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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Assessment of the optimum degree of Sr{sub 3}Fe{sub 2}MoO{sub 9} electron-doping through oxygen removal: An X-ray powder diffraction and {sup 57}Fe Moessbauer spectroscopy study

We describe the preparation and structural characterization by X-ray powder diffraction (XRPD) and Moessbauer spectroscopy of three electron-doped perovskites Sr{sub 3}Fe{sub 2}MoO{sub 9-{delta}} with Fe/Mo = 2 obtained from Sr{sub 3}Fe{sub 2}MoO{sub 9}. The compounds were synthesized by topotactic reduction with H{sub 2}/N{sub 2} (5/95) at 600, 700 and 800 {sup o}C. Above 800 {sup o}C the Fe/Mo ratio changes from Fe/Mo = 2-1 < Fe/Mo < 2. The structural refinements of the XRPD data for the reduced perovskites were carried out by the Rietveld profile analysis method. The crystal structure of these phases is cubic, space group Fm3-bar m, with cationic disorder at the two different B sites that can be populated in variable proportions by the Fe atoms. The Moessbauer spectra allowed determining the evolution of the different species formed after the treatments at different temperatures and confirm that Fe ions in the samples reduced at 600, 700 and 800 {sup o}C are only in the high-spin Fe{sup 3+} electronic state.

36 MATERIALS SCIENCE↗
DOE OSTI2026

High-pressure neutron powder diffraction study of an arsenolite deuterium inclusion compound: structure and formation kinetics

High-pressure variable-temperature neutron powder diffraction was employed to investigate the synthesis and structural properties of arsenolite (As 4 O 6 ), a cubic arsenic( III ) oxide polymorph, and its inclusion compound with deuterium. The compound forms with the stoichiometry As 4 O 6 ·2D 2 , consistent with earlier findings. At 295 K and 1.96(2) GPa, D 2 molecules occupy the 16c site (0, 0, 0) and are aligned along the <111> direction. The diffraction data suggest that the D 2 molecules at this site become rotationally disordered upon decompression to 0.78(2) GPa at 120 K, while no occupancy is observed at the 8a position (⅛, ⅛, ⅛) under any of the studied conditions. The kinetic data of the high-pressure inclusion compound synthesis at 1.56(2) and 1.96(2) GPa were analyzed using the Avrami model. The Avrami exponent, 0.135(16), remains invariant with pressure, demonstrating that the reaction topochemistry is unaffected by compression. Similarly, the reaction rates, 0.29(3) and 0.23(3) min −0.135 at 1.56(2) and 1.96(2) GPa, respectively, exhibit negligible pressure dependence and suggest a surprisingly low activation volume of 1.6 cm 3 mol −1 for the reaction. These results provide detailed insight into the structural dynamics and kinetics of deuterium inclusion in arsenolite under high pressure.

Guńka, Piotr A. [Warsaw University of Technology (↗
DOE OSTI2025

Anthropogenic Influences on the Chemical and Mineral Composition in Pond Sediment by X-Ray Absorption Spectroscopy and X-Ray Powder Diffraction

Manmade detention ponds have historically been impacted by anthropogenic activities such as rainwater runoff, car emissions, and drainage from infrastructures, which can lead to complications for pond ecosystems. Sediment samples collected from the northern, southern, western, and eastern regions of a small pond on a suburban high school campus on Long Island, NY, were analyzed for potential chemical changes resulting from an inundation of water by a broken water main. Incorporating synchrotron X-ray techniques, sediment was analyzed using Submicron Resolution Spectroscopy, Tender Energy X-ray Spectroscopy, and X-ray Powder Diffraction to examine heavy metals, light elements, and minerals. Results include a Zn:Cu ratio increase from 4:1 to 10:1 in the eastern zone and a higher heavy metal presence in the western zone for all elements examined, with greater distribution throughout the pond post-inundation. Lighter elements appear to remain relatively unchanged. The appearance of diopside in the eastern zone post-inundation samples suggests contamination from the water main break, while the presence of carbonate minerals in the western zone is consistent with erosion of asphalt material from the adjacent parking lot.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond X-ray powder diffraction

The transient electronic and molecular structure arising from photoinduced charge transfer in transition metal complexes is studied by X-ray powder diffraction with a 100 fs temporal and atomic spatial resolution. Crystals containing a dense array of Fe(II)-tris(bipyridine) ([Fe(bpy){sub 3}]{sup 2+}) complexes and their PF{sub 6}{sup -} counterions display pronounced changes of electron density that occur within the first 100 fs after two-photon excitation of a small fraction of the [Fe(bpy){sub 3}]{sup 2+} complexes. Transient electron density maps derived from the diffraction data reveal a transfer of electronic charge from the Fe atoms and-so far unknown-from the PF{sub 6}{sup -} counterions to the bipyridine units. Such charge transfer (CT) is connected with changes of the inter-ionic and the Fe-bipyridine distances. An analysis of the electron density maps demonstrates the many-body character of charge transfer which affects approximately 30 complexes around a directly photoexcited one. The many-body behavior is governed by the long-range Coulomb forces in the ionic crystals and described by the concept of electronic polarons.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Using Complementary Methods of Synchrotron Radiation Powder Diffraction and Pair Distribution Function to Refine Crystal Structures with High Quality Parameters—A Review

Determination of the atomic-scale structures of certain fine-grained minerals using single-crystal X-ray diffraction (XRD) has been challenging because they commonly occur as submicron and nanocrystals in the geological environment. Synchrotron powder diffraction and scattering techniques are useful complementary methods for studying this type of minerals. In this review, we discussed three example studies investigated by combined methods of synchrotron radiation XRD and pair distribution function (PDF) techniques: (1) low-temperature cristobalite; (2) kaolinite; and (3) vernadite. Powder XRD is useful to determine the average structure including unit-cell parameters, fractional atomic coordinates, occupancies and isotropic atomic displacement parameters. X-ray/Neutron PDF methods are sensitive to study the local structure with anisotropic atomic displacement parameters (ADP). The results and case studies suggest that the crystal structure and high-quality ADP values can be obtained using the combined methods. The method can be useful to characterize crystals and minerals that are not suitable for single-crystal XRD.

58 GEOSCIENCES↗
DOE OSTI2018

Transmission in situ and operando high temperature X-ray powder diffraction in variable gaseous environments

In this paper, we describe a device for time-resolved synchrotron-based in situ and operando X-ray powder diffraction measurements at elevated temperatures under controllable gaseous environments. The respective gaseous sample environment is realized via a gas-tight capillary-in-capillary design, where the gas flow is achieved through an open-end 0.5 mm capillary located inside a 0.7 mm capillary filled with a sample powder. Thermal mass flow controllers provide appropriate gas flows and computer-controlled on-the-fly gas mixing capabilities. The capillary system is centered inside an infrared heated, proportional integral differential-controlled capillary furnace allowing access to temperatures up to 1000 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Neutron Powder Diffraction Study on the Magnetic Structure of NdPd 5 Al 2

The magnetic structure of NdPd 5 Al 2 has been studied by neutron powder diffraction. Here, we observed the magnetic reflections with the modulation vector q=(1/2,0,0)q=(1/2,0,0) below the ordering temperature T N . We also found a collinear magnetic structure with a Nd moment of 2.7(3) μB at 0.5 K parallel to the c-axis, where the ferromagnetically ordered a-planes stack with a four-Nd-layer period having a ++-- sequence along the a-direction with the distance between adjacent Nd layers equal to a/2 (magnetic space group P a nma). This “stripe”-like modulation is very similar to that in CePd 5 Al 2 with q=(0.235,0.235,0)q=(0.235,0.235,0) with the Ce moment parallel to the c-axis. These structures with in-plane modulation are a consequence of the two-dimensional nature of the Fermi surface topology in this family, originating from the unique crystal structure with a very long tetragonal unit cell and a large distance of >7 Å between the rare-earth layers separated by two Pd and one Al layers.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Early age hydration and pozzolanic reaction in natural zeolite blended cements: Reaction kinetics and products by in situ synchrotron X-ray powder diffraction

The in situ early-age hydration and pozzolanic reaction in cements blended with natural zeolites were investigated by time-resolved synchrotron X-ray powder diffraction with Rietveld quantitative phase analysis. Chabazite and Na-, K-, and Ca-exchanged clinoptilolite materials were mixed with Portland cement in a 3:7 weight ratio and hydrated in situ at 40 {sup o}C. The evolution of phase contents showed that the addition of natural zeolites accelerates the onset of C{sub 3}S hydration and precipitation of CH and AFt. Kinetic analysis of the consumption of C{sub 3}S indicates that the enveloping C-S-H layer is thinner and/or less dense in the presence of alkali-exchanged clinoptilolite pozzolans. The zeolite pozzolanic activity is interpreted to depend on the zeolite exchangeable cation content and on the crystallinity. The addition of natural zeolites alters the structural evolution of the C-S-H product. Longer silicate chains and a lower C/S ratio are deduced from the evolution of the C-S-H b-cell parameter.

36 MATERIALS SCIENCE↗
DOE OSTI2014

In-situ early-age hydration study of sulfobelite cements by synchrotron powder diffraction

Eco-friendly belite calcium sulfoaluminate (BCSA) cement hydration behavior is not yet well understood. Here, we report an in-situ synchrotron X-ray powder diffraction study for the first hours of hydration of BCSA cements. Rietveld quantitative phase analysis has been used to establish the degree of reaction (α). The hydration of a mixture of ye'elimite and gypsum revealed that ettringite formation (α ∼ 70% at 50 h) is limited by ye'elimite dissolution. Two laboratory-prepared BCSA cements were also studied: non-active-BCSA and active-BCSA cements, with β- and α′{sub H}-belite as main phases, respectively. Ye'elimite, in the non-active-BCSA system, dissolves at higher pace (α ∼ 25% at 1 h) than in the active-BCSA one (α ∼ 10% at 1 h), with differences in the crystallization of ettringite (α ∼ 30% and α ∼ 5%, respectively). This behavior has strongly affected subsequent belite and ferrite reactivities, yielding stratlingite and other layered phases in non-active-BCSA. The dissolution and crystallization processes are reported and discussed in detail. -- Highlights: •Belite calcium sulfoaluminate cements early hydration mechanism has been determined. •Belite hydration strongly depends on availability of aluminum hydroxide. •Orthorhombic ye’elimite dissolved at a higher pace than cubic one. •Ye’elimite larger reaction degree yields stratlingite formation by belite reaction. •Rietveld method quantified gypsum, anhydrite and bassanite dissolution rates.

36 MATERIALS SCIENCE↗
DOE OSTI2015

CaCO 3 Crystallite Evolution during CaO Carbonation: Critical Crystallite Size and Rate Constant Measurement by In-Situ Synchrotron Radiation X-ray Powder Diffraction

In this work, the evolution of the CaCO 3 crystalline phase during the CaO–CO 2 reaction was investigated by means of in situ synchrotron radiation X-ray powder diffraction performed at the Advanced Photon Source (APS) facilities of the Argonne National Laboratory. CO 2 absorption experiments were carried out in a high temperature reaction capillary with a controlled atmosphere of pure carbon dioxide (CO 2 partial pressure of 1 bar) and in the temperature range between 450 and 750 °C, using CaO-based sorbents obtained by calcination of commercial calcium carbonate. The Rietveld refinement method was applied to estimate the average size of the CaCO 3 crystallites formed during a carbonation time of 20 min, as a function of the carbonation temperature and of the initial calcination conditions. Local maxima were observed in the CaCO 3 crystallite size versus time curves and were identified as the critical CaCO 3 crystallite sizes, marking the transition between the first fast carbonation stage and the second reaction stage controlled by product-layer diffusion. A relationship between this parameter and the reaction temperature, as well as with the initial (at the beginning of carbonation) CaO crystallite size, were found. The CaCO 3 critical crystallite sizes were used to estimate the active surface areas of the CaO sorbent particles where CaCO 3 crystals form and grow. Here, the computed active surface areas were utilized to calculate the kinetic parameters of the surface carbonation reaction: a reaction rate constant of 4.41 × 10 –4 mol/m 2 s, with zero-activation energy, was obtained.

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

Crystal structure of pentasodium hydrogen dicitrate from synchrotron X-ray powder diffraction data and DFT comparison

The crystal structure of pentasodium hydrogen dicitrate, Na 5 H(C 6 H 5 O 7 ) 2 , has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Each of the two independent citrate anions is joined into a dimer by very strong centrosymmetric O—H...O hydrogen bonds, with O...O distances of 2.419 and 2.409 Å. Four octahedrally coordinated Na + ions share edges to form open layers parallel to the ab plane. A fifth Na + ion in trigonal–bipyramidal coordination shares faces with NaO 6 octahedra on both sides of these layers.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Powder diffraction by fixed incident angle reflection using a curved position-sensitive detector

As curved position-sensitive detectors improve in angular resolution, the effects that fixed incident angle reflection have on X-ray diffraction peaks become more apparent. In this study the effects of sample transparency, incident beam height, detector resolution and sample displacement on the intensity, location, width and shape of powder diffraction peaks were examined. The functions describing each of these phenomena are presented and were successfully used to quantitatively model the diffraction peaks collected in this geometry. Three distinct regimes of diffraction peak resolution were identified from the phenomena that limit the peak variance. Pertinent criteria based on experimental parameters have been outlined to classify fixed incident angle reflection experiments into each regime. Guidelines for improvement of experimental resolution and for conducting analysis of data acquired using fixed incident angle reflection geometry and curved position-sensitive detectors are also provided.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Structure resolution of Ba{sub 5}Al{sub 3}F{sub 19} and Iivestigation of fluorine ion dynamics by synchrotron powder diffraction, variable-temperature solid-state NMR, and quantum computations.

The room temperature structure of Ba{sub 5}Al{sub 3}F{sub 19} has been solved using electron microscopy and synchrotron powder diffraction data. One-dimensional (1D) {sup 27}Al and ultrafast magic-angle-spinning (MAS) {sup 19}F NMR spectra have been recorded and are in agreement with the proposed structural model for Ba{sub 5}Al{sub 3}F{sub 19}. The {sup 19}F isotropic chemical shift and {sup 27}Al quadrupolar parameters have been calculated using the CASTEP code from the experimental and density functional theory geometry-optimized structures. After optimization, the calculated NMR parameters of both the {sup 19}F and {sup 27}Al nuclei show improved consistency with the experimental values, demonstrating that the geometry optimization step is necessary to obtain more accurate and reliable structural data. This also enables a complete and unambiguous assignment of the {sup 19}F MAS NMR spectrum of Ba{sub 5}Al{sub 3}F{sub 19}. Variable-temperature 1D MAS {sup 19}F NMR experiments have been carried out, showing the occurrence of fluorine ion mobility. Complementary insights were obtained from both two-dimensional (2D) exchange and 2D double-quantum dipolar recoupling NMR experiments, and a detailed analysis of the anionic motion in Ba{sub 5}Al{sub 3}F{sub 19} is proposed, including the distinction between reorientational processes and chemical exchange involving bond breaking and re-formation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

In situ synchrotron powder diffraction study of the setting reaction kinetics of magnesium-potassium phosphate cements

This work reports a kinetic study of the formation of magnesium-potassium phosphate cements accomplished using in-situ synchrotron powder diffraction. The reaction: MgO + KH{sub 2}PO{sub 4} + 5H{sub 2}O → MgKPO{sub 4} · 6H{sub 2}O was followed in situ in the attempt of contributing to explain the overall mechanism and assess the influence of periclase (MgO) grain size and calcination temperature (1400-1600 °C) on the reaction kinetics. Numerical kinetic parameters for the setting reaction have been provided for the first time. The best fit to the kinetic data was obtained using a weighted nonlinear model fitting method with two kinetic equations, representing two consecutive, partially overlapping processes. MgO decomposition could be described by a first order (F1) model followed by a Jander diffusion (D3) controlled model. Crystallization of the product of reaction was modelled using an Avrami model (A{sub n}) followed by a first order (F1) chemical reaction. A reaction mechanism accounting for such results has been proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Anti-site mixing and magnetic properties of Fe 3 Co 3 Nb 2 studied via neutron powder diffraction

Here, we studied the crystal structure and magnetic properties of the rare-earth-free intermetallic compound Fe 3 Co 3 Nb 2 , which has recently been demonstrated to have potentially high magnetic anisotropy, using temperature-dependent neutron powder diffraction. Furthermore, the temperature dependence of the diffraction spectra reveals a magnetic transition between 300 and 400 K, in agreement with the magnetometry measurements. According to the structural refinement of the paramagnetic state and the substantial magnetic contribution to the diffuse scattering in the ferromagnetic state, the Fe/Co anti-site mixing is so strong that the site occupation for Fe and Co is almost random. The projection of the magnetic moments turned out to be non-zero along the c axis and in the a–b plane of Fe 3 Co 3 Nb 2 , most likely because of the exchange interactions between the randomly orientated nanograins in the samples. These findings suggest that future studies on the magnetism of Fe 3 Co 3 Nb 2 need to take the Fe/Co anti-site mixing into account, and the exchange interactions need to be suppressed to obtain large remanence and coercivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Crystal Structure of (Lu{sub 1−x}Ca{sub x})Ba{sub 2}Cu{sub 3}O{sub 7−z} (x = 0, 0.2) Superconducting Compounds Studied by Neutron Powder Diffraction

The crystalline structures of two polycrystalline samples of (Lu{sub 1−x}Ca{sub x})Ba{sub 2}Cu{sub 3}O{sub 7−z} with x = 0 (pure sample) and x = 0.2 (Ca-doped sample) have been analyzed by using neutron powder diffraction techniques to address the structural mechanisms associated with changes in superconducting behavior induced by Ca doping. The pure and Ca-doped samples exhibit superconductivity around 87 and 32 K, respectively. The room-temperature thermoelectric power measurements indicate that both the x = 0 and 0.2 samples are in overdoped state. The Rietveld refinements of the neutron diffraction data collected at room temperature for the pure and Ca-doped samples show that the higher level of oxygen vacancies is located on both the CuO{sub 2} planes and the apical oxygen sites for the pure sample compared to those of the Ca-doped sample. The present results suggest that the decrease in T{sub c} observed in the Ca-doped sample is mainly caused by the hole overdoping effect rather than by oxygen vacancies in the CuO{sub 2} planes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Magnetic ground state of the two isostructual polymeric quantum magnets [ Cu ( HF 2 ) ( pyrazine ) 2 ] SbF 6 and [ Co ( HF 2 ) ( pyrazine ) 2 ] SbF 6 investigated with neutron powder diffraction

The magnetic ground state of two isostructural coordination polymers, (i) the quasi-two-dimensional S=1/2 square-lattice antiferromagnet [Cu(HF 2 )(pyrazine) 2 ]SbF 6 and (ii) a related compound [Co(HF 2 )(pyrazine)2]SbF6, was examined with neutron powder diffraction measurements. We find that the ordered moments of the Heisenberg S=1/2 Cu(II) ions in [Cu(HF 2 )(pyrazine) 2 ]SbF 6 are 0.6(1)μ b , while the ordered moments for the Co(II) ions in [Co(HF 2 )(pyrazine) 2 ]SbF 6 are 3.02(6)μ b . For Cu(II), this reduced moment indicates the presence of quantum fluctuations below the ordering temperature. We also show from heat capacity and electron spin resonance measurements that due to the crystal electric field splitting of the S=3/2 Co(II) ions in [Co(HF 2 )(pyrazine) 2 ]SbF 6 , this isostructual polymer also behaves as an effective spin-half magnet at low temperatures. Furthermore, the Co moments in [Co(HF 2 )(pyrazine) 2 ]SbF 6 show strong easy-axis anisotropy, neutron diffraction data, which do not support the presence of quantum fluctuations in the ground state, and heat capacity data, which are consistent with 2D or close to 3D spatial exchange anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗