zunger self-interaction correction (PZSIC) as a particular case when the scaling factor is set to unity. Our results, when compared with reference diffusion Monte Carlo results, show that the PZSIC method significantly overestimates spin-state gaps favoring low spin states for all ligands and does not improve upon density functional approximations. The perturbative LSIC-LSDA using PZSIC densities significantly improves the gaps with a mean absolute error of 0.51 eV but slightly overcorrects for the stronger CO ligands. Finally, the quasi-self-consistent LSIC-LSDA, such as coupled-cluster single double and perturbative triple [CCSD(T)], gives a correct sign of spin-state gaps for all ligands with a mean absolute error of 0.56 eV, comparable to that of CCSD(T) (0.49 eV).

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

First discovery of an ultra-cool white dwarf benchmark in common proper motion with an M dwarf

Ultra-cool white dwarfs are among the oldest stellar remnants in the Universe. Their efficient gravitational settling and low effective temperatures are responsible for the smooth spectra they exhibit. For that reason, it is not possible to derive their radial velocities or to find the chemistry of the progenitors. The best that can be done is to infer such properties from associated sources, which are coeval. The simplest form of such a system is a common proper motion pair where one star is an evolved degenerate and the other a main-sequence star. Herein, we present the discovery of the first of such a system, the M dwarf LHS 6328 and the ultra-cool white dwarf PSO J1801+625, from the Pan-STARRS 1 3π survey and the Gaia Data Release 2. Follow-up spectra were collected covering a usable wavelength range of 3750–24 500 Å. Their spectra show that the white dwarf has an effective temperature of 3550 K and surface gravity of log $g$ = 7.45 ± 0.13 or log $g$ = 7.49 ± 0.13 for a CO or He core, respectively, when compared against synthetic spectra of ultra-cool white dwarf atmosphere models. The system has slightly subsolar metallicity with -0.25 < [Fe/H] < 0.0, and a spatial velocity of (U, V, W) = (-114.26 ± 0.24, 222.94 ± 0.60, 10.25 ± 0.34) km s -1 , the first radial velocity and metallicity measurements of an ultra-cool white dwarf. This makes it the first and only benchmark of its kind to date.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

High-resolution spectroscopy of neutral Yb atoms in a solid Ne matrix

Here, we present an experimental and theoretical study of the absorption and emission spectra of Yb atoms in a solid Ne matrix at a resolution of 0.025 nm. Five absorption bands were identified as due to transitions from the 4 f 14 5 d 0 6 s 2 1 S 0 ground-state configuration to 4 f 14 5 d 0 6 s 6 p and 4 f 13 5 d 1 6 s 2 configurations. The two lowest-energy bands were assigned to outer-shell transitions to 6 s 6 p 3 P 1 and 1 P 1 atomic states and displayed the structure of a broad doublet and an asymmetric triplet, respectively. The remaining three higher-frequency bands were assigned to inner-shell transitions to distinct J = 1 states arising from the 4 f 13 5 d 1 6 s 2 configuration and were highly structured with narrow linewidths. A classical simulation was performed to identify the stability and symmetry of possible trapping sites in the Ne crystal. It showed that the overarching 1 + 2 structure of the high-frequency bands could be predominantly ascribed to crystal-field splitting in the axial field of a 10-atom vacancy of C 4 v symmetry. Their prominent substructures were shown to be manifestations of phonon sidebands associated with the zero-phonon lines on each crystal-field state. Unprecedented for a metal–rare-gas system, resolution of individual phonon states on an allowed electronic transition was possible under excitation spectroscopy which reflects the semiquantum nature of solid Ne. In contrast to the absorption spectra, emission spectra produced by steady-state excitation into the 1 P 1 absorption band consisted of simple, unstructured fluorescence bands.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Three-dimensional stacking of canted antiferromagnetism and pseudospin current in undoped Sr 2 IrO 4 : Symmetry analysis and microscopic model realization

Recent optical second-harmonic generation experiments observed unexpected broken spatial symmetries in the undoped spin-orbit Mott insulator Sr2 IrO4, leading to intensive debates on the nature of its ground state. Here we propose that it is a canted antiferromagnetism (CAF) with a hidden order of circulating staggered pseudospin current. Symmetry analysis shows that a proper c-axis stacking of the CAF and the pseudospin current lead to a magnetoelectric coexistence state that breaks the twofold rotation, inversion, and time-reversal symmetries, consistent with experimental observations. We construct a three-dimensional Hubbard model with spin-orbit coupling and structural distortion for the five localized 5d Wannier orbitals centered at Ir sites and demonstrate the microscopic realization of the desired coexistence state in a wide range of band parameters via a combination of self-consistent Hartree-Fock and variational calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Delocalized polaron and Burstein-Moss shift induced by Li in α–V 2 O 5 : A DFT + DMFT study

For this work, we performed density functional theory (DFT)+U and dynamical mean field theory (DMFT) calculations with a continuous-time quantum Monte Carlo impurity solver to investigate the electronic properties of V 2 O 5 and Li x V 2 O 5 (x = 0.125 and 0.25). Pristine V 2 O 5 is a charge-transfer insulator with strong O p–V d hybridization, and it exhibits a large band gap (E gap ) as well as a nonzero conduction-band (CB) gap.We show that the band gap, the number of d electrons of vanadium, N d , and the CB gap for V 2 O 5 obtained from our DMFT calculations are in excellent agreement with the experimental values. While the DFT +U approach replicates the experimental band gap, it overestimates the value of N d and underestimates the CB gap. In the presence of low Li doping, the electronic properties of V 2 O 5 are mainly driven by a polaronic mechanism, and electron spin resonance and electron nuclear double resonance spectroscopies observed the coexistence of free and bound polarons. Notably, our DMFT results identify both polaron types, with the bound polaron being energetically preferred, while the DFT +U method only predicts the free polaron. Our DMFT analysis also reveals that increased Li doping leads to electron filling in the conduction band, shifting the Fermi level. This result is consistent with the observed Burstein-Moss shift upon enhanced Li doping, and we thus demonstrate that the DFT + DMFT approach can be used for an accurate and realistic description of strongly correlated materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Derivation of low-energy Hamiltonians for heavy-fermion materials

Here, by utilizing a multiorbital periodic Anderson model with parameters obtained from ab initio band structure calculations, combined with degenerate perturbation theory, we derive effective Kondo-Heisenberg and spin Hamiltonians that capture the interaction among the effective magnetic moments. This derivation encompasses fluctuations via both nonmagnetic 4⁢𝑓 0 and magnetic 4⁢𝑓 2 virtual states, and its accuracy is confirmed through comparison with experimental data obtained from CeIn 3 . The significant agreement observed between experimental results and theoretical predictions underscores the potential of deriving minimal models from first-principles calculations for achieving a quantitative description of 4⁢𝑓 materials. Moreover, our microscopic derivation unveils the underlying origin of anisotropy in the exchange interaction between Kramers doublets, shedding light on the conditions under which this anisotropy may be weak compared to the isotropic contribution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Spin-Orbit-Lattice Entangled State in A 2 ⁢MgReO 6 (A = Ca, Sr, Ba) Revealed by Resonant Inelastic X-Ray Scattering

The 5d 1 ordered double perovskites present an exotic playground for studying novel multipolar physics due to large spin-orbit coupling. Here, we present Re L 3 edge resonant inelastic Xray scattering (RIXS) results that reveal the presence of the dynamic Jahn-Teller effect in the A 2 MgReO 6 (A = Ca, Sr, Ba) family of 5d 1 double perovskites. The spin-orbit excitations in these materials show a strongly asymmetric lineshape and exhibit substantial temperature dependence, indicating that they are dressed with lattice vibrations. Our experimental results are explained quantitatively through a RIXS calculation based on a spin-orbit-lattice entangled electronic ground state with the dynamic Jahn-Teller effect taken into consideration. We find that the spin-orbitlattice entangled state is robust against magnetic and structural phase transitions as well as against significant static Jahn-Teller distortions. Our results illustrate the importance of including vibroniccoupling for a complete description of the ground state physics of 5d 1 double perovskites.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Effect of transport mechanism on the coarsening of bicontinuous structures: A comparison between bulk and surface diffusion

Here, coarsening of bicontinuous microstructures is observed in a variety of systems, such as nanoporous metals and mixtures that have undergone spinodal decomposition. To better understand the morphological evolution of these structures during coarsening, we compare the morphologies resulting from two different coarsening mechanisms, surface and bulk diffusion. We perform phase-field simulations of coarsening via each mechanism in a two-phase mixture at nominal volume fractions of 50%-50% and 36%-64%, and the simulated structures are characterized in terms of topology (genus density), the interfacial shape distribution, structure factor, and autocorrelations of phase and mean curvature. We observe self-similar evolution of morphology and topology and agreement with the expected power laws for dynamic scaling, in which the characteristic length scale increases over time proportionally to t 1/4 for surface diffusion and t 1/3 for bulk diffusion. While we observe the expected difference in the coarsening kinetics, we find that differences in self-similar morphology due to coarsening mechanism are relatively small, although typically they are larger at 36% volume fraction than at 50% volume fraction. In particular, we find that bicontinuous structures coarsened via surface diffusion have lower scaled genus densities than structures coarsened via bulk diffusion. We also compare the self-similar morphologies to those in literature and to two model bicontinuous structures, namely, constant-mean-curvature surfaces based on the Schoen G minimal surface and random leveled-wave structures. The average scaled mean curvatures of these model structures agree reasonably with those of the coarsened structures at both 36% and 50%, but we find substantial disagreements in the scaled genus densities and the standard deviations of mean curvature.

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 OSTI2020

Transmission of Images With Ultrasonic Elastic Shear Waves on a Metallic Pipe Using Amplitude Shift Keying Protocol

Transmission of information using ultrasonic elastic waves on existing metallic pipes provides an alternative communication option across physical barriers in a highly partitioned industrial complex, such as a nuclear facility. This work investigates the feasibility of the transmission of digital images over metallic pipes. Ultrasonic communication systems for transmission of images on a nuclear-grade stainless steel pipe were assembled for bench-scale demonstration. Information carriers in this system are refracted shear waves transmitted and received with piezoelectric transducers (PZTs) operating at 2-MHz nominal frequency. The refraction and propagation of ultrasonic shear waves were modeled with COMSOL software. An amplitude shift keying (ASK) communication protocol for image transmission was developed and implemented in the GNURadio software-defined radio (SDR) environment. Digital information was converted to analog ultrasonic signals using Red Pitaya electronic boards. The performance of the ASK protocol is evaluated at the output of every block in the GNURadio program by monitoring the transmission of select characters. Using the ASK communication protocol, the transmission of the 32-KB image was demonstrated at 2-Kbps bitrate across 6-ft-long stainless steel pipe. Finally, preliminary evaluation of ultrasonic communication on the piping of a nuclear facility, such as signal transmission on bent pipes, was performed with COMSOL computer simulations.

42 ENGINEERING↗
DOE OSTI2023

High-affinity amide-lanthanide adsorption to gram-positive soil bacteria

The gram-positive soil bacterium, Arthrobacter nicotianae, uses multiple organic acid functional groups to adsorb lanthanides onto its cell surface. At relevant soil pH conditions of 4.0–6.0, many of these functional groups are de-protonated and available for cation sorption and metal immobilization. However, among the plethora of naturally occurring site types, A. nicotianae is shown to possess high-affinity amide and phosphate sites that disproportionately affect lanthanide adsorption to the cell wall. We quantify neodymium (Nd)-selective site types, reporting an amide-Nd stability constant of log 10 K = 6.41 ± 0.23 that is comparable to sorption via phosphate-based moieties. These sites are two to three orders of magnitude more selective for Nd than the adsorption of divalent metals to ubiquitous carboxyl-based moieties. This implies the importance of lanthanide biosorption in the context of metal transport in subsurface systems despite trace concentrations of lanthanides found in the natural environment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Fabrication of Six Degrees-of-Freedom Hexflex Positioner With Integrated Strain Sensing Using Nonlithographically Based Microfabrication

In this study, a process flow is described for the low cost, flexible fabrication of metal micro-electromechanical systems (MEMS) with high performance integrated sensing. The process is capable of producing new designs in ≈1 week at an average unit cost of <$1 k/device even at batch sizes of ≈1–10, with expected sensing performance limits of about 135 dB over a 10 kHz sensor bandwidth. This is a ≈20× reduction in cost, ≈25× reduction in time, and potentially >30× increase in sensing dynamic range over comparable state-of-the-art compliant nanopositioners. The nonlithographically based microfabrication (NLBM) process is uniquely suited to create high performance nanopositioning architectures which are customizable to the positioning requirements of a range of nanoscale applications. These can significantly reduce the cost of nanomanufacturing research and development, as well as accelerate the development of new processes and the testing of fabrication process chains without excess capital investment. A six degrees-of-freedom (6DOF) flexural nanopositioner with integrated sensing for all 6DOF was fabricated using the newly developed process chain. The fabrication process was measured to have ≈30 μ m alignment. Sensor arm, flexure, and trace widths of 150 μ m, 150 μ m, and 800 μ m, respectively, were demonstrated. Process capabilities suggest lower bounds of 25 μ m, 50 μ m, and 100 μ m, respectively. Dynamic range sensing of 52 dB was demonstrated for the nanopositioner over a 10 kHz sensor bandwidth. Improvements are proposed to approach sensor performance of about 135 dB over a 10 kHz sensor bandwidth.

42 ENGINEERING↗
DOE OSTI2023

Nucleosynthesis and observation of the heaviest elements

Abstract The rapid neutron capture or ‘ r process’ of nucleosynthesis is believed to be responsible for the production of approximately half the natural abundance of heavy elements found on the periodic table above iron (with proton number $$Z=26$$ Z = 26 ) and all of the heavy elements above bismuth ( $$Z=83$$ Z = 83 ). In the course of creating the actinides and potentially superheavies, the r process must necessarily synthesize superheavy nuclei (those with extreme proton numbers, neutron numbers or both) far from isotopes accessible in the laboratory. Many questions about this process remain unanswered, such as ‘where in nature may this process occur?’ and ‘what are the heaviest species created by this process?’ In this review, we survey at a high level the nuclear properties relevant for the heaviest elements thought to be created in the r process. We provide a synopsis of the production and destruction mechanisms of these heavy species, in particular the actinides and superheavies, and discuss these heavy elements in relation to the astrophysical r process. We review the observational evidence of actinides found in the Solar system and in metal-poor stars and comment on the prospective of observing heavy-element production in explosive astrophysical events. Finally, we discuss the possibility that future observations and laboratory experiments will provide new information in understanding the production of the heaviest elements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗