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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Study of Antisite Defects in Hydrothermally Prepared LiFePO4 by in Situ X-ray Diffraction

Hydrothermal synthesis has proven to be a cost-effective, energy-efficient approach for the manufacture of lithium iron phosphate (LiFePO{sub 4}) and its related materials. However, hydrothermally prepared LiFePO{sub 4} typically suffers from antisite defects, where some of the iron resides on lithium sites and restricts lithium-ion mobility. A post-heat-treatment temperature of around 700 C is generally used to eliminate cation disorder, but little is known about these antisite defects or their concentration as a function of the post-heat-treatment temperature. In this study, time-resolved, synchrotron X-ray diffraction reveals that antisite defects are completely eliminated above 500 C, suggesting that the electrochemical performance may be significantly enhanced by a milder postsynthesis heat treatment. The preliminary electrochemical results show a significant enhancement in the electrochemical capacity with the defect-free material, with the specific capacity increasing by approximately 60% at a C/20 rate.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Novel Protein Crystal Growth Electrochemical Cell For Applications in X-ray Diffraction and Atomic Force Microscopy

A new crystal growth cell based on transparent indium tin oxide (ITO) glass-electrodes for electrochemically assisted protein crystallization allows for reduced nucleation and crystal quality enhancement. The crystallization behavior of lysozyme and ferritin was monitored as a function of the electric current applied to the growth cell. The X-ray diffraction analysis showed that for specific currents, the crystal quality is substantially improved. No conformational changes were observed in the 3D crystallographic structures determined for crystals grown under different electric current regimes. Finally, the strong crystal adhesion on the surface of ITO electrode because of the electroadhesion allows a sufficiently strong fixing of the protein crystals, to undergo atomic force microscopy investigations in a fluid cell.

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

In Situ X-Ray Diffraction Study of Na+ Saturated Montmorillonite Exposed to Variably Wet Super Critical CO2

Reactions involving variably hydrated super critical CO{sub 2} (scCO{sub 2}) and a Na saturated dioctahedral smectite (Na-STX-1) were examined by in situ high-pressure x-ray diffraction at 50 C and two different pressures (90 and 180 bars); conditions that are relevant to long term geologic storage of CO{sub 2}. Both hydration and dehydration reactions were rapid with appreciable reaction occurring in minutes and near steady state within an hour. Hydration occurred stepwise as a function of increasing H{sub 2}O in the system; 1W, 2W-3W, and >3W clay hydration states were stable from {approx} 1.5-30%, {approx} 31-55 < 64%, and {ge} {approx} 71% H{sub 2}O saturation in scCO{sub 2}, respectively. Exposure of sub 1W clay to anhydrous scCO{sub 2} caused interlayer expansion, not contraction as expected for dehydration. In contrast, control experiments using pressurized N{sub 2} and similar initial conditions as in the scCO{sub 2} study, showed little to no change in the d{sub 001} spacing, or hydration states, of the clay. Comparison of the N{sub 2} and scCO{sub 2} experiments indicates that the induced changes are not a pressure effect, but rather are due to the intrinsic properties of scCO{sub 2}. A salient implication for CO{sub 2} sequestration and cap rock integrity is that clays can dehydrate when exposed to wet scCO{sub 2}. For example, the {approx} 3W clay hydration state appears to be unstable and the structure will collapse by {approx} 3 {angstrom} in the c* direction, or {approx} 15%, if exposed to scCO{sub 2} at less than or equal to about 64% H{sub 2}O saturation. Further, the evidence suggests that CO{sub 2} intercalated the interlayer region of the sub 1W clay which might provide a secondary trapping mechanism for CO{sub 2}.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Neutron diffraction studies of a four-coordinated hydride in near square-planar geometry

The structure of a nanospheric polyhydrido copper cluster, [Cu 20 (H) 11 {S 2 P(O i Pr) 2 } 9 ], was determined by single-crystal neutron diffraction. Cu 20 cluster consists of an elongated triangular orthobicupola constructed from 18 Cu atoms that encapsulate a [Cu 2 H 5 } 3- ion in the center with an exceptionally short Cu-Cu distance. The eleven hydrides in the cluster display three different coordination modes to the Cu atoms: Six μ 3 -hydrides in pyramidal geometry, two μ 4 -hydrides in tetrahedral cavity, and three μ 4 -hydrides in an unprecedented near square-planar geometry. The neutron data set was collected on a small crystal of the size 0.20 mm x 0.50 mm x 0.65 mm for seven days using the Spallation Neutron Source TOPAZ single-crystal time-of-flight Laue diffractometer at the Oak Ridge National Laboratory. Furthermore, the final R-factor is 8.64% for 16014 reflections.

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

Understanding Metal Directed-Assembly Growth of Single-Crystal Organic Nanowires: Time-Resolved, In-Situ X-Ray Diffraction and First-Principles Theoretical Study

The deterministic growth of oriented crystalline organic nanowires (CONs) from the vapor-solid chemical reaction (VSCR) between small-molecule reactants and metal nanoparticles has been demonstrated in several studies to date, however the growth mechanism has not yet been conclusively understood. Here, the VSCR growth of M-TCNQF4 (where M is Cu- or Ag-) nanowires is investigated both experimentally and theoretically with time-resolved, in-situ x-ray diffraction (XRD) and first-principles atomistic calculations, respectively, to understand how metals (M) direct the assembly of small molecules into CONs, and what determines the selectivity of a metal for an organic vapor reactant in the growth process. Analysis of the real-time growth kinetics data using a modified Avrami model indicates that the formation of CONs from VSCR follows a one-dimensional ion diffusion-controlled tip growth mechanism wherein metal ions diffuse from a metal film through the nanowire to its tip where they react with small molecules to continue growth. The experimental data and theoretical calculations indicate that the selectivity of different metals to induce nanowire growth depends strongly upon effective charge transfer between the organic molecules and the metal. Specifically, the experimental finding that Cu ions can exchange and replace Ag ions in Ag-TCNQF4 to form Cu-TCNQF4 nanowires is explained by the significantly stronger chemical bond between Cu and TCNQF4 molecules than for Ag, due to the strong spin-dependent electronic contribution of Cu. Understanding how to control the VSCR growth process may enable the synthesis of novel organic nanowires with axial or coaxial p/n junctions for organic nanoelectronics and solar energy harvesting.

14 SOLAR ENERGY↗
DOE OSTI2021

Operando X-ray Diffraction Studies of the Mg-Ion Migration Mechanisms in Spinel Cathodes for Rechargeable Mg-Ion Batteries

A promising high-voltage spinel oxide cathode material MgCrMnO 4 with 18% Mg/Mn inversion was synthesized successfully. A new custom operando battery device was designed to study the cation migration mechanisms of the MgCrMnO 4 cathode using 0.1 M Mg(TPFA) 2 electrolyte dissolved in triglyme and activated carbon as the anode. For the first time in multivalent batteries, high-quality operando diffraction data enabled the accurate quantification of cation contents in the host structure. Besides the exceptional reversibility of 12% Mg 2+ insertion in Mg 1- x CrMnO 4 ( x ≤ 1), a partially reversible insertion of excess Mg 2+ during overdischarging was also observed. Moreover, the insertion/extraction reaction was experimentally shown to be accompanied by a series of cation redistributions in the spinel framework, which were further supported by density functional theory calculations. Furthermore, the inverted Mn is believed to be directly involved in the cation migrations, which would cause voltage hysteresis and irreversible structural evolution after overdischarging. Tuning the Mg/Mn inversion rate could provide a direct path to further optimize spinel oxide cathodes for Mg-ion batteries, and more generally, the operando techniques developed in this work should play a key role in understanding the complex mechanisms involved in multivalent ion insertion systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Visualizing Light-Induced Microstrain and Phase Transition in Lead-Free Perovskites Using Time-Resolved X-Ray Diffraction

Metal halide perovskites have emerged as promising materials for optoelectronic applications in the last decade. A large amount of effort has been made to investigate the interplay between the crystalline lattice and photoexcited charge carriers as it is vital to their optoelectronic performance. Among them, ultrafast laser spectroscopy has been intensively utilized to explore the charge carrier dynamics of perovskites, from which the local structural information can only be extracted indirectly. Here, we have applied a time-resolved X-ray diffraction technique to investigate the structural dynamics of prototypical two-dimensional lead-free halide perovskite Cs 3 Bi 2 Br 9 nanoparticles across temporal scales from 80 ps to microseconds. We observed a quick recoverable (a few ns) photoinduced microstrain up to 0.15% and a long existing lattice expansion (~a few hundred nanoseconds) at mild laser fluence. Once the laser flux exceeds 1.4 mJ/cm 2 , the microstrain saturates and the crystalline phase partially transfers into a disordered phase. This photoinduced transient structural change can recover within the nanosecond time scale. Furthermore, these results indicate that photoexcitation of charge carriers couples with lattice distortion, which fundamentally affects the dielectric environment and charge carrier transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Redox-Induced Microstructure and Phase Dynamics in Nickel: Insights from In Situ Synchrotron X-ray Diffraction

Using in situ synchrotron X-ray diffraction, we interrogate the microstructural and phase evolution of polycrystalline nickel (Ni) during redox cycling in O 2 , H 2 , and H 2 O environments. Oxidation in O 2 promotes strong (111) texturing in both the NiO overlayer and the underlying Ni substrate. However, this crystallographic alignment is lost following reduction in H 2 and subsequent reoxidation, demonstrating irreversible microstructural changes. H 2 exposure leads to proton dissolution into the Ni lattice, triggering a localized phase transition from face-centered cubic (FCC) to hexagonal close-packed (HCP) Ni in hydrogen-saturated regions. In H 2 O-containing atmospheres, dissociative H 2 O adsorption produces protons that permeate the NiO layer, forming γ-NiOOH within the NiO lattice and HCP Ni beneath the NiO overlayer as protons accumulate. Kinetic analysis via the Johnson-Mehl-Avrami–Kolmogorov model uncovers distinct growth mechanisms: preoxidized Ni surfaces follow one-dimensional (1D) kinetics for NiO, γ-NiOOH, and HCP growth, whereas pristine Ni exhibits three-dimensional (3D) kinetics due to island-like nucleation and growth of NiO. Furthermore, these results highlight the critical interplay between H 2 O dissociation, hydrogen permeation, and redox-driven phase transformations, with practical implications in engineering nickel-based catalysts and hydrogen storage systems through controlled microstructural and phase evolution.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Rotator Phases of n-Heptane under High Pressure: Raman Scattering and X-ray Diffraction Studies

We performed high-pressure Raman scattering and angle-dispersive synchrotron X-ray diffraction measurements on n-heptane at room temperature. It has been found that n-heptane undergoes a liquid to rotator phase III (R{sub III}) transition at 1.2 GPa and then transforms into another rotator phase R{sub IV} at about 3 GPa. As the pressure reaches 7.5 GPa, a transition from an orientationally disordered R{sub IV} phase to an ordered crystalline state starts and is completed around 14.5 GPa. Our results clearly present the high-pressure phase transition sequence (liquid-R{sub III}-R{sub IV}-crystal) of n-heptane, similar to that of normal alkanes.

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

Kinetics of Methane Hydrate Decomposition Studied via in Situ Low Temperature X-ray Powder Diffraction

Gas hydrates are known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice termed self-preservation or anomalous preservation. As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Two regions of slowed decomposition for methane hydrate, 180 200 K and 230 260 K, were observed, and the kinetics were studied by in situ low temperature x-ray powder diffraction. The kinetic constants for ice formation from methane hydrate were determined by the Avrami model within each region and activation energies, Ea, were determined by the Arrhenius plot. Ea determined from the data for 180 200 K was 42 kJ/mol and for 230 260 K was 22 kJ/mol. The higher Ea in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions.

anomalous preservation↗
DOE OSTI2012

Structure of Hydrated Poly(d,l-lactic acid) Studied with X-ray Diffraction and Molecular Simulation Methods

The effect of hydration on the molecular structure of amorphous poly(D,L-lactic acid) (PDLLA) with 50:50 L-to-D ratio has been studied by combining experiments with molecular simulations. X-ray diffraction measurements revealed significant changes upon hydration in the structure functions of the copolymer. Large changes in the structure functions at 10 days of incubation coincided with the large increase in the water uptake from {approx} 1 to {approx} 40% and the formation of voids in the film. Computer modeling based on the recently developed TIGER2/TIGER3 mixed sampling scheme was used to interpret these changes by efficiently equilibrating both dry and hydrated models of PDLLA. Realistic models of bulk amorphous PDLLA structure were generated as demonstrated by close agreement between the calculated and the experimental structure functions. These molecular simulations were used to identify the interactions between water and the polymer at the atomic level including the change of positional order between atoms in the polymer due to hydration. Changes in the partial O-O structure functions, about 95% of which were due to water-polymer interactions, were apparent in the radial distribution functions. These changes, and somewhat smaller changes in the C-C and C-O partial structure functions, clearly demonstrated the ability of the model to capture the hydrogen-bonding interactions between water and the polymer, with the probability of water forming hydrogen bonds with the carbonyl oxygen of the ester group being about 4 times higher than with its ether oxygen.

08 HYDROGEN↗
DOE OSTI2019

Fast and interpretable classification of small X-ray diffraction datasets using data augmentation and deep neural networks

X-ray diffraction (XRD) data acquisition and analysis is among the most time-consuming steps in the development cycle of novel thin-film materials. We propose a machine-learning-enabled approach to predict crystallographic dimensionality and space group from a limited number of thin-film XRD patterns. We overcome the scarce-data problem intrinsic to novel materials development by coupling a supervised machine learning approach with a model-agnostic, physics-informed data augmentation strategy using simulated data from the Inorganic Crystal Structure Database (ICSD) and experimental data. As a test case, 115 thin-film metal-halides spanning 3 dimensionalities and 7 space-groups are synthesized and classified. After testing various algorithms, we develop and implement an all convolutional neural network, with cross-validated accuracies for dimensionality and space-group classification of 93% and 89%, respectively. We propose average class activation maps, computed from a global average pooling layer, to allow high model interpretability by human experimentalists, elucidating the root-causes of misclassification. Finally, we systematically evaluate the maximum XRD pattern step size (data acquisition rate) before loss of predictive accuracy occurs, and determine it to be 0.16° 2θ, which enables an XRD pattern to be obtained and classified in 5.5 minutes or less.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Dehydration kinetics of nanoconfined water in beryl probed by high temperature single crystal synchrotron X-ray diffraction

Understanding changes in material properties through external stimuli plays a key role in validating the expected performance of materials and engineering material properties in a controlled manner. Here, we introduce a fundamental protocol to deduce dehydration reactions kinetics of water confined in nanopore channels, with the cyclosilicate beryl as the scaffold of interest, using time-resolved synchrotron X-ray diffraction (SXRD), in the temperature interval of 298–1038 K. The temperature-dependent intensity (I) of the strongest reflection (112) was used as the crystallite variable. An estimation of an isobaric thermal crystallite coefficient, k, analogous with the isobaric thermal expansion coefficient, established the rate of relative crystallization as a function of temperature, $\frac{∂I}{∂T}$. A plot of lnk and $\frac{1}{T}$ gives rise to two kinetic steps, indicating a slow dehydration stage up to ~ 700 K and a fast dehydration stage up to the investigated temperature 1038 K. The crystal structure of beryl determined up to 1038 K, in temperature increment as small as 10 K, indicates the presence of channel ions Na and Fe and a gradual decrease of water upon heating.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

X-ray diffraction of metastable structures from supercooled liquid hydrogen

We report time resolved observations of the crystallization from liquid hydrogen, supercooled to temperatures below the melting point, using 11.2 keV X-ray diffraction from the Linac Coherent Light Source (LCLS). Changes to the metastable solid and liquid structure factors have been dynamically measured. This allows for a direct determination of the lowest energy crystal polymorphs, the stacking probabilities, as well as the liquid and solid densities and temperatures. Such measurements provide experimental evidence of an Arrhenius-like growth kinetics along the stacking direction during supercooling.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A photo-induced excited state structure of a hetero-bimetallic ionic pair complex, Nd(DMA)[subscript 4](H[subscript 2]O)[subscript 4]Fe(CN)[subscript 6]·3H[subscript 2]O, analyzed by single crystal X-ray diffraction

The excited state crystal structure of the ionic complex Nd(DMA){sub 4}(H{sub 2}O){sub 4}-Fe(CN){sub 6} {center_dot} 3H{sub 2}O (DMA = dimethylacetamide) has been determined at 15 K upon UV illumination by single crystal X-ray diffraction. Significant structural changes are observed around the Fe site in the excited state. These changes are similar to those observed for a related molecular compound exhibiting photomagnetic properties.

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

Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction

We report the spin state photo-switching dynamics in two polymorphs of a spin-crossover molecular complex triggered by a femtosecond laser flash, as determined by combining femtosecond optical pump-probe spectroscopy and picosecond X-ray diffraction techniques. The light-driven transformations in the two polymorphs are compared. Combining both techniques and tracking how the X-ray data correlate with optical signals allow understanding of how electronic and structural degrees of freedom couple and play their role when the switchable molecules interact in the active crystalline medium. The study sheds light on crossing the border between femtochemistry at the molecular scale and femtoswitching at the material scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

In situ analysis of the nucleation of O- and Zn-polar ZnO nanowires using synchrotron-based X-ray diffraction

The selection of the polarity of ZnO nanowires grown by chemical bath deposition offers a great advantage for their integration into a wide variety of engineering devices. However, the nucleation process of ZnO nanowires and its dependence on their polarity is still unknown despite its importance for optimizing their morphology and properties and thus to enhance the related device performances. To tackle this major issue, we combine an in situ analysis of the nucleation process of O- and Zn-polar ZnO nanowires on O- and Zn-polar ZnO single crystals, respectively, using synchrotron radiation-based grazing incidence X-ray diffraction with ex situ transmission and scanning electron microscopy. We show that the formation of ZnO nanowires obeys three successive phases from the induction, through nucleation to growth phases. Additionally, the characteristics of each phase, including the nucleation temperature, the shape and dimension of nuclei, as well as their radial and axial development are found to depend on the polarity of ZnO nanowires. A comprehensive description reporting the dominant physicochemical processes in each phase and their dependence on the polarity of ZnO nanowires is presented, revisiting their formation process step-by-step. These findings provide a deeper understanding of the phenomena at work during the growth of ZnO nanowires by chemical bath deposition and open the perspective to develop a more accurate control of their properties at each step of the formation process.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Photo-induced structural dynamics of o -nitrophenol by ultrafast electron diffraction

The photo-induced dynamics of o-nitrophenol, particularly its photolysis, has garnered significant scientific interest as a potential source of nitrous acid in the atmosphere. Although the photolysis products and preceding photo-induced electronic structure dynamics have been investigated extensively, the nuclear dynamics accompanying the non-radiative relaxation of o-nitrophenol on the ultrafast timescale, which include an intramolecular proton transfer step, have not been experimentally resolved. Herein, we present a direct observation of the ultrafast nuclear motions mediating photo-relaxation using ultrafast electron diffraction. Here, this work spatiotemporally resolves the loss of planarity which enables access to a conical intersection between the first excited state and the ground state after the proton transfer step, on the femtosecond timescale and with sub-Angstrom resolution. Our observations, supported by ab initio multiple spawning simulations, provide new insights into the proton transfer mediated relaxation mechanism in o-nitrophenol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗