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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on K2LaTa6(Br5O)3 by Materials Project

K2LaTa6(OBr5)3 crystallizes in the trigonal P-31c space group. The structure is three-dimensional. K is bonded in a 9-coordinate geometry to nine Br atoms. There are a spread of K–Br bond distances ranging from 3.65–3.85 Å. La is bonded in a distorted trigonal planar geometry to three equivalent O and six equivalent Br atoms. All La–O bond lengths are 2.54 Å. All La–Br bond lengths are 3.32 Å. Ta is bonded in a 1-coordinate geometry to one O and four Br atoms. The Ta–O bond length is 1.99 Å. There are a spread of Ta–Br bond distances ranging from 2.61–2.78 Å. O is bonded in a 3-coordinate geometry to one La and two equivalent Ta atoms. There are three inequivalent Br sites. In the first Br site, Br is bonded in a 4-coordinate geometry to two equivalent K, one La, and one Ta atom. In the second Br site, Br is bonded in a 2-coordinate geometry to two equivalent Ta atoms. In the third Br site, Br is bonded in a 3-coordinate geometry to one K and two equivalent Ta atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Transferable predictions of energetic and structural properties for refractory solid solution alloys across chemical compositions

We present a data-efficient approach to train graph neural networks (GNNs) on density functional theory (DFT) data for accurate and transferable predictions of energetic and structural properties of refractory solid solution alloys in the niobium-tantalum-vanadium (Nb-Ta-V) chemical space. We start by training the GNN model only on DFT data that describes refractory binary alloys niobium-tantalum (Nb-Ta), niobium-vanadium (Nb-V), and tantalum-vanadium (Ta-V) to predict formation enthalpy and root mean squared displacement. Once trained, the GNN predictions are tested on DFT data describing refractory ternary alloys Nb-Ta-V. While, unsurprisingly, direct transferability from binary to ternary is not sufficiently accurate, augmenting the training with only 1% of the available ternary data (uniformly distributed across the entire range of chemical compositions) improves significantly the quality of the GNN predictions. For comparison, we assess the transferability in the opposite direction by training GNN models on ternary Nb-Ta-V data and making predictions on binaries Nb-Ta, Nb-V, and Ta-V, which exhibits notably higher predictive errors. The proposed methodology, which favors transferability from lower-component to higher-component alloys, offers an efficient path towards avoiding the curse of dimensionality incurred when collecting DFT data for discovery and design of multi-component disordered alloys.

Density functional theory calculations↗
DOE OSTI2023

Minor titanium addition markedly improves the co-deformability of copper-tantalum composites

We investigated the microstructures of equal channel angular extrusion (ECAE) processed sintered composites of copper (Cu) and tantalum (Ta). These composites were produced with nominal Ta volume percentages ranging from 25% to 75%. Additional composites of the same nominal Ta content were prepared with a minor amount of titanium (Ti) added to facilitate interphase bonding. Ti addition was found to markedly improve the strength and co-deformability of the composites, allowing reliable extrusion of Cu-Ta composites with novel microstructures. A major influence of the Ti appears to be to soften the Ta, which contributes to improved co-deformability by reducing the flow stress mismatch between the composite constituents. Here, a change in the fracture surface morphology in the Ti-modified composite compared to the unmodified composite suggests that the Ti may also improve cohesion between Cu and Ta by reducing Ta surface oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Cationic Tantalum Hydrides Catalyze Hydrogenolysis and Alkane Metathesis Reactions of Paraffins and Polyethylene

Sulfated aluminum oxide (SAO), a high surface area material containing sulfate anions that behave like weakly coordinating anions, reacts with Ta(=CH t Bu)(CH 2 t Bu) 3 to form [Ta(CH 2 t Bu) 2 (O–) 2 ][SAO] (1). Subsequent treatment with H 2 forms Ta–H + sites supported on SAO that are active in hydrogenolysis and alkane metathesis reactions. In both reactions Ta–H + is more active than related neutral Ta–H sites supported on silica. This reaction chemistry extends to melts of high-density polyethylene (HDPE), where Ta–H + converts 30% of a low molecular weight HDPE (M n = 2.5 kg mol –1 ; D = 3.6) to low molecular weight paraffins under hydrogenolysis conditions. Under alkane metathesis conditions Ta–H + converts this HDPE to a high MW fraction (M n = 6.2 kDa; D = 2.3) and low molecular weight alkane products (C 13 –C 32 ). Furthermore, these results show that incorporating charge as a design element in supported d 0 metal hydrides is a viable strategy to increase the reaction rate in challenging reactions involving reorganization of C–C bonds in alkanes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Hiding in plain sight: The prevalence and impact of trions and Fermi polarons in transient absorption spectroscopy experiments of 2D semiconductors

Transient absorption (TA) spectroscopy is one of the most popular experimental methods to measure the excited state lifetimes and charge carrier recombination mechanisms in two dimensional (2D) semiconductors. This fundamental information is essential for designing and optimizing the next generation of ultrathin and lightweight 2D semiconductor-based optoelectronic devices. However, the interpretation of TA spectroscopy data varies across the community. The community lacks a unifying physical explanation for how and why experimental variables such as incident light intensity, sample-substrate interactions, and/or applied bias affect TA spectral data. This Perspective (1) compares the physical chemistry TA literature to nanomaterial physics literature from a historical perspective, (2) reviews multiple physical explanations that the TA community developed to explain spectral features and experimental trends, (3) provides a unifying explanation for how and why trions—and, more generally, Fermi polarons—contribute to TA spectra, and (4) quantifies the extent to which various physical interpretations and data analysis procedures yield different timescales and mechanisms for the same set of experimental results. We highlight the importance of considering trions/Fermi polarons in TA measurements and their implications for advancing our understanding of 2D material properties.

2D materials↗
DOE OSTI2022

Local Group timing argument and virial theorem mass estimators from cosmological simulations

ABSTRACT We identify Local Group (LG) analogues in the IllustrisTNG cosmological simulation, and use these to study two-mass estimators for the LG: One based on the timing argument (TA) and one based on the virial theorem (VT). Including updated measurements of the Milky Way-M31 tangential velocity and the cosmological constant, we show that the TA mass estimator slightly overestimates the true median LG-mass, though the ratio of the TA to the true mass is consistent at the approximate 90 per cent c.l.. These are in broad agreement with previous results using dark matter-only simulations. We show that the VT estimator better estimates the true LG-mass, though there is a larger scatter in the virial mass to true mass ratio relative to the corresponding ratio for the TA. We attribute the broader scatter in the VT estimator to several factors, including the predominantly radial orbits for LG satellite galaxies, which differs from the VT assumption of isotropic orbits. With the systematic uncertainties we derive, the updated measurements of the LG mass at 90 per cent c.l. are $4.75_{-2.41}^{+2.22} \times 10^{12}$ M⊙ from the TA and $2.0_{-1.5}^{+2.1} \times 10^{12}$ M⊙ from the VT. We consider the LMC’s effect on the TA and VT LG mass estimates, and do not find exact LMC–MW–M31 analogues in the Illustris simulations. However, in LG simulations with satellite companions as massive as the LMC, we find that the effect on the TA and VT estimators is small, though we need further studies on a larger sample of LMC–MW–M31 systems to confirm these results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Toxin-Antitoxin Systems Reflect Community Interactions Through Horizontal Gene Transfer

Bacterial evolution through horizontal gene transfer (HGT) reflects their community interactions. In this way, HGT networks do well at mapping community interactions, but offer little toward controlling them—an important step in the translation of synthetic strains into natural contexts. Toxin–antitoxin (TA) systems serve as ubiquitous and diverse agents of selection; however, their utility is limited by their erratic distribution in hosts. Here we examine the heterogeneous distribution of TAs as a consequence of their mobility. By systematically mapping TA systems across a 10,000 plasmid network, we find HGT communities have unique and predictable TA signatures. We propose these TA signatures arise from plasmid competition and have further potential to signal the degree to which plasmids, hosts, and phage interact. To emphasize these relationships, we construct an HGT network based solely on TA similarity, framing specific selection markers in the broader context of bacterial communities. This work both clarifies the evolution of TA systems and unlocks a common framework for manipulating community interactions through TA compatibility.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

LANL Meteorological Program: 2020 Data Completeness/Quality Report

Los Alamos National Laboratory (LANL) operates four mesa-top meteorology towers: Technical Area (TA) 06, TA-49, TA-53, and TA-54. An additional tower is located in Mortandad Canyon (TA-5 MDCN), and a rain gauge at North Community (NCOM). A description of the meteorology monitoring network is found in Dewart and Boggs (2014). Mesa-top towers are instrumented at 1.2 meters (m), 11.5 m, 23 m, and 46 m. In addition, TA-06 is instrumented at 92 m. The TA-5 MDCN tower is 10 m in height and is instrumented at 1.2 m and 10 m. Data are collected every 15 minutes. Range checking is done on each measurement every 15 minutes; data that are beyond normal ranges are eliminated from the data set and replaced by a code for missing data. In addition, data are reviewed weekly by meteorologists to identify bad data not identified by range checking. The data steward eliminates these data from the data set and replaces them with a code for missing data. The instrument technicians also review that data and schedule instrument replacement as required. Data completeness is determined by the number of total 15-minute records available versus the total number of possible measurements for the entire year. As a rule, the meteorologists do not attempt to estimate data that are eliminated as bad data. Original datalogger records, containing bad data, can be recalled from program archival storage.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Quasi-static to Dynamic Mechanical Response and Microstructure Development of Tantalum-Tungsten Alloys

Lawrence Livermore National Laboratory (LLNL) is interested the quasi-static to dynamic mechanical response and microstructure evolution of tantalum-tungsten (Ta-W) alloys (Ta-2.5W, Ta-5W, and Ta-10W, wt.%) made by conventional wrought processing and additive manufacturing (AM). This work scope was performed at the Colorado School of Mines (Mines) and included quasi-static (e.g., 10 -3 s -1 ) mechanical testing in tension and compression, along with selected high strain rate (Kolsky) pressure bar testing in compression (e.g., 10 3 s -1 ), with and without temperature variations in some instances. Complementary microstructure characterization was performed on undeformed and deformed samples to understand the role of processing on microstructural evolution and the deformation mechanisms that impact the mechanical response with variations in strain rate, temperature, and strain state (e.g., tension versus compression in selected examples). The wrought material provided by LLNL from Viridis Materials was found to have unrecrystallized regions within the microstructure, which led to unexpected results relative to previously reported properties for Ta-W. The AM Ta-2.5W (wt.%) material provided by LLNL was found to have higher compressive strength than wrought Ta-2.5W (wt.%), which is hypothesized to be due to differences in the crystallographic texture between the two materials. This project partially supported several postdocs and graduate students at Mines.

36 MATERIALS SCIENCE↗
DOE OSTI2024

An Investigation of Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating

Recent progress has seen multiple Ta 2 O 5 polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta 2 O 5 particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an 18 O 2 atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta 2 O 5 phase or a similar, but not identical, crystalline β-Ta 2 O 5 phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic “H-Ta 2 O 5 ” phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta 2 O 5 . Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta 2 O 5 . We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta2Be by Materials Project

BeTa2 is Khatyrkite structured and crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Be is bonded in a distorted q6 geometry to two equivalent Be and eight equivalent Ta atoms. Both Be–Be bond lengths are 2.45 Å. All Be–Ta bond lengths are 2.58 Å. Ta is bonded in a 4-coordinate geometry to four equivalent Be and one Ta atom. The Ta–Ta bond length is 2.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta3Co3C by Materials Project

Ta3Co3C crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Ta is bonded in a 2-coordinate geometry to six Co and two equivalent C atoms. There are a spread of Ta–Co bond distances ranging from 2.75–2.83 Å. Both Ta–C bond lengths are 2.16 Å. There are two inequivalent Co sites. In the first Co site, Co is bonded in a distorted q6 geometry to six equivalent Ta and six Co atoms. There are three shorter (2.42 Å) and three longer (2.52 Å) Co–Co bond lengths. In the second Co site, Co is bonded to six equivalent Ta and six equivalent Co atoms to form CoTa6Co6 cuboctahedra that share edges with six equivalent CTa6 octahedra and faces with six equivalent CoTa6Co6 cuboctahedra. C is bonded to six equivalent Ta atoms to form CTa6 octahedra that share corners with six equivalent CTa6 octahedra and edges with six equivalent CoTa6Co6 cuboctahedra. The corner-sharing octahedral tilt angles are 45°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaCo2 by Materials Project

Co2Ta is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Ta is bonded in a 12-coordinate geometry to four equivalent Ta and twelve equivalent Co atoms. All Ta–Ta bond lengths are 2.91 Å. All Ta–Co bond lengths are 2.79 Å. Co is bonded to six equivalent Ta and six equivalent Co atoms to form a mixture of edge, face, and corner-sharing CoTa6Co6 cuboctahedra. All Co–Co bond lengths are 2.38 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaCr2 by Materials Project

Cr2Ta is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Ta is bonded in a 12-coordinate geometry to four equivalent Ta and twelve equivalent Cr atoms. All Ta–Ta bond lengths are 3.00 Å. All Ta–Cr bond lengths are 2.88 Å. Cr is bonded to six equivalent Ta and six equivalent Cr atoms to form a mixture of face, edge, and corner-sharing CrTa6Cr6 cuboctahedra. All Cr–Cr bond lengths are 2.45 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TaBe2 by Materials Project

Be2Ta is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Be is bonded to six equivalent Be and six equivalent Ta atoms to form a mixture of face, edge, and corner-sharing BeTa6Be6 cuboctahedra. All Be–Be bond lengths are 2.31 Å. All Be–Ta bond lengths are 2.70 Å. Ta is bonded in a 12-coordinate geometry to twelve equivalent Be and four equivalent Ta atoms. All Ta–Ta bond lengths are 2.82 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta3Sn by Materials Project

Ta3Sn crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. Ta is bonded in a 6-coordinate geometry to two equivalent Ta and four equivalent Sn atoms. Both Ta–Ta bond lengths are 2.66 Å. All Ta–Sn bond lengths are 2.98 Å. Sn is bonded to twelve equivalent Ta atoms to form a mixture of face and edge-sharing SnTa12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta6Si7Ni16 by Materials Project

Ta6Ni16Si7 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ta is bonded in a 12-coordinate geometry to eight Ni and four equivalent Si atoms. There are four shorter (2.69 Å) and four longer (2.75 Å) Ta–Ni bond lengths. All Ta–Si bond lengths are 2.86 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 12-coordinate geometry to three equivalent Ta, six Ni, and three equivalent Si atoms. There are three shorter (2.56 Å) and three longer (2.63 Å) Ni–Ni bond lengths. All Ni–Si bond lengths are 2.29 Å. In the second Ni site, Ni is bonded in a 7-coordinate geometry to three equivalent Ta, six Ni, and four Si atoms. All Ni–Ni bond lengths are 2.62 Å. There are one shorter (2.27 Å) and three longer (2.49 Å) Ni–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded in a body-centered cubic geometry to eight equivalent Ni atoms. In the second Si site, Si is bonded to four equivalent Ta and eight Ni atoms to form a mixture of corner and face-sharing SiTa4Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ta3SiTe6 by Materials Project

Ta3SiTe6 crystallizes in the orthorhombic Pnma space group. The structure is two-dimensional and consists of two Ta3SiTe6 sheets oriented in the (0, 0, 1) direction. there are three inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to one Si4- and six Te+1.83- atoms to form distorted TaSiTe6 pentagonal bipyramids that share an edgeedge with one SiTa4Te4 hexagonal bipyramid, edges with four TaSiTe6 pentagonal bipyramids, and a faceface with one TaSiTe6 pentagonal bipyramid. The Ta–Si bond length is 2.84 Å. There are a spread of Ta–Te bond distances ranging from 2.80–2.88 Å. In the second Ta5+ site, Ta5+ is bonded in a 8-coordinate geometry to two equivalent Si4- and six Te+1.83- atoms. There are one shorter (2.83 Å) and one longer (2.84 Å) Ta–Si bond lengths. There are a spread of Ta–Te bond distances ranging from 2.83–2.95 Å. In the third Ta5+ site, Ta5+ is bonded to one Si4- and six Te+1.83- atoms to form distorted TaSiTe6 pentagonal bipyramids that share edges with two equivalent SiTa4Te4 hexagonal bipyramids, edges with two equivalent TaSiTe6 pentagonal bipyramids, and a faceface with one TaSiTe6 pentagonal bipyramid. The Ta–Si bond length is 2.73 Å. There are a spread of Ta–Te bond distances ranging from 2.76–2.96 Å. Si4- is bonded to four Ta5+ and four Te+1.83- atoms to form distorted SiTa4Te4 hexagonal bipyramids that share corners with two equivalent SiTa4Te4 hexagonal bipyramids and edges with three TaSiTe6 pentagonal bipyramids. There are two shorter (2.71 Å) and two longer (2.76 Å) Si–Te bond lengths. There are three inequivalent Te+1.83- sites. In the first Te+1.83- site, Te+1.83- is bonded in a 3-coordinate geometry to three Ta5+ atoms. In the second Te+1.83- site, Te+1.83- is bonded in a 4-coordinate geometry to three Ta5+ and one Si4- atom. In the third Te+1.83- site, Te+1.83- is bonded in a 4-coordinate geometry to three Ta5+ and one Si4- atom.

36 MATERIALS SCIENCE↗