Negative Thermal Expansion Design Strategies in a Diverse Series of Metal–Organic Frameworks
Abstract not provided
Burtch, Nicholas C.↗
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Results for “total scattering”
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Combining Experimental and Theoretical Techniques to Gain an Atomic Level Understanding of the Defect Binding Mechanism in Hard Carbon Anodes for Sodium Ion Batteries
Sodium ion batteries (NIBs) are an attractive alternative to lithium–ion batteries in applications that require large–scale energy storage due to sodium's high natural abundance and low cost. Hard carbon (HC) is the most promising anode material for NIBs; however, there is a knowledge gap in the understanding of the sodium binding mechanism that prevents a rational design of HC. This study tunes sucrose–derived HC via synthesis temperature then evaluates the structural, physical, and electrochemical properties. Neutron total scattering is used to generate structural models by fitting pair distribution functions (PDF) with a combination of molecular dynamics and reverse Monte Carlo methods. From this model, the number and type of structural features are identified, quantified, and correlated to the galvanostatic charge/discharge. A method of PDF “fingerprinting” binding sites using Na probe atoms is developed and analyzing these PDFs reveals an atomistic view of ion binding sites responsible for “defect” storage mechanisms. Combining these techniques results in an atomic–level study that provides a big picture of the Na–binding mechanism in NIBs, which allows for more precise tuning of the structure–property relationships in the future. Finally, the methodologies developed will also enable new strategies for the analysis of amorphous functional materials.
25 ENERGY STORAGE↗
Improving the picture of atomic structure in nonoriented polymer domains using the pair distribution function: A study of polyamide 6
Abstract Investigations of the atomic structures within polyamides started over 80 years ago and continue today. These weakly ordered materials diffract X‐rays poorly and typically require postprocessing to obtain idealized samples for structural studies. An important goal remains to develop techniques to study the local structure in its natural state, with atomic resolution, and with sensitivity to subtle changes due to synthesis conditions or other technologically relevant processing procedures. Here, we compare the structures of as‐produced, nonoriented polyamide 6 ([C 6 H 11 NO] n ) from both hydrolytic and anionic processes. A total scattering pair distribution function approach is used to elucidate information about the atomic bonding, molecular conformation, chain packing, crystallite size, and ratio of ordered to disordered domain content. The results are compared with those from standard analytical methods.
Terban, Maxwell W.↗
Pressure‐induced polyamorphism in lanthanide‐solute metallic glasses
The electronic structure inheritance of lanthanide‐solvent atoms in lanthanide‐based metallic glasses has been proposed. Is a polyamorphism possible in lanthanide‐solute metallic glasses? So far, polyamorphic phase transitions in metallic glass containing lanthanide have been observed only in lanthanide‐solvent metallic glasses. Here, a pressure‐induced transition between two distinct amorphous states, accompanied by a 7% volume collapse at ambient pressure, was observed in La 43.4 Pr 18.6 Al 14 Cu 24 metallic glass, with low lanthanide content, by using in situ X‐ray total scattering method. The transformation also indicated by changes in short range and medium range order. Thus, it is proposed that the lanthanide‐solute metallic glasses also inherit 4 f electronic transition from pure lanthanide element in polyamorphic transition. This discovery offers a supplement to research on lanthanide‐based metallic glasses, which further provides a new perspective of the polyamorphic transformation in metallic glasses containing lanthanide element.
Li, Liangliang↗
The Central Role of Oxo Clusters in Zirconium‐Based Esterification Catalysis
Oxo clusters are a unique link between oxide nanocrystals and Metal‐Organic Frameworks (MOFs), representing the limit of downscaling each of the respective crystals. Herein, the superior catalytic activity of clusters, compared to zirconium MOF UiO‐66 and nanocrystals is shown. Focus is on esterification reactions given their general importance in consumer products and the challenge of converting large substrates. Oxo clusters have a higher surface‐to‐volume ratio than nanocrystals, rendering them more active. For large substrates, for example, oleic acid, MOF UiO‐66 has negligible catalytic activity while clusters provide almost quantitative conversion, a fact we ascribe to limited diffusion of large substrates through the MOF pores. Clusters do not suffer from limited mass transfer and we also obtain high conversion in solvent‐free reactions with sterically hindered alcohols (hexanol, 2‐ethyl hexanol, benzyl alcohol, and neopentyl alcohol). The cluster catalyst can be recovered and shows identical activity when reused. The structural integrity of the cluster is confirmed using X‐ray total scattering and pair distribution function analysis. Moreover, when homogeneous zirconium alkoxides are used as catalysts, the same oxo cluster is retrieved, showing that oxo clusters are the active catalytic species, even in previously assumed homogeneously catalyzed reactions.
Pulparayil Mathew, Jikson↗
Breaking with the Principles of Coreduction to Form Stoichiometric Intermetallic PdCu Nanoparticles
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Mathiesen, Jette K.↗
GeoSoilEnviroCARS (Sector 13) at the Advanced Photon Source: a comprehensive synchrotron radiation facility for Earth science research at ambient and extreme conditions
GeoSoilEnviroCARS (GSECARS) is a comprehensive analytical laboratory for Earth and environmental science research using X-ray beams from the Advanced Photon Source, Argonne National Laboratory. State-of-the-art instruments are available for (1) high-pressure/high- or low-temperature diffraction, total scattering, and spectroscopy (Brillouin, Raman, and VIS-IR) using the laser heated diamond anvil cell (DAC); (2) high-pressure/high-temperature diffraction, scattering, and imaging as well as acoustic emission (AE) and ultrasonics using the large-volume press (LVP); (3) powder, single crystal, and surface/interface diffraction; (4) X-ray absorption fine structure spectroscopy; (5) X-ray fluorescence microprobe analysis; and (6) microtomography. As shown here, experiments are facilitated by senior level staff who collaborate on all aspects of the analytical work including experiment design, sample preparation, data collection, data interpretation, and publication preparation. Both technical and scientific synergies occur as a result of the intimate association of the various techniques and scientists experienced in the applications of synchrotron radiation to Earth, environmental, and planetary science problems. The facility includes state-of-the-art instrumentation designed and built in-house, including custom X-ray optics, online and offline laser-based systems, specialized sample environments and positioning systems, as well as pixel-array and multi-crystal energy dispersive X-ray detectors, which are available to be shared among the experimental stations.
36 MATERIALS SCIENCE↗
Similar local order in disordered fluorite and aperiodic pyrochlore structures
A major challenge to understanding the response of materials to extreme environments ( e.g. , nuclear fuels/waste forms and fusion materials) is to unravel the processes by which a material can incorporate atomic-scale disorder, and at the same time, remain crystalline. While it has long been known that all condensed matter, even liquids and glasses, possess short-range order, the relation between fully-ordered, disordered, and aperiodic structures over multiple length scales is not well understood. For example, when defects are introduced ( via pressure or irradiation) into materials adopting the pyrochlore structure, these complex oxides either disorder over specific crystallographic sites, remaining crystalline, or become aperiodic. Here we present neutron total scattering results characterizing the irradiation response of two pyrochlores, one that is known to disorder (Er 2 Sn 2 O 7 ) and the other to amorphize (Dy 2 Sn 2 O 7 ) under ion irradiation. The results demonstrate that in both cases, the local pyrochlore structure is transformed into similar short range configurations that are best fit by the orthorhombic weberite structure, even though the two compositions have distinctly different structures, aperiodic vs. disordered-crystalline, at longer length scales. Thus, a material's resistance to amorphization may not depend primarily on local defect formation energies, but rather on the structure's compatibility with meso-scale modulations of the local order in a way that maintains long-range periodicity.
36 MATERIALS SCIENCE↗
Disordered interfaces enable high temperature thermal stability and strength in a nanocrystalline aluminum alloy
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99 GENERAL AND MISCELLANEOUS↗
Parameterized representation of macroscopic cross section for PWR reactor
Here we describe, by means of Chebyshev polynomials, a parameterized representation of the homogenized macroscopic cross section for PWR fuel element as a function of soluble boron concentration, moderator temperature, fuel temperature, moderator density and U-235(92) enrichment. The cross-section data analyzed are fission, scattering, total, transport, absorption and capture. The parameterization enables a quick and easy determination of problem-dependent cross-sections to be used in few group calculations. The methodology presented in this paper will allow generation of group cross-section data from stored polynomials to perform PWR core calculations without the need to generate them based on computer code calculations using standard steps. The results obtained by the proposed methodology when compared with results from the SCALE code calculations show very good agreement.
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
Intrinsic differences in atomic ordering of calcium (alumino)silicate hydrates in conventional and alkali-activated cements
The atomic structures of calcium silicate hydrate (C–S–H) and calcium (–sodium) aluminosilicate hydrate (C–(N)–A–S–H) gels, and their presence in conventional and blended cement systems, have been the topic of significant debate over recent decades. Previous investigations have revealed that synthetic C–S–H gel is nanocrystalline and due to the chemical similarities between ordinary Portland cement (OPC)-based systems and low-CO{sub 2} alkali-activated slags, researchers have inferred that the atomic ordering in alkali-activated slag is the same as in OPC–slag cements. Here, X-ray total scattering is used to determine the local bonding environment and nanostructure of C(–A)–S–H gels present in hydrated tricalcium silicate (C{sub 3}S), blended C{sub 3}S–slag and alkali-activated slag, revealing the large intrinsic differences in the extent of nanoscale ordering between C–S–H derived from C{sub 3}S and alkali-activated slag systems, which may have a significant influence on thermodynamic stability, and material properties at higher length scales, including long term durability of alkali-activated cements.
36 MATERIALS SCIENCE↗
Predicting CaO-(MgO)-Al2O3-SiO2 glass reactivity in alkaline environments from force field molecular dynamics simulations
In this investigation, force field-based molecular dynamics (MD) simulations have been employed to generate detailed structural representations for a range of amorphous quaternary CaO-MgO-Al{sub 2}O{sub 3}-SiO{sub 2} (CMAS) and ternary CaO-Al{sub 2}O{sub 3}-SiO{sub 2} (CAS) glasses. Comparison of the simulation results with select experimental X-ray and neutron total scattering and literature data reveals that the MD-generated structures have captured the key structural features of these CMAS and CAS glasses. Based on the MD-generated structural representations, we have developed two structural descriptors, specifically (i) average metal oxide dissociation energy (AMODE) and (ii) average self-diffusion coefficient (ASDC) of all the atoms at melting. Both structural descriptors are seen to more accurately predict the relative glass reactivity than the commonly used degree of depolymerization parameter, especially for the eight synthetic CAS glasses that span a wide compositional range. Hence these descriptors hold great promise for predicting CMAS and CAS glass reactivity in alkaline environments from compositional information.
36 MATERIALS SCIENCE↗
New insights in low-energy electron-fullerene interactions
The robust Regge-pole methodology has been used to probe for long-lived metastable anionic formation in C n (n = 20, 24, 26, 28, 44, 70, 92 and 112) through the calculated electron elastic scattering total cross sections (TCSs). All the TCSs are found to be characterized by Ramsauer-Townsend minima, shape resonances and dramatically sharp resonances manifesting metastable anionic formation during the collisions. The energy positions of the anionic ground states resonances are found to match the measured electron affinities (EAs). Here, we also investigated the size-effect through the correlation and polarization induced metastable resonances as the fullerene size varied from C 20 through C 112 . The C 20 TCSs exhibit atomic behavior while the C 112 TCSs demonstrate strong departure from atomic behavior attributed to the size effect. Surprisingly C 24 is found to have the largest EA among the investigated fullerenes making it suitable for use in organic solar cells and nanocatalysis.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Local structural mechanism for enhanced energy storage properties in heterovalent doped NaNbO 3 ceramics
In recent years, there is a growing interest for new lead-free oxides with reversible antiferroelectric (AFE)-ferroelectric (FE) phase transition for high-power energy-storage applications. NaNbO 3 -based ceramics are particularly attractive due to their easy synthesis and cost-effectiveness. In order to stabilize reversible AFE-FE phase transition, NaNbO 3 is doped with a combination of heterovalent substitutions, although the underlying structural mechanism for the same is poorly understood. Here, we investigated local and average structures of Ca/Zr doped NaNbO 3 using neutron total scattering. Here, we show that Ca/Zr doping increases the average AFE phase (Pbma) fraction, however, the material remains as a composite of both FE (P2 1 ma) and AFE regions. Analysis of local structure suggests that increase in the long-range AFE phase results from more extensive twinning of local FE regions, due to introduced charge disorder. We propose that enhanced energy-storage properties of Ca/Zr-doped NaNbO 3 arises from localized twin boundary motion between the defect-induced pinning centers.
25 ENERGY STORAGE↗
Pair distribution function analysis of neutron-irradiated silicon carbide
We have employed x-ray total scattering to investigate the structure of polycrystalline 3C-silicon carbide following neutron irradiation. Here, the structure as a function of irradiation temperature and dose was quantified by analyzing pair distribution functions. Although the SiC matrix retains its crystal structure after irradiation, a significant increase in the diffuse scattering component is observable indicating that neutron irradiation leads to changes in both the short- and medium-range order. These changes include both an irradiation dose- and temperature-dependent increase in the vacancy concentration leading to an increase in the Si and C atomic displacement parameters. A dose-dependent decrease in the size of defect free material is also quantified from the structural refinements due to an increase in the number of defects and defect clusters. Evidence of additional correlations in the short-range order (up to ~4 Å) from differential pair distribution function analysis indicate that combinations of atomistic defects including anti-site defects, vacancies and defect clusters are present after these irradiation conditions. Such structural information will be valuable for direct comparison of experimental and simulated atomic structures of irradiated silicon carbide.
36 MATERIALS SCIENCE↗
A small-box approach to the local crystal structure of Y 3 NbO 7
The local crystal structure of Y 3 NbO 7 was probed using neutron total scattering. Five different structural models were fit to the experimental pair distribution function of this material up to 15 Å. Fits of defect fluorite (Fm$\overline{3}$m), pyrochlore (Fd$\overline{3}$m), and orthorhombic C weberite models (C222 1 ) were attempted based on prior structural investigations of Y 3 NbO 7 and related fluorite-based materials. Orthorhombic P weberite (P222 1 ) and monoclinic weberite models (P112 1 ) were derived via symmetry reduction of the orthorhombic C weberite structure. All models except monoclinic weberite failed to reproduce the experimental pair distribution function. Misfits were clearly visible for peaks arising from atom pairs within the first coordination shell (defect fluorite and pyrochlore) and beyond (orthorhombic C and P weberite). By contrast, monoclinic weberite (γ ≈ 91.8°) provided an excellent fit, with no major misfits observed. This unit cell features distorted YO 8 dodecahedra, YO 7 monocapped octahedra, and NbO 6 octahedra as building blocks. Comparison between the topologies of the cationic and anionic substructures in monoclinic weberite and its parent orthorhombic C structure revealed displacements of the metal atoms along the [100] direction and a less compact spatial distribution of oxygen atoms along the a axis. In conclusion, the monoclinic weberite model presented herein may serve as a starting point to revisit structural modeling of fluorite-based materials with challenging local structures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗