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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Optimized in situ crystal growth and disordered quasi-one-dimensional magnetism in Li 2 Mn 2 ( MoO 4 ) 3

We present that the quasi-one-dimensional structure of Li 2 Mn 2 ( MoO 4 ) 3 consists of three mutually distinct chains of Li 1 - x Mn x -centered polyhedra in which Mn ostensibly adopts a J = 5 / 2 Mn 2 + configuration. In situ x-ray scattering experiments carried out as crystallites emerge from a molten oxide solution facilitate the synthesis of large single crystals. Ex situ x-ray diffraction finds no evidence of long-range Li/Mn occupancy ordering, suggesting that the structure is effectively composed of finite chains of Mn moments of statistically varying lengths. UV/visible diffuse reflectance spectroscopy measurements establish a wide 3.43(12)-eV direct charge gap consistent with the local polyhedral coordination of the nominally Mn 2 + species. The temperature T dependence of the DC magnetic susceptibility χ reveals a fluctuating moment of only 2.74 μ B ± 0.01 μ B /Mn, dramatically reduced from the 5.9 μ B /Mn expected for Mn 2 + . Meanwhile, the Weiss temperature Θ W = - 89 ± 1 K reveals antiferromagnetic fluctuations that are stymied from reaching an ordered state apparently by the chemical disorder intrinsic to the polyhedral chains. Measurements of magnetization vs field H at T ≤ 10 K are far from saturation even at H = 5 T and are strongly non-Brillouin-like, instead scaling as H / T 0.24 ( 3 ) and suggesting the presence of quantum fluctuations associated with an eventual quasi-one-dimensional, disordered magnetic phase.

1-dimensional systems↗
DOE OSTI2021

Conduction via surface states in antiferromagnetic Mott-insulating Ni S 2 single crystals

Pyrite structure transition-metal disulfides exhibit diverse ground states vs d-band filling, spanning diamagnetic semiconducting, ferromagnetic metallic, antiferromagnetic Mott insulating, and superconducting in FeS 2 , CoS 2 , NiS 2 , and CuS 2 . NiS is particularly interesting and poorly understood as its Mott insulating behavior is accompanied by complex antiferromagnetic ordering below ~38 K and perplexing weak ferromagnetism below ~30 K. Temperature-, pressure-, and composition-dependent insulator-metal transitions also occur, particularly in bandwidth-controlled NiS 2–x Se x , hole-doped Ni 1–x Co x S 2 , etc. Here, we use high-quality chemical-vapor-transport-grown NiS 2 single crystals characterized by x-ray diffraction, energy-dispersive x-ray spectroscopy, magnetometry, and extensive transport and magnetotransport measurements, to generate new insight into this system. In particular, resistivity, magnetoresistance, and Hall effect analyses vs temperature, thickness, and surface preparation, provide unequivocal evidence of surface conduction, where the more conductive surface shunts essentially all current at low temperatures. The surface transport changes from two dimensional and insulating to three dimensional and metallic as the surface preparation is varied (also displaying intriguing sensitivity to magnetic ordering), significantly clarifying literature ambiguities with respect to the electronic ground state. These results have immediate implications. First, the temperature-, pressure-, and composition-dependent insulator-metal transitions deduced in the extensive prior work on NiS 2-x Se x , Ni 1–x Co x S 2 , etc., must clearly be reexamined in light of rife metallic surface conduction, not previously taken into account. Second, NiS 2 now joins FeS 2 and CoS 2 as systems in which bulk and surface electronic behaviors are strikingly different, suggesting that metallic surface states could be a universal feature of pyrite structure transition-metal disulfides.

36 MATERIALS SCIENCE↗
DOE OSTI2015

New scientific equipment for protein crystallization in microgravity, BELKA, and its approbation on the Bion-M No. 1 spacecraft

A space experiment on the crystallization of lisozyme and glucose isomerase proteins in UK-1 and UK-2 crystallizers on the scientific equipment BELKA on the Bion-M no. 1 spacecraft was performed in April–May 2013. A ground-based experiment was carried out simultaneously at the Institute of Crystallography of the Russian Academy of Sciences (IC RAS). Transparent crystals were obtained in both cases. The lisozyme crystals grown in microgravity are larger than their terrestrial analogs. An optical study of glucose isomerase crystals grown in space has shown that the coalescence of equally oriented crystallites leads to the formation of quasi-single-crystal blocks. An X-ray diffraction experiment on lisozyme crystals has revealed the resolutions for crystals obtained under terrestrial conditions and in space to be 1.74 and 1.58 Å, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth and structure of K{sub 2}Ni{sub x}Co{sub (1–x)}(SO{sub 4}){sub 2} · 6H{sub 2}O single crystals

Single crystals of the K{sub 2}Ni{sub x}Co{sub (1–x)}(SO{sub 4}){sub 2} · 6H{sub 2}O composition are grown by spontaneous flux crystallization. More exact chemical formulas of the single crystals are determined based on the diffraction data as K{sub 2}Co(SO{sub 4}){sub 2} · 6H{sub 2}O (I), K{sub 2}(Co{sub 0.657}Ni{sub 0.343})(SO{sub 4}){sub 2} · 6H{sub 2}O (II), K{sub 2}(Co{sub 0.226}Ni{sub 0.774})(SO{sub 4}){sub 2} · 6H{sub 2}O (III), K{sub 2}(Co{sub 0.216}Ni{sub 0.784})(SO{sub 4}){sub 2} · 6H{sub 2}O (IV), and K{sub 2}Ni(SO{sub 4}){sub 2} · 6H{sub 2}O (V). The substitution of nickel atoms for cobalt atoms in structure I results in a shortening of all (Co,Ni)–O interatomic distances. With increasing Ni concentration, the (Co,Ni)–O2 distance shortens to a lesser degree than the (Co,Ni)–O1 and (Co,Ni)–O3 distances and, as a consequence, the distortion of (Co,Ni)O{sub 6} octahedra decreases. NiO{sub 6} polyhedra are less distorted than CoO{sub 6} octahedra. The analysis of difference syntheses of electron density shows that the number of uninterpretable peaks on the maps of mixed crystals II, III, and IV, as well as on the map of K{sub 2}Co(SO{sub 4}){sub 2} · 6H{sub 2}O, is larger with respect to those of structure K{sub 2}Ni(SO{sub 4}){sub 2} · 6H{sub 2}O.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis, Crystal Structure, Electrochemical Properties, and Biological Activity of 2-((1H-Benzimidazol-2-yl)methylamino)acetic Acid

A water soluble compound, (2-((1H-benzimidazol-2-yl)methylamino)acetic acid, BIGH, has been synthesized and structurally characterized by elemental analysis, IR and UV spectroscopies, {sup 1}H-NMR, thermogravimetric and differential thermal analyses, and single crystal and powder X-ray diffraction. BIGH can act as a flexible planar ligand with three potential coordination sites. It crystallizes in a monoclinic system with the sp. gr. P2{sub 1}/c with the unit cell parameters, a = 9.3764(7) Å, b = 11.5031(8) Å, c = 10.0543(6) Å, and Z = 4. The crystal structure was stabilized through inter-molecular hydrogen bonds. The anti-microbial activity of the compound has been studied against Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and Staphylococcus aureus, which showed a good activity against Bacillus subtilis. Cyclic voltammogram of the compound shows that it is a redox-active molecule.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Synthesis and structural characterization of orthorhombic Cu 3– δ Sb ( δ ≈ 0.1) and hexagonal Cu 3 Sb 1–x In x (x ≈ 0.2) phases

Cu 3 Sb is a known copper-rich phase in the Cu–Sb binary phase diagram. It is reported to be dimorphic, with a low-temperature form adopting the orthorhombic Cu 3 Ti structure type (space group Pmmn , No. 59). The high-temperature form crystallizes in the cubic space group F m 3 - m $Fm‾{3}m$ (No. 225), and is isostructural with BiF 3 . Neither polymorph has been carefully characterized to date, with both structures being assigned to the respective structure type, but never refined. With this study, we provide structural evidence, based on single-crystal and powder X-ray diffraction data that the low-temperature orthorhombic phase exists with a significant amount of defects on one of the Cu-sites. As a result, its composition is not Cu 3 Sb, but rather Cu 3– δ Sb ( δ = 0.13(1)). The cubic form could not be accessed as a part of this study, but another Cu-rich phase, Cu 3 Sb ≈0.8 In ≈0.2 , was also identified. It adopts the hexagonal Ni 3 Sn structure type (space group P 6 3 / mmc , No. 194) and represents an In-substituted variant of a hitherto unknown structural modification of Cu 3 Sb. Whether the latter can exist as a binary phase, or what is the minimum amount of In inclusions needed to stabilize it remains to be determined. Measurements of the thermopower of Cu 3– δ Sb ( δ = 0.13(1)) were conducted in the range of 300–600 K and demonstrated a maximum value of ca. 50 μV/K at 600 K, indicative of a p -type transport mechanism. Electrical resistivity measurements for the same sample confirmed that it exhibits metallic-like behavior, with a room temperature value of 0.43 mΩ cm. Electronic structure calculations show the absence of a band gap. Thermal analysis was utilized to ascertain the congruent melting of both phases.

Crystallography↗
DOE OSTI2015

Actinide Research Quarterly: First Quarter 2015

The Seaborg Institute welcomes Brian L. Scott as guest editor for this special Actinide Research Quarterly issue showcasing the rich science and history of the crystallography of actinides. A staff scientist at Los Alamos National Laboratory, Brian has extensive experience in structure determination using single-crystal and powder x-ray diffraction techniques. He has explored molecular and solid-state structures in a variety of materials ranging from bioinorganic molecules to plutonium-based superconductors. His interests include structural inorganic chemistry and the synthesis and characterization of actinide-containing materials important to understanding f-orbital bonding and reactivity. He has authored over 350 papers, with more than 8,000 citations.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Oval-cycloidal Magnetic Structure with Phase-shift in the Non-centrosymmetric Tetragonal Compound CePdSi 3

CePdSi 3 with H // [100] exhibits multiple metamagnetic transitions. Since there is no frustration in this system, it is suggested that the origin of the multiple metamagnetic transitions is the influence of the antisymmetric spin–orbit interaction. To clarify the magnetic structure under the influence of the antisymmetric spin–orbit interaction, neutron diffraction experiments have been performed using single crystal samples of CePdSi3. There are observed magnetic reflections with incommensurate magnetic propagation vector q=(0.315,0,0) in the phase I. In addition, additional magnetic reflections were also observed in the phase III. The magnetic structure was found to be an oval-cycloidal structure at the phase III in CePdSi 3 , and we discuss the origin of the unusual magnetic structure.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Finding a New B1-Type Phase in Single Crystals of Fe–Al and Fe–Ga Soft Magnetic Alloys

The atomic structure of Fe–Al (7 and 9 at % Al) and Fe–Ga (18 at % Ga) alloys is studied by X‑ray diffraction using a laboratory four-circle diffractometer. After refining annealing, single-crystal alloy samples were annealed in the ferromagnetic state (T < T{sub C}). One sample of the Fe–18 at % Ga alloy, after short holding in the paramagnetic state (T > T{sub C}), was quenched in room temperature water. Earlier, the authors reported on the peculiarities of the ordering of alloying atoms in B2 and D0{sub 3} phase structures in quenched and annealed samples of these alloys. Here, we present and discuss the results of our observations in these alloys of a new phase with a face-centered cubic (fcc) lattice (B1-type structure with NaCl prototype and unit cell parameter ~5.2 nm). The fcc phase appears in the Fe–Al alloy as the aluminum concentration increases from 7 to 9 at %; it is observed in the Fe–18 at % Ga alloy, and its volume fraction increases after annealing in the ferromagnetic state in comparison with a quenched alloy sample. In these alloys (9 at % Al) and (18 at % Ga), different ways of embedding fcc crystals in the bcc phase of single crystals are realized; i.e., the axes of the fcc lattice are directed in four different ways relative to the axes of the bcc lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

High-order harmonics and the reverse of the squaring up process in the triangular-lattice magnet HoPdAl 4 ⁢Ge 2

We uncover high-order harmonics and the reverse of the squaring-up process, in terms of analyzing the evolution of magnetic orders in a centrosymmetric layered triangular-lattice magnet HoPdAl 4 ⁢Ge 2 , based on a detailed study of the crystal structure, magnetic susceptibility, magnetization, heat capacity, and magnetic structure. Temperature dependencies of magnetic susceptibility and heat capacity show two magnetic transitions at T N = 10.5 K and T t = 5.5 K. Below T N , Ho 3+ spins order antiferromagnetically as a transverse spin-density wave with the propagation vector k 1 = (001.5 – δ) with δ ≈ 0.18. Upon further cooling through T t , the high-order harmonics with k n = (001.5 – nδ), n = 3, 5, 7 develop, suggesting a squaring-up process. It is surprising that the squaring-up process does not continue down to 0 K but reverses the trend below 3 K. Magnetic-field-induced metastable transitions were observed in M⁡(H) curves with the fields applied both parallel and perpendicular to the triangular-lattice plane. Neutron-diffraction results suggest that the magnetization process in HoPdAl 4 ⁢Ge 2 involves the conversion of k n = (001.5 – n⁢δ) with n = 1, 3, 5, 7, to a ferromagnetic k F = (000) component. It is worth noting that the already weak seventh harmonic magnetic peak is enhanced by applying a small magnetic field in the ab plane at 1.5 K or warming up to 3 K, accompanied by a slight decrease of δ.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Single Hit Energy-resolved Laue Diffraction

In situ white light Laue diffraction has been successfully used to interrogate the structure of single crystal materials undergoing rapid (nanosecond) dynamic compression up to megabar pressures. However, information on strain state accessible via this technique is limited, reducing its applicability for a range of applications. Here, we present an extension to the existing Laue diffraction platform in which we record the photon energy of a subset of diffraction peaks. This allows for a measurement of the longitudinal and transverse strains in situ during compression. Consequently, we demonstrate measurement of volumetric compression of the unit cell, in addition to the limited aspect ratio information accessible in conventional white light Laue. We present preliminary results for silicon, where only an elastic strain is observed. VISAR measurements show the presence of a two wave structure and measurements show that material downstream of the second wave does not contribute to the observed diffraction peaks, supporting the idea that this material may be highly disordered, or has undergone large scale rotation.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

T d to 1 T' structural phase transition in the WTe 2 Weyl semimetal

Elastic neutron scattering on a single crystal combined with powder x-ray diffraction measurements were carried out to investigate how the crystal structure evolves as a function of temperature in the Weyl semimetal WTe 2 . Here, a sharp transition from the low-temperature orthorhombic phase T d to the high-temperature monoclinic phase 1T' was observed at ambient pressure in the single crystal near ~565 K. Unlike in MoTe 2 , the solid-solid transition from T d to 1T' occurs without the cell doubling of the intermediate T d * phase with AABB (or ABBA) layer stacking. In powders, however, the thermal transition from the Td to the 1T' phase was broadened and a two-phase coexistence was observed until 700 K, well above the structural transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

X-ray crystallographic studies of the extracellular domain of the first plant ATP receptor, DORN1, and the orthologous protein from Camelina sativa

Does not respond to nucleotides 1 (DORN1) has recently been identified as the first membrane-integral plant ATP receptor, which is required for ATP-induced calcium response, mitogen-activated protein kinase activation and defense responses in Arabidopsis thaliana . In order to understand DORN1-mediated ATP sensing and signal transduction, crystallization and preliminary X-ray studies were conducted on the extracellular domain of DORN1 (atDORN1-ECD) and that of an orthologous protein, Camelina sativa lectin receptor kinase I.9 (csLecRK-I.9-ECD or csI.9-ECD). A variety of deglycosylation strategies were employed to optimize the glycosylated recombinant atDORN1-ECD for crystallization. In addition, the glycosylated csI.9-ECD protein was crystallized at 291 K. X-ray diffraction data were collected at 4.6 Å resolution from a single crystal. The crystal belonged to space group C 222 or C 222 1 , with unit-cell parameters a = 94.7, b = 191.5, c = 302.8 Å. These preliminary studies have laid the foundation for structural determination of the DORN1 and I.9 receptor proteins, which will lead to a better understanding of the perception and function of extracellular ATP in plants.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Femtosecond time-resolved MeV electron diffraction

We report the experimental demonstration of femtosecond electron diffraction using high-brightness MeV electron beams. High-quality, single-shot electron diffraction patterns for both polycrystalline aluminum and single-crystal 1T-TaS 2 are obtained utilizing a 5 fC (~3 × 10 4 electrons) pulse of electrons at 2.8 MeV. The high quality of the electron diffraction patterns confirms that electron beam has a normalized emittance of ~50 nm rad. The transverse and longitudinal coherence length is ~11 and ~2.5 nm, respectively. The timing jitter between the pump laser and probe electron beam was found to be ~100 fs (rms). The temporal resolution is demonstrated by observing the evolution of Bragg and superlattice peaks of 1T-TaS 2 following an 800 nm optical pump and was found to be 130 fs. Lastly, our results demonstrate the advantages of MeV electrons, including large elastic differential scattering cross-section and access to high-order reflections, and the feasibility of ultimately realizing below 10 fs time-resolved electron diffraction.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Chiral properties of the zero-field spiral state and field-induced magnetic phases of the itinerant kagome metal YMn 6 Sn 6

Applying a magnetic field in the hexagonal plane of YMn 6 Sn 6 leads to a complex magnetic phase diagram of commensurate and incommensurate phases, one of which coexists with the topological Hall effect (THE) generated by a unique fluctuation-driven mechanism. Using unpolarized neutron diffraction, we report on the solved magnetic structure for two previously identified, but unknown, commensurate phases. These include a low-temperature, high-field fanlike phase and a room-temperature, low-field canted antiferromagnetic phase. Here, an intermediate incommensurate phase between the fanlike and forced ferromagnetic phases is also identified as the last known phase of the in-plane field-temperature diagram. Additional characterization using synchrotron powder diffraction reveals extremely high-quality, single-phase crystals, which suggests that the presence of two incommensurate magnetic structures throughout much of the phase diagram is an intrinsic property of the system. Interestingly, polarized neutron diffraction shows that the centrosymmetric system hosts preferential chirality in the zero-field double-flat-spiral phase, which, along with the THE, is a topologically nontrivial characteristic.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Single crystal structure analysis of a single Sm{sub 2}Fe{sub 17}N{sub 3} particle

We performed single crystal structure analysis of Sm{sub 2}Fe{sub 17}N{sub 3} using X-ray diffraction. A pick-up system combined with a micromanipulation tool driven by piezoelectric actuators and a microgripper was used. A single Sm{sub 2}Fe{sub 17}N{sub x} particle with the diameter of about 20 μm was picked up, and X-ray diffraction was measured using an X-ray diffractometer at the synchrotron radiation beamline at the Photon Factory, KEK. Single crystal structure analysis of a Sm{sub 2}Fe{sub 17}N{sub 3} particle was performed and the structure was successfully determined from X-ray diffraction patterns. The space group and the lattice constants were determined to be R-3m (number sign166) a = b = 8.7206 Å and c = 12.6345 Å, respectively. Atomic positions of Sm and Fe atoms were accurately determined by single crystal structure analysis of only one particle.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Growth and microtopographic study of CuInSe{sub 2} single crystals

The CuInSe{sub 2} single crystals were grown by chemical vapour transport (CVT) technique using iodine as transporting agent. The elemental composition of the as-grown CuInSe{sub 2} single crystals was determined by energy dispersive analysis of X-ray (EDAX). The unit cell crystal structure and lattice parameters were determined by X-ray diffraction (XRD) technique. The surface microtopographic study of the as-grown CuInSe{sub 2} single crystals surfaces were done to study the defects, growth mechanism, etc. of the CVT grown crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural and Crystal Chemical Properties of Alkali Rare-earth Double Phosphates

When appropriately activated, alkali rare-earth double phosphates of the form: M 3 RE(PO 4 ) 2 (where M denotes an alkali metal and RE represents either a rare-earth element or Y or Sc) are of interest for use as inorganic scintillators for radiation detection at relatively long optical emission wavelengths. These compounds exhibit layered crystal structures whose symmetry properties depend on the relative sizes of the rare-earth and alkali-metal cations. Single-crystal X-ray and powder neutron diffraction methods were used here to refine the structures of the series of rare-earth double phosphate compounds: K 3 RE(PO 4 ) 2 with RE = Lu, Er, Ho, Dy, Gd, Nd, Ce, plus Y and Sc - as well as the compounds: A 3 Lu(PO 4 ) 2 , with A = Rb, and Cs. The double phosphate K 3 Lu(PO 4 ) 2 was reported and structurally refined previously. This material had a hexagonal unit cell at room temperature with the Lu ion six-fold coordinated with oxygen atoms of the surrounding phosphate groups. Additionally two lower-temperature phases were observed for K 3 Lu(PO 4 ) 2 . The first phase transition to a monoclinic P21/m phase occurred at ~230 K, and the Lu ion retained its six-fold coordination. The second K 3 Lu(PO 4 ) 2 phase transition occurred at ~130 K. The P21/m space group symmetry was retained, however, one of the phosphate groups rotated to increase the oxygen coordination number of Lu from six to seven. This structure then became isostructural with the room-temperature form of the compound K 3 Yb(PO 4 ) 2 reported here that also exhibits an additional high-temperature phase which occurs at T = 120 °C with a transformation to hexagonal P-3 space group symmetry and a Yb-ion coordination number reduction from seven to six. This latter result was confirmed using EXAFS. The single-crystal growth methods structural systematics, and thermal expansion properties of the present series of alkali rare-earth double phosphates, as determined by X-ray and neutron diffraction methods, are treated here.

36 MATERIALS SCIENCE↗