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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Isomerization and Selective Hydrogenation of Propyne: Screening of Metal–Organic Frameworks Modified by Atomic Layer Deposition

Various metal oxide clusters upward of 8 atoms (Cu, Cd, Co, Fe, Ga, Mn, Mo, Ni, Sn, W, Zn, In, and Al) were incorporated into the pores of the metal–organic framework (MOF) NU-1000 via atomic layer deposition (ALD) and tested via high-throughput screening for catalytic isomerization and selective hydrogenation of propyne. Cu and Co were found to be the most active for propyne hydrogenation to propylene, and synergistic bimetallic combinations of Co and Zn, along with standalone Zn and Cd, were established as the most active for conversion to the isomerized product, propadiene. The combination of Co and Zn in NU-1000 diminished the propensity for full hydrogenation to propane as well as coking compared to its individual components. Finally, this study highlights the potential for high-throughput screening to survey monometallic and bimetallic cluster combinations that best affect the efficient transformation of small molecules, while discerning mechanistic differences in isomerization and hydrogenation by different metals.

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

High‐Spin and Reactive Fe 13 Cluster with Exposed Metal Sites

Abstract Atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp* 4 W 4 Fe 13 S 12 , displaying a Fe 13 core with M−M bonds that has precedent only in main group and late metal chemistry. M 13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp* 4 W 4 Fe 13 S 12 displays a large spin ground state of S =13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.

Scott, Anna G.↗
NASA NTRS1972

Upper limits on the atomic hydrogen abundance in 12 globular clusters.

Description of 21-cm neutral-hydrogen line observations of 12 globular clusters performed with negative results by means of the NRAO 140-ft telescope. Limits on the atomic hydrogen content yielded by these observations over a range of 11 to 85 solar masses are presented.-

Kerr, F. J.↗
NASA NTRS2004

Chemical Reaction and Flow Modeling in Fullerene and Nanotube Production

The development of processes to produce fullerenes and carbon nanotubes has largely been empirical. Fullerenes were first discovered in the soot produced by laser ablation of graphite [1]and then in the soot of electric arc evaporated carbon. Techniques and conditions for producing larger and larger quantities of fullerenes depended mainly on trial and error empirical variations of these processes, with attempts to scale them up by using larger electrodes and targets and higher power. Various concepts of how fullerenes and carbon nanotubes were formed were put forth, but very little was done based on chemical kinetics of the reactions. This was mainly due to the complex mixture of species and complex nature of conditions in the reactors. Temperatures in the reactors varied from several thousand degrees Kelvin down to near room temperature. There are hundreds of species possible, ranging from atomic carbon to large clusters of carbonaceous soot, and metallic catalyst atoms to metal clusters, to complexes of metals and carbon. Most of the chemical kinetics of the reactions and the thermodynamic properties of clusters and complexes have only been approximated. In addition, flow conditions in the reactors are transient or unsteady, and three dimensional, with steep spatial gradients of temperature and species concentrations. All these factors make computational simulations of reactors very complex and challenging. This article addresses the development of the chemical reaction involved in fullerene production and extends this to production of carbon nanotubes by the laser ablation/oven process and by the electric arc evaporation process. In addition, the high-pressure carbon monoxide (HiPco) process is discussed. The article is in several parts. The first one addresses the thermochemical aspects of modeling; and considers the development of chemical rate equations, estimates of reaction rates, and thermodynamic properties where they are available. The second part addresses modeling of the arc process for fullerene and carbon nanotube production using O-D, 1-D and 2-D fluid flow models. The third part addresses simulations of the pulsed laser ablation process using time-dependent techniques in 2-D, and a steady state 2-D simulation of a continuous laser ablation process. The fourth part addresses steady state modeling in O-D and 2-D of the HiPco process. In each of the simulations, there is a variety of simplifications that are made that enable one to concentrate on one aspect or another of the process. There are simplifications that can be made to the chemical reaction models , e.g. reduction in number of species by lumping some of them together in a representative species. Other simulations are carried out by eliminating the chemistry altogether in order to concentrate on the fluid dynamics. When solving problems with a large number of species in more than one spatial dimension, it is almost imperative that the problem be decoupled by solving for the fluid dynamics to find the fluid motion and temperature history of "particles" of fluid moving through a reactor. Then one can solve the chemical rate equations with complex chemistry following the temperature and pressure history. One difficulty is that often mixing with an ambient gas is involved. Therefore, one needs to take dilution and mixing into account. This changes the ratio of carbon species to background gas. Commercially available codes may have no provision for including dilution as part of the input. One must the write special solvers for including dilution in decoupled problems. The article addresses both ful1erene production and single-walled carbon nanotube (SWNT) production. There are at least two schemes or concepts of SWNT growth. This article will only address growth in the gas phase by carbon and catalyst cluster growth and SW T formation by the addition of carbon. There are other models that conceive of SWNT growth as a phase separation process from clusters me up carbon and metal catalyst, with the carbon precipitating from the cluster as it cools. We will not deal with that concept in this article. Further research is needed to determine the rates at which these composite clusters form, evaporate, and segregate.

Scott, Carl D.↗
DOE OSTI2020

Materials Data on Te2As2SI6(OF6)2 by Materials Project

AsTeF4(AsF3)2AsTeIF5As3Te3SO6I13F25AsSI2F3OIS1SI2Te2OI4F4TeIF crystallizes in the triclinic P1 space group. The structure is one-dimensional and consists of one ctk7c3725 molecule; two trifluoroarsine molecules; one AsSI2F3 cluster; one AsTeF4 cluster; one AsTeIF5 cluster; one OIS1 cluster; one Te2OI4F4 cluster; one TeIF cluster; and one As3Te3SO6I13F25 ribbon oriented in the (1, 0, 0) direction. In the AsSI2F3 cluster, As5+ is bonded in a distorted T-shaped geometry to three F1- atoms. There is one shorter (1.77 Å) and two longer (1.78 Å) As–F bond length. S2- is bonded in a 3-coordinate geometry to two I and one F1- atom. There are one shorter (2.41 Å) and one longer (2.42 Å) S–I bond lengths. The S–F bond length is 3.11 Å. There are two inequivalent I sites. In the first I site, I is bonded in a single-bond geometry to one S2- atom. In the second I site, I is bonded in a single-bond geometry to one S2- atom. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As5+ and one S2- atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the AsTeF4 cluster, As5+ is bonded in a distorted T-shaped geometry to three F1- atoms. There is two shorter (1.76 Å) and one longer (1.82 Å) As–F bond length. Te4+ is bonded in a distorted linear geometry to two F1- atoms. There are one shorter (1.96 Å) and one longer (2.60 Å) Te–F bond lengths. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the third F1- site, F1- is bonded in a distorted bent 120 degrees geometry to one As5+ and one Te4+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the AsTeIF5 cluster, As5+ is bonded in a distorted T-shaped geometry to three F1- atoms. There are a spread of As–F bond distances ranging from 1.75–1.91 Å. Te4+ is bonded in a 2-coordinate geometry to one I and three F1- atoms. The Te–I bond length is 2.86 Å. There are a spread of Te–F bond distances ranging from 1.91–2.39 Å. I is bonded in a 1-coordinate geometry to one Te4+ atom. There are five inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the fourth F1- site, F1- is bonded in a 2-coordinate geometry to one As5+ and one Te4+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the OIS1 cluster, S2- is bonded in a distorted single-bond geometry to one O2- and one I atom. The S–O bond length is 1.47 Å. The S–I bond length is 2.55 Å. O2- is bonded in a single-bond geometry to one S2- atom. I is bonded in a distorted single-bond geometry to one S2- atom. In the Te2OI4F4 cluster, there are two inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a distorted linear geometry to two I and two F1- atoms. There are one shorter (2.70 Å) and one longer (2.71 Å) Te–I bond lengths. There are one shorter (1.97 Å) and one longer (2.19 Å) Te–F bond lengths. In the second Te4+ site, Te4+ is bonded in a 3-coordinate geometry to one O2- and two F1- atoms. The Te–O bond length is 2.29 Å. There is one shorter (1.92 Å) and one longer (1.95 Å) Te–F bond length. O2- is bonded in a 3-coordinate geometry to one Te4+ and two I atoms. There are one shorter (2.05 Å) and one longer (2.29 Å) O–I bond lengths. There are four inequivalent I sites. In the first I site, I is bonded in a 1-coordinate geometry to one O2- atom. In the second I site, I is bonded in a 1-coordinate geometry to one Te4+ atom. In the third I site, I is bonded in a linear geometry to one O2- and one F1- atom. The I–F bond length is 2.43 Å. In the fourth I site, I is bonded in a distorted single-bond geometry to one Te4+ atom. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the third F1- site, F1- is bonded in a distorted water-like geometry to one Te4+ and one I atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the TeIF cluster, Te4+ is bonded in a distorted single-bond geometry to one I and one F1- atom. The Te–I bond length is 2.69 Å. The Te–F bond length is 1.96 Å. I is bonded in a single-bond geometry to one Te4+ atom. F1- is bonded in a single-bond geometry to one Te4+ atom. In the As3Te3SO6I13F25 ribbon, there are three inequivalent As5+ sites. In the first As5+ site, As5+ is bonded in a distorted trigonal non-coplanar geometry to two O2- and one F1- atom. There is one shorter (1.79 Å) and one longer (1.83 Å) As–O bond length. The As–F bond length is 1.78 Å. In the second As5+ site, As5+ is bonded in a distorted rectangular see-saw-like geometry to one O2- and three F1- atoms. The As–O bond length is 2.19 Å. There are a spread of As–F bond distances ranging from 1.75–1.90 Å. In the third As5+ site, As5+ is bonded in a distorted T-shaped geometry to three F1- atoms. There is two shorter (1.80 Å) and one longer (1.82 Å) As–F bond length. There are three inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 3-coordinate geometry to four F1- atoms. There are a spread of Te–F bond distances ranging from 1.92–2.79 Å. In the second Te4+ site, Te4+ is bonded in a 3-coordinate geometry to one O2- and three F1- atoms. The Te–O bond length is 2.06 Å. There are a spread of Te–F bond distances ranging from 1.99–2.87 Å. In the third Te4+ site, Te4+ is bonded in a 3-coordinate geometry to four F1- atoms. There are a spread of Te–F bond distances ranging from 1.91–2.83 Å. S2- is bonded in a trigonal non-coplanar geometry to two I and one F1- atom. There are one shorter (2.40 Å) and one longer (2.44 Å) S–I bond lengths. The S–F bond length is 3.34 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one As5+ and one I atom. The O–I bond length is 1.86 Å. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two I atoms. There are one shorter (2.00 Å) and one longer (2.13 Å) O–I bond lengths. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Te4+ and one I atom. The O–I bond length is 1.95 Å. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one I atom. The O–I bond length is 1.83 Å. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one As5+ and one I atom. The O–I bond length is 1.97 Å. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one As5+ and one I atom. The O–I bond length is 2.05 Å. There are thirteen inequivalent I sites. In the first I site, I is bonded in a linear geometry to two F1- atoms. There are one shorter (2.04 Å) and one longer (2.17 Å) I–F bond lengths. In the second I site, I is bonded in a single-bond geometry to one I and one F1- atom. The I–I bond length is 2.98 Å. The I–F bond length is 2.03 Å. In the third I site, I is bonded in a linear geometry to two F1- atoms. There are one shorter (2.03 Å) and one longer (2.38 Å) I–F bond lengths. In the fourth I site, I is bonded in a linear geometry to two F1- atoms. There are one shorter (1.96 Å) and one longer (2.45 Å) I–F bond lengths. In the fifth I site, I is bonded in a single-bond geometry to one O2- atom. In the sixth I site, I is bonded in a 1-coordinate geometry to one S2-, one I, and one F1- atom. The I–F bond length is 3.35 Å. In the seventh I site, I is bonded in a distorted single-bond geometry to one S2- and one F1- atom. The I–F bond length is 2.49 Å. In the eighth I site, I is bonded in a distorted single-bond geometry to one O2- and one F1- atom. The I–F bond length is 3.19 Å. In the ninth I site, I is bonded in a 4-coordinate geometry to one O2- and three F1- atoms. There are a spread of I–F bond distances ranging from 2.00–2.97 Å. In the tenth I site, I is bonded in a T-shaped geometry to one O2- and two F1- atoms. There are one shorter (1.98 Å) and one longer (2.09 Å) I–F bond lengths. In the eleventh I site, I is bonded in a T-shaped geometry to one O2- and two F1- atoms. There are one shorter (1.96 Å) and one longer (2.53 Å) I–F bond lengths. In the twelfth I site, I is bonded in a linear geometry to one O2- and one F1- atom. The I–F bond length is 2.48 Å. In the thirteenth I site, I is bonded in a distorted linear geometry to one O2- and one F1- atom. The I–F bond length is 2.73 Å. There are twenty-five inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one I atom. In the second F1- site, F1- is bonded in a single-bond geometry to one I atom. In the third F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one I atom. In the sixth F1- site, F1- is bonded in a distorted single-bond geometry to one I atom. In the seventh F1- site, F1- is bonded in a distorted single-bond geometry to one As5+ and one Te4+ atom. In the eighth F1- site, F1- is bonded in a distorted single-bond geometry to one Te4+ atom. In the ninth F1- site, F1- is bonded in a distorted bent 120 degrees geometry to two I atoms. In the tenth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the eleventh F1- site, F1- is bonded in a distorted bent 120 degrees geometry to one As5+ and one I atom. In the twelfth F1- site, F1- is bonded in a single-bond geometry to one I atom. In the thirteenth F1- site, F1- is bonded in a distorted water-like geometry to three I atoms. In the fourteenth F1- site, F1- is bonded in a single-bond geometry to one Te4+ and one I atom. In the fifteenth F1- site, F1- is bonded in a single-bond geometry to one As5+ and one I atom. In the sixteenth F1- site, F1- is bonded in a distorted single-bond geometry to one Te4+ and one S2- atom. In the seventeenth F1- site, F1- is bonded in a single-bond geometry to one I atom. In the eighteenth F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the nineteenth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the twentieth F1- site, F1- is bonded in a distorted single-bond geometry to one As5+ and one Te4+ atom. In the twenty-first F1- site, F1- is bonded in a 3-coordinate geometry to one Te4+ and two I atoms. In the twenty-second F1- site, F1- is bonded in a distorted single-bond geometry to one As5+ and one I atom. In the twenty-third F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the twenty-fourth F1- site, F1- is bonded in a single-bond geometry to one Te4+ atom. In the twenty-fifth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two I atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Enhancing NO Reduction by CO Over NiO/CeO 2 Catalyst by Optimizing the Metal Oxide–Support Interaction

Noble metal catalysts are widely used in three-way catalysts (TWCs) due to their high efficiency, but their scarcity and high cost drive the need for effective, low-cost alternatives. Here, in this work, a series of NiO/CeO 2 catalysts were engineered by modulating the OH content and crystallite size of the CeO 2 support. This approach yielded Ni species ranging from isolated single atoms to small clusters and larger aggregates, with varied NiO/CeO 2 interaction strengths. Evaluation of their performance in NO reduction by CO, CO oxidation, and the water–gas shift reaction revealed that the NiO/CeO 2 -300 catalyst, featuring small CeO 2 crystallites and highly dispersed NiO clusters, delivered superior activity for NO reduction and CO oxidation. It was demonstrated that small NiO clusters, due to their efficient CO adsorption and activation, were more active than Ni single atoms. Furthermore, the presence of water was found to influence the catalyst stability, with NiO clusters less stable than single atoms likely due to the hydroxylation effect leading to the formation of Ni(OH) 2 . Oxygen storage capacity measurements revealed that performance was governed by a combination of CeO 2 crystallite size and the abundance of NiO/CeO 2 interfaces. These findings demonstrated that the catalytic performance of Ni/CeO 2 systems could be maximized by optimizing the Ni nanostructure and its interaction with CeO 2 support, positioning them as a promising, multifunctional nonprecious alternative for three-way catalysis application.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Resolving the Atomic Structure of Sequential Infiltration Synthesis Derived Inorganic Clusters

Sequential infiltration synthesis (SIS) is a route to the precision deposition of inorganic solids in analogy to atomic layer deposition but occurs within (vs upon) a soft material template. SIS has enabled exquisite nanoscale morphological complexity in various oxides through selective nucleation in block copolymers templates. However, the earliest stages of SIS growth remain unresolved, including the atomic structure of nuclei and the evolution of local coordination environments, before and after polymer template removal. We employed In K-edge extended X-ray absorption fine structure and atomic pair distribution function analysis of high-energy X-ray scattering to unravel (1) the structural evolution of InO x H y clusters inside a poly(methyl methacrylate) (PMMA) host matrix and (2) the formation of porous In 2 O 3 solids (obtained after annealing) as a function of SIS cycle number. Early SIS cycles result in InO x H y cluster growth with high aspect ratio, followed by the formation of a three-dimensional network with additional SIS cycles. That the atomic structures of the InO x H y clusters can be modeled as multinuclear clusters with bonding patterns related to those in In 2 O 3 and In(OH) 3 crystal structures suggests that SIS may be an efficient route to 3D arrays of discrete-atom-number clusters. As a result, annealing the mixed inorganic/polymer films in air removes the PMMA template and consolidates the as-grown clusters into cubic In 2 O 3 nanocrystals with structural details that also depend on SIS cycle number.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Nova dust nucleation - Kinetics and photodissociation

Dust is observed to form in nova ejecta. The grain temperature is determined by the diluted nova radiation field rather than the gas kinetic temperature, making classical nucleation theory inapplicable. We used kinetic equations to calculate the growth of carbon nuclei in these ejecta. For expected values of the parameters too many clusters grew, despite the small sticking probability of atoms to small clusters, and the clusters only reached radii of about 100 A when the carbon vapor was depleted. We then included the effects of cluster photodissociation by ultraviolet radiation from the nova. This suppresses nucleation, but too well, and no grains form at all. Finally we suggest that a few growing carbon nuclei may be protected from photodissociation by a sacrificial surface layer of hydrogen.

Johnson, D. J.↗
DOE OSTI2023

High-Spin and Reactive Fe 13 Cluster with Exposed Metal Sites

We report atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp* 4 W 4 Fe 13 S 12 , displaying a Fe 13 core with M-M bonds that has precedent only in main group and late metal chemistry. M 13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp* 4 W 4 Fe 13 S 12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.

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

Hydrogen Localization and Cluster Formation in α-Zr from First-Principles Investigations

We report alpha-zirconium (α-Zr) is a hydrogen atom host material used in nuclear energy and semiconducting applications due to Zr's excellent properties such as corrosion resistance, low thermal neutrons cross-section, and thermodynamically favorable interstitial sequestering of H atoms. Herein we use density functional theory simulations to systematically analyze the initial stages of H insertion in the Zr matrix, and determine optimal hydrogen localization, distribution, and clustering tendencies from a thermodynamics and kinetics perspective. Our results suggest that H occupation of tetrahedral sites is strongly favored, consistent with previous experimental and theoretical studies. Further, a cooperative effect in H localization is shown where H atoms favor clustering. The H pair is found to be the most stable by occupying tetrahedral sites with pairs at second nearest-neighbor positions (TTn2). Among the four H atom clusters, the most favorable configuration has two TTn2 pairs forming "box " or "zig-zag" shaped-cluster with the pairs separated by 3.03 or 3.25 Å, respectively. Nudged elastic band simulations suggest that the formation of TTn2 is facile and is limited by the small diffusion barrier of the monomer of less than 0.1 eV. Further, the formation routes for the 4H atom clusters are also presented. The current study can serve as a foundation to systematically model H atom clustering in metals and alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Solute clustering in polycrystals: Unveiling the interplay of grain boundary junction and long-range solute attraction effects

Spectral analysis of local atomic environments has become a powerful tool for studying solute atom segregation and interactions at grain boundaries in nanocrystalline alloys. When applied to individual grain boundaries, the spectral analysis has shown that solute-solute interaction can be either attractive or repulsive, with long-range relative attraction enhancing the likelihood for solute atoms to begin clustering. In this article, we combine this analysis with a new grain-boundary structure descriptor based on grain-boundary atom coordination, to investigate the impact of grain-boundary junctions on solute atom segregation in polycrystals. Specifically, we systematically characterize the tendency of solute clusters to begin forming at various types of ordinary grain boundaries, triple junctions, and high-order junctions in Ag polycrystals containing either Ni or Cu solute atoms. Our findings demonstrate that the formation of solute clusters at grain boundaries is primarily driven by long-range relative solute attraction, rather than short-range solute-solute interactions. Furthermore, this effect is most pronounced near grain-boundary junctions. Our study highlights the multiscale nature of solute segregation at crystalline interfaces and provides new insights into the complex phenomena governing heterogeneous solute segregation in grain-boundary networks.

Grain-boundary junction↗
DOE OSTI2022

Helium interaction with solutes and impurities in neutron-irradiated nanostructured ferritic alloys: A first principles study

Density functional theory calculations are performed to explore the binding between He and alloying solutes, impurities, and transmutation products expected in neutron irradiated nanostructured ferritic alloys (NFAs), here 14YWT is taken as an example. Elements that exhibit significant binding (attraction) with an interstitial He are Y (binding energy = 0.46 eV), Mg (0.32), O (0.33), Ti (0.16), and C (0.15). Those that provide significant binding to a substitutional He are O (1.44), Y (1.24), N (0.73), H (0.56), Mg (0.52), Ti (0.34), Si (0.34), C (0.33), Al (0.32), Ni (0.26), Ta (0.23), and Mn (0.16). The presence of these elements in Fe matrix could reduce the transport of He towards oxide particles, dislocations, and internal boundaries, and could promote He bubble nucleation in the matrix. For convenience, we compile existing binding energy data of He with He n and He n V (He-vacancy) clusters. Dissociation pathway analysis reveals that, in general, the most likely dissociation of a He n V cluster is by a sequential emission of individual He atoms. Furthermore, larger bubbles are more prone to dissociation than smaller ones. In addition, we estimate the binding energy (segregation energy) of He in bulk Y 2 Ti 2 O 7 (YTO) single crystal, YTO/Fe interface, and YTO particle embedded in Fe, with respect to interstitial He in Fe, from existing formation energies of He in these structures. We also compile available data of He binding with Fe self-interstitial atom (SIA), SIA clusters, and edge and screw dislocations. Note that given the absence of DFT data, the binding with SIA clusters and dislocations are gathered from simulations with empirical potentials. Finally, the data presented in this paper is important to inform multiscale simulations of He bubble accumulation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Te3As2S(OF6)2 by Materials Project

(Te)3AsTeF6AsTe2F6(AsF6)2(SO2)2 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four sulfur dioxide molecules, six tellurium molecules, four AsF6 clusters, two AsTe2F6 clusters, and two AsTeF6 clusters. In each AsF6 cluster, As5+ is bonded in an octahedral geometry to six F1- atoms. There are a spread of As–F bond distances ranging from 1.77–1.79 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the sixth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In each AsTe2F6 cluster, As5+ is bonded in an octahedral geometry to six F1- atoms. There are a spread of As–F bond distances ranging from 1.75–1.80 Å. There are two inequivalent Te+2.67+ sites. In the first Te+2.67+ site, Te+2.67+ is bonded in a single-bond geometry to one F1- atom. The Te–F bond length is 2.84 Å. In the second Te+2.67+ site, Te+2.67+ is bonded in a single-bond geometry to one F1- atom. The Te–F bond length is 2.82 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As5+ and one Te+2.67+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As5+ and one Te+2.67+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the sixth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In each AsTeF6 cluster, As5+ is bonded in an octahedral geometry to six F1- atoms. There are a spread of As–F bond distances ranging from 1.76–1.80 Å. Te+2.67+ is bonded in a distorted single-bond geometry to one F1- atom. The Te–F bond length is 2.86 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one As5+ and one Te+2.67+ atom. In the sixth F1- site, F1- is bonded in a single-bond geometry to one As5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Extended x-ray emission times of clusters in intense x-ray pulses

Novel experimental spectroscopic and imaging techniques have been developed to exploit x-ray free-electron laser (XFEL) for studying structure and dynamic of non-periodic entities at atomic spatial resolution and femtosecond timescales.Recently, intensity correlation of x-ray fluorescence, based on the principle introduced by Hanbury Brown and Twiss [R. Hanbury Brown and R. Q. Twiss, Nature (London) 177, 27 (1956)], has been proposed for high-resolution imaging of a three-dimensional arrangement of atoms. To explore the applicability of this fluorescence approach, we theoretically investigate fluorescence dynamics of nonperiodic systems subject to x-ray free electron laser (XFEL) pulses over a range of fluences from the linear to nonlinear x-ray absorption regimes as a function of system size, from a single atom to a cluster of 149 171 atoms. Fluorescence dynamics in the nonlinear x-ray regime differs from that in the weak x-ray field in that intense x-ray pulses interrupt the fluorescence dynamics by multiphoton absorption creating a dense electron environment within the sample on a femtosecond timescale. In large systems, the presence of both recombination and photoionization pathways gives rise to an enhanced Kα and Kα h emission yield and an extended emission time beyond the lifetime of the core-excited states. Our analysis suggests that, in an intense x-ray pulse, the Kα h emission line can be a good candidate for fluorescence imaging as it has a higher yield and an emission time that is short relative to the x-ray-induced lattice distortion time.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

What atoms do when they get together

How atoms organize during the earliest stages of nucleation has been a subject of speculation for over a century. Using atomically resolved electron microscopy, the formation and ordering of metal clusters from individual atoms has now been observed in carbon nanotubes that serve as ‘test tubes’.

De Yoreo, James J.↗
DOE OSTI2021

Thermal gradient effect on helium and self-interstitial transport in tungsten

First-wall materials in a fusion reactor are expected to withstand harsh conditions, with high heat and particle fluxes that modify the materials microstructure. These fluxes will create strong gradients of temperature and concentration of diverse species. Besides the He ash and the hydrogenic species, neutron particles generated in the fusion reaction will collide with the material creating intrinsic defects, such as vacancies, self-interstitials atoms (SIAs), and clusters of such point defects. These defects and the He atoms will then migrate in the presence of the aforementioned gradients. In this study, we use nonequilibrium molecular dynamics to analyze the transport of He and SIAs in the presence of a thermal gradient in tungsten. We observe that, in all cases, the defects and impurity atoms tend to migrate toward the hot regions of the tungsten sample. The resulting species concentration profiles are exponential distributions, rising toward the hot regions of the sample, in agreement with irreversible thermodynamics analysis. For both He atoms and SIAs, we find that the resulting species flux is directed opposite to the heat flux, indicating that species transport is governed by a Soret effect (thermal-gradient-driven diffusion) characterized by a negative heat of transport that drives species diffusion uphill (from the cooler to the hot regions of the sample). Here, we demonstrate that the steady-state species profiles obtained accounting for the Soret effect vary significantly from those where temperature-gradient-driven transport is not considered and discuss the implications of such a Soret effect on the response to plasma exposure of plasma-facing tungsten.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Generalized representative structures for atomistic systems

A new method is presented to generate atomic structures that reproduce the essential characteristics of arbitrary material systems, phases, or ensembles. Previous methods allow one to reproduce the essential characteristics (e.g. the chemical disorder) of a large random alloy within a small crystal structure. The ability to generate small representations of random alloys, along with the restriction to crystal systems, results from using the fixed-lattice cluster correlations to describe structural characteristics. A more general description of the structural characteristics of atomic systems is obtained using complete sets of atomic environment descriptors. These are used within for generating representative atomic structures without restriction to fixed lattices. A general data-driven approach is provided here utilizing the atomic cluster expansion (ACE) basis. The N-body ACE descriptors are a complete set of atomic environment descriptors that span both chemical and spatial degrees of freedom and are used within for describing atomic structures. The generalized representative structure (GRS) method presented within generates small atomic structures that reproduce ACE descriptor distributions corresponding to arbitrary structural and chemical complexity. It is shown that systematically improvable representations of crystalline systems on fixed parent lattices, amorphous materials, liquids, and ensembles of atomic structures may be produced efficiently through optimization algorithms. With the GRS method, we highlight reduced representations of atomistic machine-learning training datasets that contain similar amounts of information and small 40–72 atom representations of liquid phases. The ability to use GRS methodology as a driver for informed novel structure generation is also demonstrated. The advantages over other data-driven methods and state-of-the-art methods restricted to high-symmetry systems are highlighted.

atomic cluster expansion↗
DOE OSTI2020

Materials Data on Ni(ClO2)2 by Materials Project

NiO4NiCl4NiO4ClO2ClO2 crystallizes in the triclinic P1 space group. The structure is zero-dimensional and consists of one 67952-07-2 molecule, one oxygen molecule, one NiCl4 cluster, one NiO4 cluster, and one NiO4Cl cluster. In the NiCl4 cluster, Ni is bonded in a tetrahedral geometry to four Cl atoms. There are three shorter (2.16 Å) and one longer (2.19 Å) Ni–Cl bond lengths. There are four inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to one Ni atom. In the second Cl site, Cl is bonded in a single-bond geometry to one Ni atom. In the third Cl site, Cl is bonded in a single-bond geometry to one Ni atom. In the fourth Cl site, Cl is bonded in a single-bond geometry to one Ni atom. In the NiO4 cluster, Ni is bonded in a trigonal planar geometry to three O atoms. There is two shorter (1.60 Å) and one longer (1.95 Å) Ni–O bond length. There are four inequivalent O sites. In the first O site, O is bonded in a distorted bent 120 degrees geometry to one Ni and one O atom. The O–O bond length is 1.25 Å. In the second O site, O is bonded in a single-bond geometry to one O atom. In the third O site, O is bonded in a single-bond geometry to one Ni atom. In the fourth O site, O is bonded in a single-bond geometry to one Ni atom. In the NiO4Cl cluster, Ni is bonded in a T-shaped geometry to three O atoms. There are a spread of Ni–O bond distances ranging from 1.76–2.04 Å. There are four inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one O atom. The O–O bond length is 1.24 Å. In the second O site, O is bonded in a bent 120 degrees geometry to one Ni and one O atom. In the third O site, O is bonded in a single-bond geometry to one Ni atom. In the fourth O site, O is bonded in a bent 120 degrees geometry to one Ni and one Cl atom. The O–Cl bond length is 1.62 Å. Cl is bonded in a single-bond geometry to one O atom.

36 MATERIALS SCIENCE↗