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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Pr3Lu by Materials Project

LuPr3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Lu is bonded to twelve equivalent Pr atoms to form LuPr12 cuboctahedra that share corners with six equivalent LuPr12 cuboctahedra, corners with twelve equivalent PrPr8Lu4 cuboctahedra, edges with eighteen equivalent PrPr8Lu4 cuboctahedra, faces with eight equivalent LuPr12 cuboctahedra, and faces with twelve equivalent PrPr8Lu4 cuboctahedra. There are six shorter (3.65 Å) and six longer (3.67 Å) Lu–Pr bond lengths. Pr is bonded to four equivalent Lu and eight equivalent Pr atoms to form PrPr8Lu4 cuboctahedra that share corners with four equivalent LuPr12 cuboctahedra, corners with fourteen equivalent PrPr8Lu4 cuboctahedra, edges with six equivalent LuPr12 cuboctahedra, edges with twelve equivalent PrPr8Lu4 cuboctahedra, faces with four equivalent LuPr12 cuboctahedra, and faces with sixteen equivalent PrPr8Lu4 cuboctahedra. There are a spread of Pr–Pr bond distances ranging from 3.63–3.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbLuIr2 by Materials Project

LuTbIr2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Lu is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Lu–Ir bond lengths are 2.95 Å. Tb is bonded in a body-centered cubic geometry to eight equivalent Ir atoms. All Tb–Ir bond lengths are 2.95 Å. Ir is bonded in a body-centered cubic geometry to four equivalent Lu and four equivalent Tb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LuVO2 by Materials Project

LuVO2 crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Lu is bonded to six equivalent O atoms to form edge-sharing LuO6 octahedra. There are four shorter (2.27 Å) and two longer (2.28 Å) Lu–O bond lengths. V is bonded in a square co-planar geometry to four equivalent O atoms. All V–O bond lengths are 2.20 Å. O is bonded to three equivalent Lu and two equivalent V atoms to form a mixture of distorted corner and edge-sharing OLu3V2 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on DyLuTl2 by Materials Project

LuDyTl2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Lu is bonded in a body-centered cubic geometry to eight equivalent Tl atoms. All Lu–Tl bond lengths are 3.26 Å. Dy is bonded in a body-centered cubic geometry to eight equivalent Tl atoms. All Dy–Tl bond lengths are 3.26 Å. Tl is bonded in a body-centered cubic geometry to four equivalent Lu and four equivalent Dy atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiLuIn2 by Materials Project

LiLuIn2 is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Li is bonded in a body-centered cubic geometry to eight equivalent In atoms. All Li–In bond lengths are 3.12 Å. Lu is bonded in a body-centered cubic geometry to eight equivalent In atoms. All Lu–In bond lengths are 3.12 Å. In is bonded in a body-centered cubic geometry to four equivalent Li and four equivalent Lu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The Role of Asparagine as a Gatekeeper Residue in the Selective Binding of Rare Earth Elements by Lanthanide‐Binding Peptides

Abstract Lanthanide‐binding tag (LBT) peptides selectively complex lanthanide cations (Ln 3+ ) in their binding pockets and are promising for lanthanide separation. However, designing LBTs that selectively target specific Ln 3+ cations remains a challenge due to limited molecular‐level understanding and control of interactions within the lanthanide‐binding pocket. In this study, we reveal that the N5 asparagine residue acts as a gatekeeper in the binding pocket, resulting in a 100‐fold selectivity for smaller Lu 3+ over larger La 3+ cations. Nuclear magnetic resonance spectroscopy and molecular dynamics simulations show that the N5 residue weakly binds to the larger La 3+ cation, permitting H 2 O molecules inside the pocket. For the smaller Lu 3+ cations, the N5 residue forms an inter‐arm hydrogen bond with the E14 glutamic acid residue, locking the Lu 3+ cation in the pocket and preventing H 2 O infiltration. Mutating the N5 asparagine to a D5 aspartic acid prevents such a hydrogen bond, eliminating the gatekeeping mechanism and precipitously reducing selectivity. The resulting binding affinity to Ln 3+ cations is non‐monotonic but generally increases with cation size. These results suggest a molecular design paradigm: the reduced affinity for larger lanthanides is due to open pocket conformations, while the selectivity of smaller Ln 3+ cations over larger ones is due to the gatekeeping hydrogen bond.

Chemistry↗
DOE OSTI2021

Interplay of physically different properties leading to challenges in separating lanthanide cations – an ab initio molecular dynamics and experimental study

Lanthanide elements have well-documented similarities in their chemical behavior, which make the valuable trivalent lanthanide cations (Ln 3+ ) particularly difficult to separate from each other in water. Here, we apply ab initio molecular dynamics simulations to compare the free energies (Δ G ads ) associated with the adsorption of lanthanide cations to silica surfaces at a pH condition where SiO – groups are present. The predicted Δ G ads for lutetium (Lu 3+ ) and europium (Eu 3+ ) are similar within statistical uncertainties; this is in qualitative agreement with our batch adsorption measurements on silica. This finding is remarkable because the two cations exhibit hydration free energies (Δ G hyd ) that differ by >2 eV, different hydration numbers, and different hydrolysis behavior far from silica surfaces. We observe that the similarity in Lu 3+ and Eu 3+ Δ G ads is the result of a delicate cancellation between the difference in Eu 3+ and Lu 3+ hydration (Δ G hyd ), and their difference in binding energies to silica. We propose that disrupting this cancellation at the two end points, either for adsorbed or completely desorbed lanthanides ( e.g. , via nanoconfinment or mixed solvents), will lead to effective Ln 3+ separation.

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

Metadynamics investigation of lanthanide solvation free energy landscapes and insights into separations energetics

Lanthanide ion solvation chemistry in nonaqueous phases is key to understanding and developing effective separation processes for these critical materials. Due to the complexity and inherent disorder of the solution phase, a comprehensive picture of the solvated metal ion is often difficult to generate solely from conventional spectroscopic approaches and electronic structure calculations, particularly in the extractant phase. In this work, we use classical molecular dynamics (MD) simulation with an advanced sampling technique, metadynamics, supplemented by experimental spectroscopy and speciation analysis, to measure lanthanide solvation free energy landscapes. We define coordination-based collective variables to probe the entire range of solvation configurations in the organic phase of lanthanum (La), europium (Eu), and lutetium (Lu) nitrate salts bound with a commonly used extractant, N,N′-dimethyl, N,N′-dioctylhexylethoxymalonamide (DMDOHEMA). The known lanthanide extraction trend of La ≈ Eu > Lu is readily explained by the measured free energy surfaces, which show consistent DMDOHEMA coordination from La to Eu, followed by loss of DMDOHEMA coordination from Eu to Lu. These simulations suggest how ligand crowding at the metal center can control selectivity, in this case resulting in the opposite extraction trend as observed with other conventional extractants, where the enthalpic contribution from increasing lanthanide charge density across the series dominates the extraction energetics. We also find that the presence of inner-sphere water, verified by time-resolved fluorescence, diversifies the accessible solvation structures. As a result, understanding solvation requires consideration of an entire thermodynamic ensemble, rather than the single dominant lowest-energy structure, as is often considered out of necessity in interpretation of spectroscopic data or in electronic structure-based ligand design approaches. In general, we demonstrate how metadynamics uniquely enables investigation of complex, multidimensional solvation energetic landscapes, and how it can explain selectivity trends where extraction is controlled by more complex mechanisms than simple charge density-based selectivity.

Wang, Xiaoyu↗
DOE OSTI2024

Stabilization of reactive rare earth alkyl complexes through mechanistic studies

Rare earth tris(alkyl) complexes such as M(CH 2 SiMe 3 ) 3 (sol) n are widely used as precursors for many compounds and as homogeneous catalysts for alkene polymerization and alkane functionalization. However, the thermal instability of those most conveniently made from the commercially available lithium salt of the neosilyl anion, LiCH 2 SiMe 3 , Li(r), restricts their utility. We present a new range of synthetically useful, more kinetically stable rare earth neosilyl solvates, derived from a full kinetic study of the various possible decomposition mechanisms of 7 known and 12 new solvated rare earth neosilyl complexes M(CH 2 SiMe 3 ) 3 (sol) n M = Sc(III), Y(III), Lu(III), Sm(III), and sol = THF; TMEDA; DMPE; diglyme ((CH 3 ) 2 (OCH 2 CH 2 ) 2 O, G 2 ), triglyme ((CH 3 ) 2 (OCH 2 CH 2 ) 3 O, G 3 ). Surprisingly, simply using higher-denticity donors to sterically disfavor neosilyl γ-H elimination is not effective. While Sc(r) 3 ((CH 3 ) 2 (OCH 2 CH 2 ) 2 O) has a half-life, t 1/2 , of 258.1 h, six times longer than for Sc(r) 3 (C 4 H 8 O) 2 (t 1/2 = 43 h), Lu(r) 3 ((CH 3 ) 2 (OCH 2 CH 2 ) 2 O) and Y(r) 3 ((CH 3 ) 2 (OCH 2 CH 2 ) 2 O) do not show the expected, analogous increased t 1/2 . This is because new decomposition pathways appear for poorly fitting donors. Finally, kinetic studies demonstrate the impact of small, and increasing amounts of LiCl on the kinetics of the reactivity of the smaller alkyls Y(r) 3 (THF) 2 and Lu(r) 3 (THF) 2 ; molecules used in hydrocarbon chemistry and catalysis for fifty years. A new route to pure Y(r) 3 (THF) 2 , which avoids the traditional use of Li(r), is presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Completion of lunar magma ocean solidification at 4.43 Ga

Crystallization of the lunar magma ocean yielded a chemically unique liquid residuum named KREEP. This component is expressed as a large patch on the near side of the Moon and a possible smaller patch in the northwest portion of the Moon’s South Pole-Aitken basin on the far side. Thermal models estimate that the crystallization of the lunar magma ocean (LMO) could have spanned from 10 and 200 My, while studies of radioactive decay systems have yielded inconsistent ages for the completion of LMO crystallization covering over 160 My. Here, we show that the Moon achieved >99% crystallization at 4,429 ± 76 Ma, indicating a lunar formation age of ~4,450 Ma or possibly older. Using the 176 Lu– 176 Hf decay system (t 1/2 = 37 Gy), we found that the initial 176 Hf/ 177 Hf ratios of lunar zircons with varied U–Pb ages are consistent with their crystallization from a KREEP-rich reservoir with a consistently low 176 Lu/ 177 Hf ratio of 0.0167 that emerged ~140 My after solar system formation. The previously proposed younger model age of ~4.33 Ga for the source of mare basalts (240 My after solar system formation) might reflect the timing of a large impact. Our results demonstrate that lunar magma ocean crystallization took place while the Moon was still battered by planetary embryos and planetesimals leftover from the main stage of planetary accretion. The study of Lu–Hf model ages for samples brought back from the South Pole-Aitken basin will help to assess the lateral continuity of KREEP and further understand its significance in the early history of the Moon.

Science & Technology - Other Topics↗
DOE OSTI2022

Development of Chemical Procedures for Isotope Harvesting: Separation of Trace Hafnium from Tungsten

The separation of trace hafnium from bulk tungsten alloys is of interest for isotope harvesting at the National Superconducting Cyclotron Laboratory and the Facility for Rare Ion Beams because 172 Hf, the parent of 172 Lu, accumulates in tungsten alloy beam blockers at these facilities. In this work, a procedure for the separation of trace hafnium from a bulk tungsten alloy (454 g) was established using tracer isotopes ( 175 Hf, 88 Zr, 173 Lu, and 88 Y). Here, the procedure employed dissolution in an HF–HNO 3 solution followed by a calcium fluoride precipitation, and then extraction chromatography was used for more selective separation steps. Two stages of column separations using LN resin (HDEHP based) and TRU resin (CMPO based) were performed. Gamma-ray spectroscopy and mass spectrometry were used to analyze the final hafnium sample and follow the steps in the chemical processing. Furthermore, the final recovery of hafnium was high (90 ± 8)%, and the mass of tungsten and other transition metals was reduced to near background levels (as determined by ICP-MS of the blank acid solutions). Zirconium follows hafnium quantitatively in this procedure; there was no detectable 173 Lu in the final hafnium sample.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Extraction of Beam-Spin Asymmetries from the Hard Exclusive π + Channel off Protons in a Wide Range of Kinematics

We have measured beam-spin asymmetries to extract the $\sin\phi$ moment $A_{LU}^{\sin\phi}$ from the hard exclusive $\vec{e} p \to e^\prime n \pi^+$ reaction above the resonance region, for the first time with nearly full coverage from forward to backward angles in the center-of-mass. The $A_{LU}^{\sin\phi}$ moment has been measured up to 6.6 GeV$^{2}$ in $-t$, covering the kinematic regimes of Generalized Parton Distributions (GPD) and baryon-to-meson Transition Distribution Amplitudes (TDA) at the same time. The experimental results in very forward kinematics demonstrate the sensitivity to chiral-odd and chiral-even GPDs. In very backward kinematics where the TDA framework is applicable, we found $A_{LU}^{\sin\phi}$ to be negative, while a sign change was observed near 90$^\circ$ in the center-of-mass. The unique results presented in this paper will provide critical constraints to establish reaction mechanisms that can help to further develop the GPD and TDA frameworks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Combining Sparse Approximate Factorizations with Mixed-precision Iterative Refinement

The standard LU factorization-based solution process for linear systems can be enhanced in speed or accuracy by employing mixed-precision iterative refinement. Most recent work has focused on dense systems. We investigate the potential of mixed-precision iterative refinement to enhance methods for sparse systems based on approximate sparse factorizations. In doing so, we first develop a new error analysis for LU- and GMRES-based iterative refinement under a general model of LU factorization that accounts for the approximation methods typically used by modern sparse solvers, such as low-rank approximations or relaxed pivoting strategies. We then provide a detailed performance analysis of both the execution time and memory consumption of different algorithms, based on a selected set of iterative refinement variants and approximate sparse factorizations. Our performance study uses the multifrontal solver MUMPS, which can exploit block low-rank factorization and static pivoting. We evaluate the performance of the algorithms on large, sparse problems coming from a variety of real-life and industrial applications showing that mixed-precision iterative refinement combined with approximate sparse factorization can lead to considerable reductions of both the time and memory consumption.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Materials Data on Lu2SO2 by Materials Project

Lu2O2S crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Lu3+ is bonded in a 4-coordinate geometry to three equivalent S2- and four equivalent O2- atoms. All Lu–S bond lengths are 2.82 Å. There are three shorter (2.21 Å) and one longer (2.24 Å) Lu–O bond lengths. S2- is bonded to six equivalent Lu3+ atoms to form distorted SLu6 octahedra that share corners with twelve equivalent OLu4 tetrahedra, edges with six equivalent SLu6 octahedra, and edges with six equivalent OLu4 tetrahedra. O2- is bonded to four equivalent Lu3+ atoms to form OLu4 tetrahedra that share corners with six equivalent SLu6 octahedra, corners with six equivalent OLu4 tetrahedra, edges with three equivalent SLu6 octahedra, and edges with three equivalent OLu4 tetrahedra. The corner-sharing octahedra tilt angles range from 26–49°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LuPPt by Materials Project

LuPtP is hexagonal omega structure-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Lu3+ is bonded to six equivalent Pt2- and six equivalent P1- atoms to form a mixture of edge and face-sharing LuP6Pt6 cuboctahedra. All Lu–Pt bond lengths are 3.03 Å. All Lu–P bond lengths are 3.03 Å. Pt2- is bonded in a 9-coordinate geometry to six equivalent Lu3+ and three equivalent P1- atoms. All Pt–P bond lengths are 2.37 Å. P1- is bonded in a 9-coordinate geometry to six equivalent Lu3+ and three equivalent Pt2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LuSbPt by Materials Project

PtLuSb is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Lu3+ is bonded to four equivalent Pt2- and six equivalent Sb1- atoms to form a mixture of distorted corner and face-sharing LuSb6Pt4 tetrahedra. All Lu–Pt bond lengths are 2.83 Å. All Lu–Sb bond lengths are 3.27 Å. Pt2- is bonded in a body-centered cubic geometry to four equivalent Lu3+ and four equivalent Sb1- atoms. All Pt–Sb bond lengths are 2.83 Å. Sb1- is bonded in a 10-coordinate geometry to six equivalent Lu3+ and four equivalent Pt2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Lu3BC3 by Materials Project

Lu3BC3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Lu3+ sites. In the first Lu3+ site, Lu3+ is bonded to five C4- atoms to form LuC5 square pyramids that share corners with five equivalent LuC5 square pyramids, edges with four equivalent LuC6 octahedra, and edges with four equivalent LuC5 square pyramids. There are a spread of Lu–C bond distances ranging from 2.29–2.58 Å. In the second Lu3+ site, Lu3+ is bonded to six C4- atoms to form LuC6 octahedra that share corners with four equivalent LuC6 octahedra, edges with four equivalent LuC6 octahedra, and edges with eight equivalent LuC5 square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. There are a spread of Lu–C bond distances ranging from 2.47–2.55 Å. B3+ is bonded in a linear geometry to two equivalent C4- atoms. Both B–C bond lengths are 1.46 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded in a 6-coordinate geometry to five Lu3+ and one B3+ atom. In the second C4- site, C4- is bonded to six Lu3+ atoms to form a mixture of edge and corner-sharing CLu6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°.

36 MATERIALS SCIENCE↗