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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Clathrate XI K 58 Zn 122 Sb 207 : A New Branch on the Clathrate Family Tree

Abstract The compositional screening of K‐Zn‐Sb ternary system aided by machine learning, rapid exploratory synthesis using KH salt‐like precursor and in situ powder X‐ray diffraction yielded a novel clathrate type XI K 58 Zn 122 Sb 207 . This clathrate consists of a 3D Zn‐Sb framework hosting K + ions inside polyhedral cages, some of which are reminiscent of known clathrate types while others are unique to this structure type. The complex non‐centrosymmetric structure in the tetragonal space group was solved by means of single crystal X‐ray diffraction as a 6‐component twin due to pseudocubic symmetry and further confirmed by high‐resolution synchrotron powder X‐ray diffraction and state‐of‐the‐art scanning transmission electron microscopy. The electron‐precise composition of this clathrate yields narrow‐gap p ‐type semiconductor with extraordinarily low thermal conductivity due to displacement or “rattling” of K cations inside oversized cages and as well as to twinning, stacking faults and antiphase boundary defects.

Cox, Tori↗
DOE OSTI2021

Quantitative Microstructural Characterization of Plutonium Oxalate Auto-Degradation and Evidence for PuO2 Nanocrystal Formation

It has been known since the 1950s that plutonium oxalate powders change color and lose mass over time when stored at room temperature in air. Despite several studies monitoring these changes, there are still discrepancies in the literature regarding the speciation of intermediate and final products that result from this decomposition. Presented here for the first time is a comprehensive series of time-resolved powder X-ray diffraction experiments coupled with solid-state optical spectroscopy and electron microscopy of aged plutonium (III) and (IV) oxalate powders. These data provide fresh insight into the chemical and structural changes that occur in these solids over time at room temperature and represent new evidence suggesting both plutonium (III) and plutonium (IV) oxalates decompose to form nanocrystalline plutonium oxide in the solid state.

Corbey, Jordan F.↗
NASA NTRS2020

X-Ray Diffraction and Reflectance Spectroscopy of Murchison Powders (CM2) After Thermal Analysis Under Reducing Conditions to Final Temperatures Between 300 and 1300°c

The asteroids Ryugu and Bennu have spectral characteristics in common with CI/CM type carbonaceous chondrites and are target bodies for JAXA’s Hayabusa2 and NASA’s OSIRIS-Rex missions, respectively. Analog studies, based primarily on the Murchison CM2 chondrite, provide a pathway to separate spectral properties resulting space weathering from those inherent to parent-body, mineralogy, chemistry, and processes. Ryugu shares spectral properties with thermally metamorphosed and partly dehydrated CI/CM chondrites. We have undertaken a multidisciplinary study of the thermal decomposition of Murchison powder samples as an analog to metamorphic process that may have occurred on Ryugu. Bulk analyses include thermal And evolved gas analysis, X-ray diffraction (XRD), and VIS-NIR and Mössbauer spectroscopy; micro- to nanoscale analyses included scanning and transmission electron microscopy and electron probe micro analysisWe report here XRD and VIS-NIR analyses of pre- and post-heated Murchison powders, and in a companion paper report results from multiple electron beam techniques.

Morris, R. V.↗
DOE OSTI2024

Electronic angle focusing for neutron time-of-flight powder diffractometers

A neutron time-of-flight (TOF) powder diffractometer with a continuous wide-angle array of detectors can be electronically focused to make a single pseudo-constant wavelength diffraction pattern, thus facilitating angle-dependent intensity corrections. The resulting powder diffraction peak profiles are affected by the neutron source emission profile and resemble the function currently used for TOF diffraction.

electronic focusing↗
DOE OSTI2020

Cooling dynamics of two titanium alloys during laser powder bed fusion probed with in situ X-ray imaging and diffraction

Metal parts produced by laser powder bed fusion (LPBF) additive manufacturing exhibit characteristic microstructures comparable to those observed in laser welding. The primary cause of this characteristic microstructure is rapid, localized heating and cooling cycles, which result in extreme thermal gradients where material solidification is followed by fast cooling in the solid state. The final microstructure and mechanical performance are also influenced by pore formation caused by melt pool fluid dynamics. Here, we use high speed, in situ X-ray diffraction to probe the kinetics of cooling and solid-solid phase transitions after laser melting in two aerospace titanium alloys: Ti-6Al-4V, an α + β alloy; and Ti-5Al-5V-5Mo-3Cr, a near-β alloy. We complement these diffraction studies with in situ X-ray imaging to probe melt pool dynamics and pore formation. From these two complementary probes, we quantify pore formation during melting and the subsequent microstructural evolution as the material rapidly cools after solidification. These results are critical for understanding defect formation and residual stress development in different titanium alloys under LPBF conditions and can help inform process models to predict final part performance.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Toward Design Principles for Diffusionless Transformations: The Frustrated Formation of Co–Co Bonds in a Low-Temperature Polymorph of GdCoSi 2

Diffusionless (or displacive) phase transitions allow inorganic materials to show exquisite responsiveness to external stimuli, as is illustrated vividly by the superelasticity, shape memory, and magnetocaloric effects exhibited by martensitic materials. In this Article, we present a new diffusionless transition in the compound GdCoSi 2 , whose origin in frustrated bonding points toward generalizable design principles for these transformations. We first describe the synthesis of GdCoSi 2 and the determination of its structure using single crystal X-ray diffraction. While previous studies based on powder X-ray diffraction assigned this compound to the simple CeNi 1–x Si 2 structure type (space group Cmcm), our structure solution reveals a superstructure variant (space group Pbcm) in which the Co sublattice is distorted to create zigzag chains of Co atoms. DFT-calibrated Hückel calculations, coupled with a reversed approximation Molecular Orbital (raMO) analysis, trace this superstructure to the use of Co–Co isolobal bonds to complete filled 18 electron configurations on the Co atoms, in accordance with the 18–n rule. The formation of these Co–Co bonds is partially impeded, however, by a small degree of electron transfer from Si-based electronic states to those with Co–Co σ* character. The incomplete success of Co–Co bond creation suggests that these interactions are relatively weak, opening the possibility of them being overcome by thermal energy at elevated temperatures. In fact, high-temperature powder and single crystal X-ray diffraction data, as well as differential scanning calorimetry, indicate that a reversible Pbcm to Cmcm transition occurs at about 380 K. This transition is diffusionless, and the available data point toward it being first-order. We expect that similar cases of frustrated interactions could be staged in other rare earth–transition metal–main group phases, providing a potentially rich source of compounds exhibiting diffusionless transformations and the unique properties these transitions mediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Syntheses, structures and selective dye adsorption of five formic-based coordination polymers prepared by in-situ hydrolysis of N, N′-dimethylformamide

Five functional coordination polymers (formic-based CPs) namely: ([Cu{sub 2}(CHOO){sub 3}(bibp){sub 2}]·CHOO){sub n} (1), ([Co{sub 2}(CHOO){sub 3}(bibp){sub 2}]·NO{sub 3}·H{sub 2}O)n (2), ([Ni{sub 2}(CHOO){sub 3}(bibp){sub 2}]·NO{sub 3}·H{sub 2}O){sub n} (3) [Co(CHOO){sub 2}(bbibp)]{sub n} (4) and [Zn(CHOO){sub 2}(bbibp)]{sub n} (5) (bibp=4,4′-bis(imidazolyl)biphenyl, bbibp=4,4′-bis(benzoimidazo-1-yl)biphenyl) have been successfully hydrothermally synthesized using the in-situ hydrolysis of N, N′-dimethylformamide (DMF) as the source of formate. All of these five polymers were characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analysis. Complexes 1–3 have the similar three-dimensional 3D kag topological framework built from the bibp ligand as the support member between the neighboring formic planes. Both complexes 4 and 5 have the similar one-dimensional 1D linear chain which is further assembled into 3D supermolecular structure by C–H…O hydrogen bonds. The dyes adsorption experiments have also been investigated systematically. The results show that complexes 2 and 3 exhibit high selective adsorption ability towards anionic dyes in their aqueous solution. Moreover, complex 2 displays good reversibility in the process of the dyes adsorption-release. Meanwhile, the unusual blocking phenomenon was firstly observed when complex 2 was in MO/OIV aqueous solutions with different concentration.

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

Crystal Chemistry and Structural Variations for Zircon Samples from Various Localities

This study investigates the variations of structural parameters and chemistry of a partially metamict and seven detrital zircon samples from different localities using single-crystal X-ray diffraction, synchrotron high-resolution powder X-ray diffraction, and electron-probe micro-analysis techniques. The unit-cell parameters for the eight zircon samples vary linearly with increasing unit-cell volume, V. A zircon sample from the Canadian Arctic Islands has the smallest unit-cell parameters, bond distances, ideal stoichiometric composition, unaffected by α-radiation damage, and is chemically pure. A zircon sample from Jemaa, Nigeria has the largest unit-cell parameters because of the effect of α-radiation doses received over a long time (2384 Ma). All the samples show good correlations between Zr and Si apfu (atom per formula unit) versus unit-cell volume, V. The α-radiation doses in the samples are lower than ~3.5 × 1015 α-decay events/mg. Substitutions of other cations at the Zr and Si sites control the variations of the structural parameters. Relatively large unit-cell parameters and bond distances occur because the Zr site accommodates other cations that have larger ionic radii than the Zr atom. Geological age increases the radiation doses in zircon and it is related to V.

58 GEOSCIENCES↗
NASA NTRS1969

Improved camera for better X-ray powder photographs

Camera obtains powder-type photographs of single crystals or polycrystalline powder specimens. X-ray diffraction photographs of a powder specimen are characterized by improved resolution and greater intensity. A reasonably good powder pattern of small samples can be produced for identification purposes.

Parrish, W.↗
DOE OSTI2015

Syntheses, structures, and properties of Co(II)/Zn(II) mixed-ligand coordination polymers based on 4-[(3,5-dinitrobenzoyl)amino]benzoic acid and 1,4-bis(1-imidazolyl) benzene

Two coordination polymers [Co(dnbab){sub 2}(bimb)](H{sub 2}O){sub 4} (1) and [Zn(dnbab){sub 2}(bimb)](H{sub 2}O){sub 5} (2) (Hdnbab=4-[(3,5-dinitrobenzoyl)amino]benzoic acid, bimb=1,4-bis(1-imidazolyl) benzene) have been solvothermally synthesized. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by powder X-ray diffraction (PXRD) and thermogravimetric (TG) analyses. Complexes 1 and 2 are isostructures and each displays an one-dimensional (1D) zigzag chain, which further forms a 3D supramolecular architecture with 1-D channels via inter-chain π–π interactions and hydrogen bonds. Moreover, the magnetic properties of 1 and fluorescent properties of 2 have been investigated. - Graphical abstract: Two coordination supramolecular frameworks [Co(dnbab){sub 2}(bimb)](H{sub 2}O){sub 4}(1) and [Zn(dnbab){sub 2}(bimb)](H{sub 2}O){sub 5}(2) (Hdnbab=4-[(3,5-dinitrobenzoyl)amino]benzoic acid, bimb=1,4-bis(1-imidazolyl) benzene) have been synthesized and characterized by X-ray single-crystal diffraction. Their thermal, magnetic and fluorescent properties have also been studied. - Highlights: • Two isomorphic Co(II)/Zn(II) complexes with the mixed-ligands have been synthesized. • Hydrogen bonds and π–π stacking interactions directed the final 3-D architecture assembly. • Both Co(II) and Zn(II) complexes show good thermal stability. • Co complex exhibits antiferromagnetic interaction. • The fluorescent property of Zn(II) complex has been investigated in the solid state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Zn(II) coordination polymers with flexible V-shaped dicarboxylate ligand: Syntheses, helical structures and properties

Hydrothermal reactions of 2,2′-[hexafluoroisopropylidenebis(p-phenyleneoxy)]diacetic acid (H{sub 2}L) and zinc ions in the presence of N-donor ancillary ligands afford four novel coordination polymers, namely, [Zn{sub 2}(μ{sub 2}-OH)(μ{sub 4}-O){sub 0.5}(L)]·0.5H{sub 2}O (1), [Zn(L)(2,2′-bipy)(H{sub 2}O)] (2), [Zn{sub 3}(L){sub 3}(phen){sub 2}]·H{sub 2}O (3) and [Zn{sub 2}(L){sub 2}(4,4′-bipy)] (4) (2,2′-bipy=2,2′-bipyridine; 4,4′-bipy=4,4′-bipyridine; phen=1,10-phenanthroline). Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectra, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Complex 1 shows a 3-D clover framework consisting of [Zn{sub 4}(µ{sub 4}-O)(µ{sub 2}-OH){sub 2}]{sup 4+} clusters, and exhibits a novel (3,8)-connected topological net with the Schläfli symbol of {3·4·5}{sub 2}{3"4·4"4·5"2·6"6·7"1"0·8"2}, and contains double-stranded and two kinds of meso-helices. 2 displays a helical chain structure, which is further extended via hydrogen bonds into a 3-D supramolecular structure with meso-helix chains. 3 displays a 2-D {4"4·6"2} parallelogram structure, which is further extended via hydrogen bonds into a 3-D supramolecular structure with single-stranded helical chains. 4 shows a 2-D {4"4·6"2} square structure with left- and right-handed helical chains. Moreover, the luminescent properties of 1–4 have been investigated. - Graphical abstract: Four new Zn(II) coordination polymers with helical structures based on flexible V-shaped dicarboxylate ligand have been synthesized and structurally characterized. Photoluminescent properties have been investigated. - Highlights: • Four novel Zn(II) coordination polymers with V-shaped ligand were characterized. • Complexes 1–4 show diverse intriguing helical characters. • Fluorescence properties of complexes 1–4 were investigated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Magneto acoustical emission in nanocrystalline Mn–Zn ferrites

Graphical abstract: Mn{sub 0.4}Zn{sub 0.6}Fe{sub 2}O{sub 4} powders were prepared by microwave hydrothermal method. The powders were characterized by X-ray diffraction, transmission electron microscope. The powders were sintered at different temperatures 400, 500, 600, 700, 800 and 900 °C/30 min using microwave sintering method. The grain size was estimated by scanning electron microscope. The room temperature dielectric and magnetic properties were studied in the frequency range (100 kHz–1.8 GHz). The magnetization properties were measured upto 1.5 T. The acoustic emission has been measured along the hysteresis loops from 80 K to Curie temperature. It is found that the magneto-acoustic emission (MAE) activity along hysteresis loop is proportional to the hysteresis losses during the same loop. This law has been verified on series of polycrystalline ferrites and found that the law is valid whatever the composition, the grain size and temperature. It is also found that the domain wall creation/or annihilation processes are the origin of the MAE. - Highlights: • The AE been measured along the hysteresis loops from 80 K to Curie temperature. • The MAE activity along hysteresis loop is proportional to P{sub h} during the same loop. • It is found that the domain wall creation/or annihilation processes are the origin of the MAE. - Abstract: Mn{sub 0.4}Zn{sub 0.6}Fe{sub 2}O{sub 4} powders were prepared by microwave hydrothermal method. The powders were characterized by X-ray diffraction, transmission electron microscope. The powders were sintered at different temperatures 400, 500, 600, 700, 800 and 900 °C/30 min using microwave sintering method. The grain size was estimated by scanning electron microscope. The room temperature dielectric and magnetic properties were studied in the frequency range (100 kHz–1.8 GHz). The magnetization properties were measured upto 1.5 T. The acoustic emission has been measured along the hysteresis loops from 80 K to Curie temperature. It is found that the magneto-acoustic emission (MAE) activity along hysteresis loop is proportional to the hysteresis losses during the same loop. This law has been verified on series of polycrystalline ferrites and found that the law is valid whatever the composition, the grain size and temperature. It is also found that the domain wall creation/or annihilation processes are the origin of the MAE.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Effect of additions of coarse grains and fibers on the densification of a sinterable SiC

This note reports the effects on densification of independent additions of coarse equiaxed SiC grains and fibrous SiC that were mixed with fine beta-SiC to develop a duplex microstructure with improved toughness. The fine-matrix SiC did not contain excess boron and carbon. The equiaxed CVD beta-SiC was introduced in the fine beta-SiC matrix material in amounts of 5 and 10 wt%. Results indicate that the CVD beta-SiC, which is quite coarse, exhibits little indication of sinterability. The effect of these coarse-grained and fibrous additions on the sinterability of fine beta-SiC may result from a geometric type of interaction. This interpretation is reinforced by X-ray diffraction of the powders and sintered pellets via monochromatic CuK-alpha radiation; the diffraction patterns of the sintered composite structures are virtually a combination of those of the components. The addition of nonsinterable SiC to the sinterable material slightly reduces sinterability, the larger particles interacting geometrically with the fine matrix material to prevent complete densification.

Abe, H.↗
DOE OSTI2017

Formation of sodium bismuth titanate-barium titanate during solid-state synthesis

Phase formation of sodium bismuth titanate (Na 0.5 Bi 0.5 TiO 3 or NBT) and its solid solution with barium titanate (BaTiO 3 or BT) during the calcination process is studied using in situ high-temperature diffraction. The reactant powders were mixed and heated to 1000°C, while X-ray diffraction patterns were recorded continuously. Phase evolutions from starting materials to final perovskite products are observed, and different transient phases are identified. The formation mechanism of NBT and NBT–xBT perovskite structures is discussed, and a reaction sequence is suggested based on the observations. The in situ study leads to a new processing approach, which is the use of nano-TiO 2 , and gives insights to the particle size effect for solid-state synthesis products. Lastly, it was found that the use of nano-TiO 2 as reactant powder accelerates the synthesis process, decreases the formation of transient phases, and helps to obtain phase-pure products using a lower thermal budget.

36 MATERIALS SCIENCE↗
DOE OSTI2025

An experimental and computational investigation of the structure and spectroscopic signatures of α -UO 3

α-UO 3 is a common intermediate compound found in the nuclear fuel cycle, yet the exact crystal structure of this material has long been debated. Inconsistent computational and experimental data in previous works has led to varying conclusions between authors. Furthermore, to ensure the validity of our results in this work, the structural and spectroscopic signatures of pure phase α-UO 3 are investigated using powder X-ray diffraction and optical vibrational spectroscopy (infrared and Raman). Rietveld refinement of powder X-ray diffraction data on pure phase α-UO 3 collected in this work allows us to propose an alteration to the currently accepted C2mm structure (a = 3.9705 Å, b = 6.8553 Å, c = 4.15955 Å, α = β = γ = 90°) for α-UO 3 with no uranyl [UO 2 2+ ] bonds. Raman spectra collected using two excitation wavelengths (two instruments using 532 nm and one 785 nm) are presented, and differences with recently published results are discussed. Infrared spectra from two instruments used here agree well with recently published results, but the spectral range encompassed in our data extends past what has been reported with modern techniques. Additionally, we provide tentative vibrational mode assignments based on density functional perturbation theory calculations and resulting phonon eigenvector visualizations. Unexpected features in the optical vibrational spectra of α-UO 3 are explained by unique features in the structure we present.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2015

Two-dimensional inorganic–organic hybrid semiconductors composed of double-layered ZnS and monoamines with aromatic and heterocyclic aliphatic rings: Syntheses, structures, and properties

As an addition to the II–VI based inorganic–organic hybrid semiconductor family, five new two-dimensional (2D) double-layered structures have been synthesized employing monoamines with different aromatic or heterocyclic aliphatic rings. Zn{sub 2}S{sub 2}(bza) (1), Zn{sub 2}S{sub 2}(mbza) (2), Zn{sub 2}S{sub 2}(fbza) (3), Zn{sub 2}S{sub 2}(pca) (4), and Zn{sub 2}S{sub 2}(thfa) (5) (bza=benzylamine, mbza=4-methoxybenzylamine, fbza=4-flurobenzylamine, pca=3-picolylamine, and thfa=tetrahydrofurfurylamine) are prepared by solvothermal reactions and characterized by different analytical methods, including powder X-ray diffraction, optical diffuse reflection, thermogravimetric analysis and photoluminescence spectroscopy. The powder X-ray diffraction patterns show that all five compounds adopt 2D double-layered structures. Optical diffuse reflectance spectra of these compounds suggest that they have notably lower band gaps than those of the similar compounds composed of aliphatic alkyl amines. Their photoluminescence properties and thermal stability are also analyzed. - Graphical abstract: Five new members of two-dimensional double-layered 2D-Zn{sub 2}S{sub 2}(L) (L=Ligand) structures employing monoamines with different aromatic or heterocyclic aliphatic rings have been designed, synthesized, and characterized. - Highlights: • A new sub-family of II-VI based hybrid semiconductors are designed, synthesized, and structurally characterized using amines with aromatic or aliphatic cyclic rings. • These compounds have notably lower band gaps than those made of aliphatic alkyl amines, greatly broadening the range of band gaps of this material family. • They emit strongly with systematically tunable emission intensity and energy.

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

IrGe 4 : A Predicted Weyl-Metal with a Chiral Crystal Structure

Polycrystalline IrGe4 was synthesized by annealing elements at 800 °C for 240 h, and the composition was confirmed by energy-dispersive X-ray spectroscopy. IrGe 4 adopts a chiral crystal structure (space group P3 1 21) instead of a polar crystal structure (P3 1 ), which was corroborated by the convergent-beam electron diffraction and Rietveld refinements using synchrotron powder X-ray diffraction data. The crystal structure features layers of IrGe 8 polyhedra along the b axis, and the layers are connected by edge- and corner-sharing. Each layer consists of corner-shared [Ir 3 Ge 20 ] trimers, which are formed by three IrGe 8 polyhedra connected by edge-sharing. Temperature-dependent resistivity indicates metallic behavior. The magnetoresistance increases with increasing applied magnetic field, and the nonsaturating magnetoresistance reaches 11.5% at 9 T and 10 K. The Hall resistivity suggests that holes are the majority carrier type, with a carrier concentration of 4.02 × 10 21 cm –3 at 300 K. In conclusion, electronic band structures calculated by density functional theory reveal a Weyl point with a chiral charge of +3 above the Fermi level.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗