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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

X-ray diffraction at the National Ignition Facility

We report details of an experimental platform implemented at the National Ignition Facility to obtain in situ powder diffraction data from solids dynamically compressed to extreme pressures. Thin samples are sandwiched between tamper layers and ramp compressed using a gradual increase in the drive-laser irradiance. Pressure history in the sample is determined using high-precision velocimetry measurements. Up to two independently timed pulses of x rays are produced at or near the time of peak pressure by laser illumination of thin metal foils. The quasi-monochromatic x-ray pulses have a mean wavelength selectable between 0.6 Å and 1.9 Å depending on the foil material. The diffracted signal is recorded on image plates with a typical 2 θ x-ray scattering angle uncertainty of about 0.2° and resolution of about 1°. Analytic expressions are reported for systematic corrections to 2 θ due to finite pinhole size and sample offset. A new variant of a nonlinear background subtraction algorithm is described, which has been used to observe diffraction lines at signal-to-background ratios as low as a few percent. Variations in system response over the detector area are compensated in order to obtain accurate line intensities; this system response calculation includes a new analytic approximation for image-plate sensitivity as a function of photon energy and incident angle. This experimental platform has been used up to 2 TPa (20 Mbar) to determine the crystal structure, measure the density, and evaluate the strain-induced texturing of a variety of compressed samples spanning periods 2–7 on the periodic table.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Fleetite, Cu 2 RhIrSb 2 , a New Species of Platinum-Group Mineral from the Miass Placer Zone, Southern Urals, Russia

Fleetite, Cu 2 RhIrSb 2 , a new species of platinum-group mineral (PGM), was discovered intergrown with an Os–Ir–Ru alloy in the Miass Placer Zone (Au–PGE), southern Urals, Russia. A single grain 50 μm across was found. Osmium, ruthenium, and iridium are the main associated minerals; also present are Pt–Fe alloys, laurite, Sb-rich irarsite, Rh-rich tolovkite, kashinite, anduoite, ferronickelplatinum, heazlewoodite, PGE-bearing pentlandite and digenite, as well as micrometric inclusions of forsterite (Fo 93.7 ), chromite–magnesiochromite, and Mg-rich edenite. In reflected light, fleetite is light gray; it is opaque, isotropic, non-pleochroic, and non-bireflectant. We report reflectance values measured in air. A mean of seven point-analyses (wavelength-dispersive spectrometry) gave Cu 13.93, Ni 8.60, Fe 0.10, Ir 28.07, Rh 7.91, Ru 1.96, Sb 39.28, total 99.85 wt.%, corresponding to (Cu 1.41 Ni 0.58 Fe 0.01 ) Σ2.00 (Rh 0.49 Ni 0.36 Ru 0.12 ) Σ0.97 Ir 0.95 Sb 2.08 on the basis of six atoms per formula unit, taking into account the structural results. The calculated density is 10.83 g/cm 3 . Single-crystal X-ray studies show that fleetite is cubic, space group Fdm (#227), a = 11.6682(8) Å, V = 1588.59(19) Å 3 , and Z = 16. A least-squares refinement of X-ray powder-diffraction data gave a = 11.6575(5) Å and V = 1584.22(19) Å 3 . The strongest five reflections in the powder pattern [d in Å(I)(hkl)] are: 6.70(75)(111), 4.13(100)(220), 3.52(30)(311), 2.380(50)(422), 2.064(40)(440). Results of synchrotron micro-Laue diffraction experiments are consistent [a = 11.66(2) Å]. The crystal structure of fleetite was solved and refined to R = 0.0340 based upon 153 reflections with F o > 4σ(F o ). It is isotypic with Pd 11 Bi 2 Se 2 and best described as intermetallic, with all metal atoms in 12-fold coordination. Fleetite and other late exotic phases were formed by reaction of the associated alloy phases with a fluid phase enriched in Sb, As, and S in circulation in the cooling ophiolite source-rock. The mineral is named after Michael E. Fleet (1938–2017) in recognition of his significant contributions to the Earth Sciences.

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

Exact and fast calculation of the X-ray pair distribution function

A fast and exact algorithm to calculate the powder pair distribution function (PDF) for the case of periodic structures is presented. The new algorithm calculates the PDF by a detour via reciprocal space. The calculated normalized total powder diffraction pattern is transferred into the PDF via the sine Fourier transform. The calculation of the PDF via the powder pattern avoids the conventional simplification of X-ray and electron atomic form factors. It is thus exact for these types of radiation, as is the conventional calculation for the case of neutron diffraction. The new algorithm further improves the calculation speed. Additional advantages are the improved detection of errors in the primary data, the handling of preferred orientation, the ease of treatment of magnetic scattering and a large improvement to accommodate more complex instrumental resolution functions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Unique edge-sharing sulfate-transition metal coordination in Na{sub 2}M(SO{sub 4}){sub 2} (M=Ni and Co)

Two compounds, Na{sub 2}Ni(SO{sub 4}){sub 2} and Na{sub 2}Co(SO{sub 4}){sub 2}, were synthesized and their structure and properties were characterized. They adopt a structure that contains a bidentate coordination of sulfate to the transition metal center, which was determined via single crystal X-ray diffraction combined with model refinements to both laboratory X-ray and time-of-flight neutron powder diffraction data. The compounds were both found to crystallize in the C2/c space group with Z=24 and a unit cell of a=23.3461(3) Å, b=10.3004(1) Å, c=17.4115(2) Å, β=98.8659(9)°, and V=4136.99(8) Å{sup 3} for the cobalt analog and a=23.2253(1) Å, b=10.26155(6) Å, c=17.3353(1) Å, β=99.0376(5)°, and V=4080.20(5) Å{sup 3} for the nickel analog. Magnetization measurements show that the transition metal centers have negligible interactions with neighboring sites. Infrared and Raman spectroscopies were used to further probe the unique sulfate-transition metal coordination, and confirm the bidentate binding motif. The resulting pseudo-trigonal bipyramidal coordination produces vivid violet, Na{sub 2}Co(SO{sub 4}){sub 2}, and yellow, Na{sub 2}Ni(SO{sub 4}){sub 2}, colors that were probed by diffuse reflectance. - Graphical abstract: Two blue distorted transition metal octahedra (oxygen in red) bridged by two sulfate tetrahedra are shown here. Each bridging sulfate tetrahedra shares an edge with one octahedron and a corner with the other. All of the remaining corners of the octahedra are corner sharing with four tetrahedra forming a polyhedral network. - Highlights: • Structure of Na2Ni(SO4)2 and Na2Co(SO4)2 is determined. • Unique sulfate-transition metal binding observed in the new structure. • Combined diffraction and spectroscopic techniques were used. • Magnetization measurements show negligible interactions between sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

X-Ray Diffraction on NIF

The National Ignition Facility (NIF) is currently a 192 beam, 1.6 MJ laser. NIF Ramp-Compression Experiments have already made the relevant exo-planet pressure range from 1 to 50 Mbar accessible. We Proposed to Study Carbon Phases by X-Ray Diffraction on NIF. Just a few years ago, ultra-high pressure phase diagrams for materials were very 'simple'. New experiments and theories point out surprising and decidedly complex behavior at the highest pressures considered. High pressures phases of aluminum are also predicted to be complex. Recent metadynamics survey of carbon proposed a dynamic pathway among multiple phases. We need to develop diagnostics and techniques to explore this new regime of highly compressed matter science. X-Ray Diffraction - Understand the phase diagram/EOS/strength/texture of materials to 10's of Mbar. Strategy and physics goals: (1) Powder diffraction; (2) Begin with diamond; (3) Continue with metals etc.; (4) Explore phase diagrams; (5) Develop liquid diffraction; and (6) Reduce background/improve resolution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Neutron diffraction study of the monoclinic to tetragonal structural transition in LaNbO{sub 4} and its relation to proton mobility

The fergusonite-scheelite structural transition of LaNbO{sub 4} was characterized by high-intensity variable temperature neutron powder diffraction in an effort to link structural changes to proton transport in the low temperature monoclinic and high temperature tetragonal polymorphs. The pronounced decrease in enthalpy of proton mobility with increasing temperature in monoclinic LaNbO{sub 4}, identified by Fjeld et al. , was found to coincide with the decrease in a key inter-tetrahedral oxygen separation. At temperatures above the transition, this oxygen to oxygen distance remains constant, behavior that is consistent with the invariant nature of the calculated enthalpy of mobility for the tetragonal phase. This oxygen separation is therefore proposed as the key structural parameter determining the success rate of proton transfer and ultimately the proton diffusion in LaNbO{sub 4}. Infrared measurements performed on acceptor-doped LaNbO{sub 4} show an absorption in the region 2500 to 3700 cm{sup -1} attributed to the O-H stretching motion influenced by hydrogen bonding. - Graphical Abstract: The structural phase transition from monoclinic fergusonite to tetragonal scheelite crystal structure clearly influences the proton conductivity of acceptor-doped LaNbO{sub 4} (see Figure). The present article attempts to explain why. Highlights: Black-Right-Pointing-Pointer Transition from monoclinic to tetragonal structure studied using neutron diffraction. Black-Right-Pointing-Pointer Change in proton mobility linked to contraction of a key oxygen separation. Black-Right-Pointing-Pointer Infra-red spectra reveal intermediate strength hydrogen bonding.

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

In-situ mechanical testing during X-ray diffraction

Deforming metals during recording X-ray diffraction patterns is a useful tool to get a deeper understanding of the coupling between microstructure and mechanical behaviour. With the advances in flux, detector speed and focussing techniques at synchrotron facilities, in-situ mechanical testing is now possible during powder diffraction and Laue diffraction. The basic principle is explained together with illustrative examples.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Crystal structure and magnetic properties of novel R{sub 3}Co{sub 2.2}Si{sub 1.8} compounds (R=Y, Gd-Tm)

The crystal structure of new ternary Dy{sub 3}Co{sub 2.2}Si{sub 1.8} compound has been established using single crystal X-ray diffraction, and those of R{sub 3}Co{sub 2.2}Si{sub 1.8} phases (R=Y, Gd-Tm) phases have been verified through the powder diffraction techniques. The Dy{sub 3}Co{sub 2.2}Si{sub 1.8} structure is a new structure type, which is obtained from the Er{sub 3}Ge{sub 4} with an ordered Er{sub 3}Ge{sub 4}-type structure (space group Cmcm) one by coloring the two Ge sites, 4a and 4c, with Si and the 8f site with Co atoms. Tb{sub 3}Co{sub 2.2}Si{sub 1.8}, Dy{sub 3}Co{sub 2.2}Si{sub 1.8}, Ho{sub 3}Co{sub 2.2}Si{sub 1.8} and Er{sub 3}Co{sub 2.2}Si{sub 1.8} compounds display ferromagnetic-type ordering. - Graphical abstract: The novel R{sub 3}Co{sub 2.2}Si{sub 1.8} compounds (R=Y, Gd-Tm) adopt the new structure type, the ordered variant of Er{sub 3}Ge{sub 4}-type structure Magnetic studies on {l_brace}Tb, Dy, Ho, Er{r_brace}{sub 3}Co{sub 2.2}Si{sub 1.8} suggest that their magnetic interactions are primarily ferromagnetic in nature. Highlights: Black-Right-Pointing-Pointer The novel {l_brace}Y, Gd-Tm{r_brace}{sub 3}Co{sub 2.2}Si{sub 1.8} compounds adopt the Dy{sub 3}Co{sub 2.2}Si{sub 1.8} structure type, Black-Right-Pointing-Pointer The Dy{sub 3}Co{sub 2.2}Si{sub 1.8} type is ordered variant of Er{sub 3}Ge{sub 4} type structure. Black-Right-Pointing-Pointer {l_brace}Gd-Tm{r_brace}{sub 3}Co{sub 2.2}Si{sub 1.8} compounds are primarily ferromagnetic in nature.

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

Phase relations and structural features in the system Ni-Zn-B

Phase relations for the system Ni-Zn-B have been established in the isothermal section at 800 Degree-Sign C based on X-ray powder diffraction and electron microprobe analyses of about 60 samples, which have been prepared by hot pressing of pre-annealed powder compacts of arc-melted master alloys Ni{sub x}B{sub y} and Zn-filings. Six ternary compounds (labeled {tau}{sub 1} to {tau}{sub 6}) were found to exist, which in some cases exhibit considerable mutual solid solubilities mostly as an exchange of Ni-Zn at constant B-content, but in the case of the so-called {tau}-phase {tau}{sub 1}-(Ni{sub 1-x}Zn{sub x}){sub 21}[Zn{sub 1-y-z}{open_square}{sub y}(B{sub 4}){sub z}]{sub 2}B{sub 6} (0.07{<=}x{<=}0.11, 0.07{<=}y{<=}0.53, 0{<=}z{<=}0.3) also with Zn/B substitution. Single crystal X-ray data analysis for the composition x=0.07, y=0.125, z=0.30, and a=1.05800(3) nm confirmed the Cr{sub 23}C{sub 6} type with space group Fm3{sup Macron }m, but revealed partial replacement of Zn-atoms by B{sub 4}-tetrahedra (R{sub F}=0.014). Whereas Ni/Zn exchange (at constant B-content) ranges at about 4-5 at% for {tau}{sub 4}-Ni{sub 3}ZnB{sub 2} and {tau}{sub 5}-Ni{sub 48}Zn{sub 32}B{sub 20}, it is below 3 at% for {tau}{sub 2}-Ni{sub 12}ZnB{sub 8-x} (x=0.43), {tau}{sub 3}-Ni{sub 21}Zn{sub 2}B{sub 20} and {tau}{sub 6}-Ni{sub 47}Zn{sub 23}B{sub 30}. The crystal structures of {tau}{sub 2}-Ni{sub 12}ZnB{sub 8-x} (x=0.43; Ni{sub 12}AlB{sub 8} type), {tau}{sub 3}-Ni{sub 21}Zn{sub 2}B{sub 20} (own type) and {tau}{sub 4}-Ni{sub 3}ZnB{sub 2} (own type) have been determined in our foregoing paper [8]. Due to the non-availability of suitable single crystals, the crystal structures of {tau}{sub 5}-Ni{sub 48}Zn{sub 32}B{sub 20} (body-centered orthorhombic; a=1.6(2) nm, b=0.63(7) nm, and c=0.27(0) nm, determined from TEM) and of {tau}{sub 6}-Ni{sub 47}Zn{sub 23}B{sub 30} have not been elucidated yet. Phase equilibria at 800 Degree-Sign C are dominated by a large three-phase field ({beta}B)+Ni{sub 2}Zn{sub 11}+{tau}{sub 3}, as practically all ternary compounds form at compositions with less than about 50 at% Ni. Furthermore, precise data on atom site distribution and positional parameters have been provided from X-ray single crystal refinements for Ni-borides, for which crystal structures hitherto have only been derived from X-ray diffraction photographs: o-Ni{sub 4}B{sub 3-x} (x=0.19; Pnma, a=1.9665(4) nm, b=0.29852(1) nm, c=0.65750(2) nm; R{sub F}=0.015) and m-Ni{sub 4}B{sub 3} (C2/c, a=0.64356(3) nm, b=0.48867(3) nm, c=0.78267(3) nm, {beta}=103.288(3) Degree-Sign , R{sub F}=0.021). - Graphical abstract: Ni-Zn-B isothermal section at 800 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Phase relations were determined for the system Ni-Zn-B at 800 Degree-Sign C. Black-Right-Pointing-Pointer Existence of six ternary compounds ({tau}{sub 1}-{tau}{sub 6}) has been confirmed at 800 Degree-Sign C. Black-Right-Pointing-Pointer Homogeneity range for {tau}{sub 1} with respect to Ni/Zn and Zn/B at 800 Degree-Sign C has been determined. Black-Right-Pointing-Pointer The crystal structures of {tau}{sub 5}-Ni{sub 48}Zn{sub 32}B{sub 20} from TEM (oI, a=1.6(2) nm, b=0.63(7) nm, and c=0.27(0) nm). Black-Right-Pointing-Pointer Precise data on {tau}{sub 1}-(Ni{sub 1-x}Zn{sub x}){sub 21}[Zn{sub 1-y-z{open_square}y}(B{sub 4}){sub z}]{sub 2}B{sub 6} (0.07{<=}x{<=}0.11, 0.07{<=}y{<=}0.53, 0{<=}z{<=}0.3), o-Ni{sub 4}B{sub 3-x} and m-Ni{sub 4}B{sub 3} have been presented.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of Polyhydroxybutyrate (PHB) Produced by Novel Bacterium Lysinibacillus sphaericus BBKGBS6 Isolated From Soil

The aim of the study was to characterization of polyhydroxybutyrate (PHB) produced by novel bacterium Lysinibacillus sphaericus BBKGBS6 isolated from soil. The present study reports that the strain L. sphaericus BBKGBS6, which was isolated from agricultural soil and is capable of producing PHB. Extraction of PHB was done by solvent extraction method. The results indicated the presence of crotonic acid and confirmed the presence of polyhydroxybutyrate in the sample. The FTIR spectra were observed characteristic absorption bonds for ester and the presence of C=O and C–O were obtained. GCMS results showed the major molecular fragmentation were, 117 m/z (C{sub 5}H{sub 9}O{sub 3}{sup +}), 104 m/z (C{sub 4}H{sub 7}O{sub 3}{sup +}), 74 m/z (C{sub 3}H{sub 6}O{sub 2}{sup +}), 61 m/z (C{sub 2}H{sub 3}O{sub 2}{sup +}), 43 m/z (C{sub 2}H{sub 3}O), 59 m/z (C{sub 2}H{sub 3}O). {sup 1}H and {sup 13}C NMR spectra were recorded using purified samples. The molecular weight of PHB (5.64 × 10{sup 5)} was estimated based on viscosity measurement. Films were prepared by the solvent casting method. The structure of crystalline polymers can be determined or refined through best fitting of X-ray powder diffraction profiles. The procedures provide results grossly in agreement with respect to the confirmation of the chain in the powder but differing significantly on a more detailed scale. Such differences represent an additional reason of interest in performing a new structural study. Differential scanning calorimetric experiments was performed using Universal V4.5A TA Instruments, (m.p. 156.61 °C; ΔH = 28.54 J/g) USIC Dharwad. The crystallinity (X{sub c}) of PHB is calculated as per equation given below X{sub c} = DH{sub f}×100/DH{sub 0}×W. The PHB extracted, PHB Sigma and PHB–TS showed two endothermal peaks in between 140 and 200 °C. The enthalpy of melting (ΔHf) was 28.09 J/g for standard PHB and for extracted one is 56.42 J/g. The glass transition temperature of the sample was 140 °C and amorphous temperature was 176.08 °C. Thermo gravimetric analysis (TGA) is a method of thermal analysis in which changes in physical and chemical properties of materials are measured as a function of increasing temperature (with constant heating rate), or as a function of time (with constant temperature and/or constant mass loss). The decomposition temperature at a 10% level determined by TGA for pure PHB in ScCO{sub 2} at 70 °C and 22 MPa was 293.32 °C. Tensile strength of PHB film (28.23 Mpa) was carried out according to ASTMD 882 using universal testing machine (Model Lx 5, LYOD ISNT). Water vapor transmission rate of PHB film (29 g/m{sup 2}/day) was measured as per ASTM E96-95 and carried out according to the desiccant method. Oxygen transmission rate of PHB film 472.36 (cc/m{sup 2}/day/atm 65% Rh and 27 °C) was measured as per the method of ASTM D-1434-66.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Two unusual 12-connected metal–organic coordination polymers with fcu net

Two new three-dimensional 12-connected metal–organic coordination polymers, [Zn{sub 2}(bptc)(H{sub 2}O)]·C{sub 2}H{sub 5}OH·H{sub 2}O (1) and [Cd{sub 4}(bptc){sub 2}(bbi)(H{sub 2}O)]·H{sub 2}O (2) (H4bptc=biphenyl-2,5,2′,5′-tetracarboxylic acid, bbi=1,1′-(1,4-butanediyl)bis(imidazole)), have been solvothermally synthesized and structurally characterized by single crystal X-ray diffraction analyses. All compounds are also characterized by elemental analyses, IR spectra, thermogravimetric (TG) analyses and X-ray powder diffraction (XRD). Topological analysis indicates that both 1 and 2 are 12-connected frameworks with fcu topology, which are based on cuboid cage and rob-like (Cd3) subunit as 12-connected nodes, respectively. Furthermore, the luminescence properties of the two compounds were discussed in detail. - Graphical abstract: Two new compounds with unusual 12-connected fcu topology display intriguing structural feature, as well as luminescence property. Display Omitted - Highlights: • Two new 3D metal–organic coordination polymers based on biphenyl-2,5,2′,5′-tetracarboxylic acid ligand have been synthesized. • Two compounds exhibit rare 12-connected fcu topology. • Photoluminescent property at room temperature has been investigated.

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

Observation of Vacancies, Faults, and Superstructures in Ln 5 Mo 2 O 12 (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

Among oxide compounds with direct metal–metal bonding, the Y 5 Mo 2 O 12 (A 5 B 2 O 12 ) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral B 2 O 10 dimers arranged in one-dimensional edge-sharing chains along the direction of the metal–metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal–metal bonding have integer oxidation states resulting from the lifting of orbital degeneracy typically induced by the metal–metal bonding. Although a monoclinic C2/m structure has been previously proposed for Ln 5 Mo 2 O 12 (Ln = La–Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown in this paper that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable Mo 2 O 10 and LaO 6 building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1–2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of La 5 Mo 2 O 11.55 and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. Finally, this represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Exploring the behavior of molybdenum diboride (MoB{sub 2}): A high pressure x-ray diffraction study

Investigation of the equation of state of molybdenum diboride (MoB{sub 2}) has been performed to 24.1 GPa using synchrotron radiation angle-dispersive x-ray diffraction techniques (ADXRD) in a diamond anvil cell (DAC) at room temperature. Rietveld refinement of the X-ray powder diffraction data reveals that the rhombohedral structure MoB{sub 2} is stable up to 24.1 GPa. The ADXRD data yield a bulk modulus K{sub 0} = 314(11) GPa with a pressure derivative K{sub 0}{sup ′} = 6.4(1.5). The experimental data are discussed and compared to the results of first-principles calculations. In addition, the compressibility of the unit cell axes (a and c axes) of MoB{sub 2} demonstrates an anisotropic property with pressure increasing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Six-axis multi-anvil press for high-pressure, high-temperature neutron diffraction experiments

We developed a six-axis multi-anvil press, ATSUHIME, for high-pressure and high-temperature in situ time-of-flight neutron powder diffraction experiments. The press has six orthogonally oriented hydraulic rams that operate individually to compress a cubic sample assembly. Experiments indicate that the press can generate pressures up to 9.3 GPa and temperatures up to 2000 K using a 6-6-type cell assembly, with available sample volume of about 50 mm{sup 3}. Using a 6-8-type cell assembly, the available conditions expand to 16 GPa and 1273 K. Because the six-axis press has no guide blocks, there is sufficient space around the sample to use the aperture for diffraction and place an incident slit, radial collimators, and a neutron imaging camera close to the sample. Combination of the six-axis press and the collimation devices realized high-quality diffraction pattern with no contamination from the heater or the sample container surrounding the sample. This press constitutes a new tool for using neutron diffraction to study the structures of crystals and liquids under high pressures and temperatures.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Local atomic structure of K{sub x}Na{sub (1−x)}NbO{sub 3} by total x-ray diffraction

Local atomic structure of K{sub x}Na{sub (1−x)}NbO{sub 3} with 0.0 ≤ x ≤ 1.0 was studied using atomic Pair Distribution Function analysis based on x-ray diffraction. Powdered crystals were found to exhibit a re-entrant behavior by being orthorhombic (Amm2) for x < 0.42, monoclinic (Pm) for 0.42 ≤ x ≤ 0.63 and again orthorhombic (Amm2) for x > 0.63. Non-centrosymmetric structure of NaNbO{sub 3} (Amm2) was also evident in the piezoresponse force microscopy analysis revealing the presence of the ferroelectric domains and switching behavior. Lowering of the crystallographic symmetry for 0.42 ≤ x ≤ 0.63 is discussed in terms of differences in the sizes of Na{sup +} and K{sup +} ions and Na–O and K–O bond lengths. Besides being a bridging phase, as suggested by the previous studies on lead-based compositions, present study suggests that lower symmetry monoclinic phase of compositionally disordered perovskite solid solutions could also be a manifestation of the difference in the sizes of constituent ions and bond lengths.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Canted antiferromagnetism in the quasi-one-dimensional iron chalcogenide BaFe 2 Se 4

We report the synthesis and physical properties studies of quasi-one-dimensional (quais-1D) iron chalcogenide BaFe 2 Se 4 which shares the FeSe 4 tetrahedra building motif commonly seen in the iron chalcogenide superconductors. A high-quality polycrystalline sample was achieved by solid-state reaction method and characterized by x-ray diffraction, electrical resistivity, magnetic susceptibility, and neutron diffraction measurements. BaFe 2 Se 4 is a narrow gap semiconductor that magnetically orders at ~310 K. Therefore, both neutron powder diffraction results and isothermal M-H loops suggest a canted antiferromagnetic structure where Fe sublattices are antiferromagnetically ordered along the c-axis quasi-1D chain direction, resulting in a net ferromagnetic moment in the perpendicular direction along the a axis with tilted angle of 18.7° towards the b axis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Beamline K11 DIAD: a new instrument for dual imaging and diffraction at Diamond Light Source

The Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source is a new dual-beam instrument for full-field imaging/tomography and powder diffraction. This instrument provides the user community with the capability to dynamically image 2D and 3D complex structures and perform phase identification and/or strain mapping using micro-diffraction. The aim is to enable in situ and in operando experiments that require spatially correlated results from both techniques, by providing measurements from the same specimen location quasi-simultaneously. Using an unusual optical layout, DIAD has two independent beams originating from one source that operate in the medium energy range (7–38 keV) and are combined at one sample position. Here, either radiography or tomography can be performed using monochromatic or pink beam, with a 1.4 mm × 1.2 mm field of view and a feature resolution of 1.2 µm. Micro-diffraction is possible with a variable beam size between 13 µm × 4 µm and 50 µm × 50 µm. One key functionality of the beamline is image-guided diffraction, a setup in which the micro-diffraction beam can be scanned over the complete area of the imaging field-of-view. This moving beam setup enables the collection of location-specific information about the phase composition and/or strains at any given position within the image/tomography field of view. The dual beam design allows fast switching between imaging and diffraction mode without the need of complicated and time-consuming mode switches. Real-time selection of areas of interest for diffraction measurements as well as the simultaneous collection of both imaging and diffraction data of (irreversible) in situ and in operando experiments are possible.

36 MATERIALS SCIENCE↗