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DOE OSTI2018

Low-Frequency Phonon Driven Negative Thermal Expansion in Cubic GaFe(CN) 6 Prussian Blue Analogues

Here, the understanding of the negative thermal expansion (NTE) mechanism is vital not only for the development of new NTE compounds but also for effectively controlling thermal expansion. Here, we report an interesting isotropic NTE property in cubic GaFe(CN) 6 Prussian blue analogues (α l = –3.95 × 10 –6 K –1 , 100–475 K), which is a new example to understand the complex NTE mechanism. A combined study of synchrotron X-ray diffraction, X-ray total scattering, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations shows that the NTE of GaFe(CN)6 originates from the low-frequency phonons (< ~100 cm –1 ), which are directly related to the transverse vibrations of the atomic –Ga–N≡C–Fe– chains. Both the Ga–N and Fe–C chemical bonds are much softer to bend than to stretch. The direct evidence that transverse vibrational contribution to the NTE of GaFe(CN) 6 is dominated by N, instead of C atoms, is illustrated. It is interesting to find that the polyhedra of GaFe(CN) 6 are not rigid, which is a starting assumption in some models describing the NTE properties of other systems. The NTE mechanism can be vividly described by the “guitar-string” effect, which would be the common feature for the NTE property of many open-framework functional materials, such as Prussian blue analogues, oxides, cyanides, metal–organic frameworks, and zeolites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Magnetic structure of the mixed antiferromagnet NdMn 0.8 Fe 0.2 O 3

The magnetic structure of the mixed antiferromagnet NdMn 0.8 Fe 0.2 O 3 was resolved. Neutron powder diffraction data definitively resolve the Mn sublattice with a magnetic propagation vector k=(000) and with the magnetic structure (A x , F y , G z ) for 1.6 K N (≈ 59 K). The Nd sublattice has a (0, f y , 0) contribution in the same temperature interval. The Mn sublattice undergoes a spin-reorientation transition at T 1 ≈ 13 K while the Nd magnetic moment abruptly increases at this temperature. Powder x-ray diffraction shows a strong magnetoelastic effect at T N but no additional structural phase transitions from 3 to 300 K. Density functional theory calculations confirm the magnetic structure of the undoped NdMnO 3 as part of our analysis. Taken together, these results show that the magnetic structure of the Mn sublattice in NdMn 0.8 Fe 0.2 O 3 is a combination of the Mn and Fe parent compounds, but the magnetic ordering of the Nd sublattice spans a broader temperature interval than in the case of NdMnO 3 and NdFeO 3 . Lastly, this result is a consequence of the fact that the Nd ions do not order independently, but via polarization from the Mn/Fe sublattice.

36 MATERIALS SCIENCE↗

DOE OSTI2014

τ-MnAl with high coercivity and saturation magnetization

In this paper, high purity τ-Mn{sub 54}Al{sub 46} and Mn{sub 54−x}Al{sub 46}C{sub x}alloys were successfully prepared using conventional arc-melting, melt-spinning, and heat treatment process. The magnetic and the structural properties were examined using x-ray diffraction (XRD), powder neutron diffraction and magnetic measurements. A room temperature saturation magnetization of 650.5 kAm{sup -1}, coercivity of 0.5 T, and a maximum energy product of (BH){sub max} = 24.7 kJm{sup -3} were achieved for the pure Mn{sub 54}Al{sub 46} powders without carbon doping. The carbon substituted Mn{sub 54−x}Al{sub 46}C{sub x}, however, reveals a lower Curie temperature but similar saturation magnetization as compared to the carbon-free sample. The electronic structure of MnAl shows that the Mn atom possesses a magnetic moment of 2.454 μ{sub B} which results from strong hybridization between Mn-Al and Mn-Mn. We also investigated the volume and c/a ratio dependence of the magnetic moments of Mn and Al. The results indicate that an increase in the intra-atomic exchange splitting due to the cell volume expansion, leads to a large magnetic moment for the Mn atom. The Mn magnetic moment can reach a value of 2.9 μ{sub B} at a volume expansion rate of ΔV/V ≈ 20%.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Epitaxial Growth of Cadmium Selenide Films on Silicon with a Silicon Carbide Buffer Layer

An epitaxial cubic 350-nm-thick cadmium selenide has been grown on silicon for the first time by the method of evaporation and condensation in a quasi-closed volume. It is revealed that, in this method, the optimum substrate temperature is 590°C, the evaporator temperature is 660°C, and the growth time is 2 s. To avoid silicon etching by selenium with formation of amorphous SiSe{sub 2}, a high-quality ~100-nm-thick buffer silicon carbide layer has been synthesized on the silicon surface by substituting atoms. The powder diffraction pattern and the Raman spectrum unambiguously correspond to cubic cadmium selenide crystal. The ellipsometric, Raman, and electron diffraction analyses demonstrate high structural perfection of the cadmium selenide layer and the absence of a polycrystalline phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Earth Abundant High Temperature Materials for Radioisotope Power Conversion System

Advances in high temperature thermoelectric materials were made and published. Two major developments are out lined in this final report. Alkaline earth Zintl phases represent the starting point of a series of compounds selected for development due to their high abundance as the supply chain and as the availability of certain rare earths (i.e. Yb) are limited and can be difficult to obtain. A new Zintl phase, Ca 14 MnSb 11-x Sn x , where Sb is replaced by Sn resulting in changes to the band structure and properties. The structures are investigated by powder diffraction and samples consolidated into fully dense pellets for thermoelectric measurements. The band structure of a reasonable structure, Ca 14 MgSb 7 Sn 4 , is calculated in order to better understand the properties. These Sn containing phases show improved thermoelectric properties over Ca 14 MgSb 11 by increasing the Seebeck while decreasing resistivity without significant impact to the already low thermal conductivity. In addition, a composite phase of Yb 14 MgSb 11 was investigated. Composite phases have been shown to improve both the thermoelectric efficiency and mechanical properties of materials. Here we demonstrate an improved thermoelectric figure of merit, power factor, and mechanical properties for the high-temperature p-type Zintl phase Yb 14 MgSb 11 . Composites with 0, 1, 2, 3, 4, 6, 8 volume % 6 – 10 µm reduced Fe powder were prepared via a fast, scalable mechanical milling and spark plasma sintering procedure. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that Fe is not incorporated into the Yb 14 MgSb 11 structure. First order reversal curves and scanning electron microscopy images show that the Fe inclusions are larger and closer together with increasing Fe content. Thermogravimetric and differential scanning calorimetry show that the composites are stable up to 1273 K. The elastic constants of the 8 volume % Fe composite were measured by resonant ultrasound spectroscopy and show that Yb 14 MgSb 11 becomes stiffer with increasing Fe volume % and SEM after indentations show crack arresting occurs at the Fe interface. Thermoelectric properties on dense pellets are measured from 300 K – 1273 K. The thermoelectric power factor (PF= $\frac{S^2}{ρ}$) increases with increasing Fe content, with the 8 volume % Fe resulting in 40% higher PF than pristine Yb 14 MgSb 11 . The increase in PF is attributed to a systematic reduction in electrical resistivity. Peak thermoelectric figure of merit (zT= ($\frac{S^2T}{κρ}$) is observed at 3 volume % Fe, an 11% improvement in zT compared to Yb 14 MgSb 11 . Yb 14 MgSb 11 composites with Fe are compatible with Ce 0.9 Fe 3.5 Co 0.5 Sb 12 for thermoelectric generator couple segmentation.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2024

X-ray diffraction under grazing incidence conditions

Material properties frequently relate to structures at or near surfaces, particularly in thin films. As a result, it is essential to understand these structures at the molecular and atomistic levels. The most accurate and widely used techniques for characterizing crystallographic order are based on X-ray diffraction. When dealing with thin films or interfaces, standard approaches, such as single crystal or powder diffraction, are not suitable. However, X-ray diffraction under grazing incidence conditions can provide the required information. Here, in this Primer, grazing incidence X-ray diffraction (GIXD) is comprehensively introduced, starting from basic considerations on X-ray diffraction at crystals with reduced dimensionality and the optical properties of X-rays, followed by a more in-depth description of an experimental performance, including X-ray sources, goniometers and detectors. Experimental errors, limitations and reproducibility are discussed. Various applications, from highly ordered inorganic single crystal surfaces to weakly ordered polymer thin films, are presented to illustrate the potential of GIXD. Data visualizations, representations and evaluation strategies are summarized, based on the example of anthracene thin films. The Primer compiles information relevant to perform high-quality GIXD experiments, evaluate data and interpret results, to extend knowledge about X-ray diffraction from surfaces, interfaces and thin films.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Nucleation and growth of polar clusters with in-phase tilts into a long-range ferroelectric matrix in a sodium niobate based complex relaxor

In this study, we have investigated the temperature dependence of atomic ordering at multiple length scales in a lead-free sodium niobate-based relaxor, i.e., 0.75 NaNbO 3 -0.25 Ba 0.9⁢ Ca 0.1⁢ TiO 3 (NN-25BCT) via synchrotron x-ray diffraction, Raman spectroscopy, and pair distribution function analysis. High-resolution synchrotron x-ray powder diffraction (SXRD) measurements reveal a ferroelectric phase transition in the relaxor ferroelectric NN-25BCT below the Vogel-Fulcher freezing temperature (𝑇 VF ≈ 270 K). In addition, SXRD analysis demonstrates the competition between in-phase octahedral tilting and ferroelectric order at the long-range scale using mode crystallography. On the other hand, Raman spectroscopic analysis provides evidence of polar ordering for 𝑇 > 𝑇 VF (with tetragonal symmetry) persisting up to the Burns temperature (𝑇 B ). Furthermore, pair distribution function (PDF) analysis reveals the presence of a polar antiferrodistortive tetragonal phase with 𝑃⁢4⁢𝑏𝑚 space group at short ranges throughout the studied temperatures (i.e., 110 K ≤ 𝑇 ≤500 K), irrespective of nonpolar long-range ordering above 𝑇 VF . Therefore, our measurements provide direct evidence for the presence of polar ordering at short ranges and their gradual transformation into long-range polar ordering using an integrated multiscale structural analysis. In conclusion, as a result of a transition from relaxor to a ferroelectric phase in the vicinity of room temperature, NN-25BCT can be exploited for applications in pyroelectric detectors, electrocaloric devices, and multilayered ceramic capacitors.

36 MATERIALS SCIENCE↗

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 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 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↗