Search NASA⌕ Search

SEARCH · Search NASA

Results for “extended X-ray absorption fine structure”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Magnetic field induced modification of a first-order ferromagnetic transition in Eu 2 ⁢In

Here, we present a comprehensive study of the temperature-and magnetic-field-dependent magnetization, specific heat, and local crystal structure across the first-order ferromagnetic–paramagnetic transition in Eu 2 ⁢In. Anomalies in the magnetocaloric response are observed near 𝐻 ≈ 25 kOe, including changes in field scaling of magnetic entropy, local entropy exponent, and universal master curve, which suggest an apparent weakening of the first-order character of the transition. However, quantitative analysis of the magnetocaloric parameters together with modified Arrott plots demonstrates that the transition remains first order up to at least 70 kOe. Specific-heat measurements reveal a field-induced splitting of the sharp zero-field anomaly into a doublet, providing a natural explanation for the change in the magnetocaloric response. Magnetic-field-dependent extended x-ray absorption fine structure (EXAFS) measurements show no detectable field-induced changes in the local coordination environment of Eu. We therefore attribute these observations to a magnetic-field-induced two-step transition process in Eu 2 ⁢In.

Kumar, Ajay [Ames Laboratory (AMES), Ames, IA (Uni↗
DOE OSTI2025

Mechanistic Insights into Adsorptive and Catalytic Reactions from Controllable Distributions of Metal Cations (Pd, Pt, Ni, Cr, Cu) as [M‐OH] +1 /1Al or M +2 /2Al in Zeolites

Anchoring divalent metal ions in the same zeolite framework with similar Si/Al ratio selectively as zeolite-bound M +2 or [M +2 -OH] +1 cationic species enables critical comparison of the species’ intrinsic reactivity for industrially and fundamentally relevant reactions. H-BEA zeolites with similar Si/Al ratios but differing framework Al siting were used to anchored multiple divalent metal cations (Ni, Pd, Pt, Cr, Cu) in the zeolite micropores. State-of-the-art infrared (IR) spectroscopy, electron paramagnetic resonance (EPR) measurements, including two-dimensional pulsed HYSCORE EPR, extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT) calculations together provide unambiguous evidence for the selective formation of divalent metal cations as M +2 /2Al species (for H-BEA prepared in the conventional hydroxide media), and [M +2 OH] +1 /1Al species for H-BEA prepared in HF. Solid-state proton-decoupled triple-quantum magic-angle spinning (3Q MAS) NMR measurements confirmed contrasting Al distributions in the two H-BEA zeolites, which led to a contrasting divalent cation speciation. The reactivities of the two cationic species were explored for catalytic and adsorptive applications in both organometallic homogeneous and heterogeneous catalysis. This work demonstrates their divergent reactivity in ethylene dimerization, ethylene oxidation (Wacker process), selective catalytic reduction (SCR) of NO, NO adsorption, and methane oxidation. Both M +2 /2Al and [M +2 OH] +1 /1Al cations are both active for ethylene dimerization, but [M +2 OH] +1 /1Al species show higher reaction rates for each Pd, Ni, Pt. [M +2 OH] +1 /1Al is active for acetaldehyde formation in Wacker ethylene oxidation. A new active site for ethylene oligomerization is proposed that possesses a terminal OH group (Cr-OH) in Phillips catalysts evident by a nearly inactive isolated Cr +2 /2Al species that contrast an active Cr─OH motif.

Divalent metal cations in a zeolite↗
DOE OSTI2025

Molecular insights into Yb(III) speciation in sulfate-bearing hydrothermal fluids from X-ray absorption spectra informed by ab initio molecular dynamics

Rare earth elements (REEs) are critical for advanced technologies, yet in hydrothermal aqueous solutions the molecular level details of their interaction with ligands that control their geochemical transport and deposition remain poorly understood. Here, this study elucidates the coordination behavior of Yb 3+ in sulfate-rich hydrothermal fluids using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulations. By integrating multi-angle EXAFS with AIMD-derived constraints, we precisely resolve Yb 3+ coordination structures and ligand interactions under hydrothermal conditions. At room temperature, Yb 3+ is coordinated by five water molecules and two sulfate ligands (coordination number, CN = 8), forming a distorted square antiprism geometry. Increasing temperature induces progressive dehydration, reducing the hydration shell and favoring stronger sulfate complexation. At 200°C, sulfate ligands reorganize around Yb 3+ , shifting its geometry to a capped octahedron (CN = 7). At 300 °C, sulfate binding dominates, leading to structural reorganization that parallels the onset of sulfate mineral precipitation, consistent with the retrograde solubility of REE sulfates. These findings provide direct molecular-scale evidence that sulfate acts as both a transport and deposition ligand, critically influencing REE mobility in geochemical environments. Our results can also help to refine thermodynamic models of REE speciation in high-temperature hydrothermal fluids and improve our understanding of REE ore formation processes in nature.

AIMD↗
DOE OSTI2026

Robust Automatic EXAFS First-Shell Fits

Extended X-ray absorption fine structure (EXAFS) is a widely used technique for atomic structure determination. Fourier transformation connects EXAFS in k space and R space. However, determining the appropriate k-range for the transformation can be challenging, but critical for the first-shell fit. In this study, we present an automatic method to determine the k-range using the Larch package and a Python program. The first step is to estimate spectral noise across a series of k-ranges with a fixed minimum value and identify the optimal maximum value in the k-range (k max ). The k max is determined by an empirical noise threshold that marks the point where the noise level in the Fourier transformed spectrum changes dramatically. Using the obtained k max value, the first shell is modeled to determine the minimum k value (k min ) by optimizing the background function through alignment of the spectrum with theory. The optimal k min corresponds to the point of the minimum R-factor, which quantifies the difference between the experimental and fitted spectrum. Our method was tested on various typical datasets and yielded suitable k-ranges for Fourier transformation and accurate first-shell fits. This approach helps avoid unreliable, irreproducible data analysis, especially for noisy data from diluted samples, and enables robust automatic first-shell EXAFS fitting.

EXAFS analysis↗
DOE OSTI2025

Amorphous zinc–molybdenum–sulfide chalcogel as a long-cycle, high-capacity electrode for lithium-ion batteries

The inherent limitations of intercalation-based electrodes in lithium-ion batteries have prompted the search for alternative materials with higher specific capacities and robust electrochemical stability. Sulfur-based electrodes, despite their high theoretical capacities (1672 mAh g −1 ), typically suffer from poor cycling performance. In this work, zinc molybdenum polysulfide (Zn x Mo 3 S 13 , 0.5 ≤ x), an amorphous semiconductor chalcogel, exhibits high specific capacity and excellent cycling stability. Synchrotron X-ray pair distribution function and extended X-ray absorption fine structure analyses reveal a short-range atomic structure comprising Mo–Mo, M–S (M = Mo, Zn), and S–S bonding motifs. The coordination environment of Mo and S closely resembles that of Mo 3 S 13 clusters, interconnected via S–S bridges and Zn 2+ cations. The Li/Zn x Mo 3 S 13 cell delivers an initial discharge capacity of 844 mAh g −1 at C/3, and retains 386.2 mAh g −1 after 1000 cycles with an average coulombic efficiency of 99.99%. The distribution of relaxation times analysis confirms the formation of a stable solid electrolyte interphase, which underpins the cell's long-term stability. In conclusion, this outstanding performance is attributed to the synergistic effects of the chalcogel's unique amorphous framework, semiconductive character, Zn-mediated polysulfide anchoring, and structural resilience, positioning Zn x Mo 3 S 13 chalcogel among the most durable pure metal sulfide cathodes reported for next-generation LIBs.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Composition dependence of atomic order in strain-relaxed, metastable GeSn alloys

Extended x-ray absorption fine structure (EXAFS) measurements of single-crystal Ge/GeSn radial heterostructure nanowires are used to examine the effects of composition on both short-range order (SRO) and longer-range disorder in GeSn alloys. GeSn has prompted significant interest because it can achieve a direct band gap for sufficient Sn concentrations beyond the equilibrium solid solubility limit in an all-group IV system. Short-range order in this material is particularly interesting as it has been predicted to affect the band gap independent of average composition or strain effects. By independently controlling the Sn composition and GeSn thickness during chemical vapor deposition of misfitting GeSn shells around ultrathin, elastically compliant, Ge core nanowires, the elastic misfit strain in the GeSn is minimized for Sn compositions over the studied range ≈Ge 0.96 Sn 0.04 to Ge 0.88 Sn 0.12 . The degree of SRO was found to decrease with increasing Sn composition. Additionally, damping of the EXAFS signal was observed as the Sn content increased, particularly for increasingly distant atomic shells about the absorbing atom, even for scattering paths not involving Sn atoms. This result is quantified as an increase in the mean-squared relative displacement parameters of the shells. These measurements reveal the accommodation of local strain due to the presence of the highly size-mismatched Sn atoms in the Ge diamond cubic lattice (≈14%), which may have effects on the band structure of the material in addition to the influence of short-range atomic order. Comparison among the nanowire samples allows for calculation of the topological rigidity parameter, a ∗∗ , for the first-neighbor bond lengths. Furthermore, these exhibit chemically distinct values for Ge-Ge, Ge-Sn, and Sn-Sn, and they are consistent with the value a ∗∗ = 0.75 ± 0.07 confirming the general applicability of the model to alloys with both large amounts of natural misfit strain and the potential for short-range order.

Crystal structure Semiconductors Transmission elec↗
DOE OSTI2026

Fast and accurate calculation of EXAFS Debye-Waller factors in U⁢O2 using the dynamical matrix method

Theoretical modeling of bonding dynamics in metal oxides is required for predicting their thermal conductivity, catalytic activity, and mechanical properties. A primary challenge is the scarcity of experimental methods for validating theoretical predictions of these atomic-scale dynamics. This work presents a workflow that uses experimental extended x-ray absorption fine structure (EXAFS) data collected at high temperatures to validate an interatomic force field for uranium dioxide (UO2), an important model material. The validated force field is then used to drive computationally intensive molecular dynamics (MD) simulations and as input for the much faster dynamical matrix Debye-Waller (DMDW) method. The predicted values of the Debye-Waller factors from the DMDW calculations are in good agreement with those obtained from the MD simulations, with residual pair-specific differences attributable to quantum zero-point motion at low temperatures and lattice anharmonicity at high temperatures. We further show that theoretical EXAFS spectra constructed directly from DMDW-derived Debye-Waller factors reproduce the experimental data (at relatively low temperatures) with accuracy comparable to full MD-EXAFS, providing an additional validation of the choice of the potential. This study establishes a validated, rapid computational pathway for modeling bond dynamics, naturally incorporating quantum nuclear\\\\r\\\\nstatistics absent in classical simulations, which are essential for the mechanistic understanding of complex oxide materials.

58 GEOSCIENCES↗
DOE OSTI2024

Silicate coprecipitation reduces green rust crystal size and limits dissolution-precipitation during air oxidation

Green rusts (GR) are mixed-valence iron (Fe) hydroxides which form in reducing redox environments like riparian and wetland soils and shallow groundwater. In these environments, silicon (Si) can influence Fe oxides’ chemical and physical properties but its role in GR formation and subsequent oxidative transformation have not been studied starting at initial nucleation. Green rust sulfate [GR(SO 4 )] and green rust carbonate [GR(CO 3 )] were both coprecipitated from salts by base titration in increasing % mol Si (0, 1, 10, and 50). The minerals were characterized before and after rapid (24 h) aqueous air-oxidation by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fe extended x-ray absorption fine structure spectroscopy (EXAFS), and N 2 -BET surface area. Results showed that only GR(SO4) or GR(CO3) was formed at every tested Si concentration. Increasing % mol Si caused decreased plate size and increased surface area in GR(CO3) but not GR(SO4). GR plate basal thickness was not changed at any condition indicating a lack of Si interlayering. Air oxidation of GR(SO4) at all % mol Si contents transformed by dissolution and reprecipitation into lepidocrocite and goethite, favoring ferrihydrite with higher % Si content. Air oxidation of GR(CO3) transformed into magnetite and goethite but increasing Si caused GR to oxidize while retaining its hexagonal plate structure via solid-state oxidation. Our results indicate that Si has the potential to cause GR to form in smaller particles and upon air oxidation, Si can either stabilize the plate structure or alter transformation to ferrihydrite.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The importance of electron scattering in the analysis of actinide X-ray spectroscopy

Abstract Manifestations of electron scattering in X-ray spectroscopy have been evident for decades. Here, it will be shown that the proper interpretation of variants of X-ray Absorption Spectroscopy (XAS) of actinide materials must include an accurate treatment of features caused by electron scattering, i.e., EXAFS or Extended X-ray Absorption Fine Structure. These EXAFS features can be of such low energy that they are within ten to twenty electron volts of the Unoccupied Density of States (UDOS), immediately above the Fermi Energy or Band Gap. The adaption of simple models using the FEFF simulation program will be presented, including the demonstration of the robust nature of the results from different models. Graphical abstract

Tobin, J. G. (ORCID:0000000322943301)↗
DOE OSTI2025

Plutonium Oxidation State Distribution in the Presence of WIPP-Relevant Organics and Iron Corrosion Products

The oxidation state and solubility of plutonium (Pu) in high ionic strength synthetic WIPP (Waste Isolation Pilot Plant) brines as a function of pC H+ in the presence and absence of WIPP-relevant organic ligands (EDTA [Ethylenediaminetetraacetic acid], oxalate, citrate, acetate) and iron corrosion products (magnetite and metallic iron) at 𝑇 = 23 ± 2 ∘C was thoroughly studied by long-term batch solubility experiments (between approximately 800-1,100 days) from an undersaturation approach. The oxidation state of Pu in the WIPP environment has been a topic of interest since the initial Compliance Certification Application (CCA). This study aims to investigate the solubility of Pu under the expected WIPP conditions and to determine the oxidation state of the solid phase that will control the solubility. One of the most important results of this study is that the Pu oxidation state was analyzed both from the surface area of the corrosion products and in the precipitated solid. The analysis of the Pu oxidation state on the surface of the iron mineral from the ongoing undersaturated experiments is more relevant to the performance assessment of nuclear waste disposal than short term batch (plutonium-iron phase) experiments. The X-ray Absorption Near-Edge Spectroscopy (XANES) analysis showed that Pu oxidation state is different on the metal surface and in the precipitated solid. Pu(III) is the dominant oxidation state in the metallic iron (Fe 0 ) system in the presence and absence of organics. Pu(IV) is the dominant oxidation state in the magnetite system in the presence and absence of organics. Also, organics stabilize Pu(IV) in the magnetite system. Analysis of Pu in the precipitated solid by Extended X-ray Absorption Fine Structure (EXAFS) analysis showed that Pu formed an inner-sphere complex with iron with minor amounts of PuO 2 present. X-ray diffraction (XRD) results indicate that metallic iron and magnetite did not oxidize in three years in the alkaline and high ionic strength system. Under these conditions (8 < pC H+ < 10 at T = (22 ± 2) °C under nitrogen atmosphere, the solubility of Pu changes by up to three orders of magnitude (10 -5 and 10 -8 M). The spread in solubility is highest at pC H+ = 9. Pu(III) and Pu(IV) showed different solubility behavior in the synthetic WIPP brine. A summary of the data collected in this report will be submitted to Sandia National Laboratories as part of a parameter update report which will outline the changes to the OXSTAT parameter for the 2026 Compliance Recertification Application (CRA-2026). The experiments performed were done according to the U.S. Department of Energy (DOE) approved Test Plan entitled “Effects of Radiolysis, Organic Complexation, and Redox Conditions on the Speciation and Oxidation State Distribution of Pu(III/IV)” (LCO-ACP-25). All data reported were obtained under the Los Alamos National Laboratory-Carlsbad Office (LANL-CO) Quality Assurance Program, which is compliant with the DOE Carlsbad Field Office, Quality Assurance Program Document (CBFO/QAPD).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1985

Iron impurities in Si3N4 processing

The atomic environment of iron impurities is investigated during the processing cycle of reaction-bonding silicon nitride (RBSN). Several analysis techniques are utilized, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and electron spin resonance (ESR), to examine iron impurities in the starting silicon powder, in sintered silicon compacts, and in RBSN materials. Results indicate that iron impurities in as-received metallurgical grade silicon powder are incorporated in the silicon bulk as a highly distorted FeSi2 compound. No surface iron or iron-based particulate is observed in the starting material. Upon sintering, the iron environment becomes an ordered FeSi2 structure. In the RBNS material, the FeSi2 structure is again distorted, as observed by both EXAFS and ESR.

Bouldin, C. E.↗
NASA NTRS1984

The nature of chemisorbed oxygen on Ni(100) and Cu(100)

Model calculations indicate two low-lying states for the interaction of O with Ni and Cu(100). The oxide state is approximately 1 eV more stable and its R(perpendicular) for Ni(100) is consistent with the experimental value for Ni(100), indicating only one type of stable chemisorption bond. This agrees with XPS (X-ray photoemission spectroscopy) and EXAFS (extended X-ray absorption fine structure) data for the observed LEED (low energy electron diffraction) structures. Interpretations of EELS (electron energy loss spectroscopy) data in terms of a radical state forthe p(2x2) and the oxide state for the c(2x2) structure must be seriously questioned.

Bauschlicher, C. W., Jr.↗
NASA NTRS1985

Studies of the Si/SiO2 interface using synchrotron radiation

Synchrotron radiation photoemission spectroscopy (SRPS) in the 1-4 KeV photon energy range is a useful tool for interface characterization. Results are presented of a series of studies of the near-interface region of Si/SiO2 which confirm that a bond strain gradient exists in the oxide as a result of lattice mismatch. These experiments include measurement of photoemission lineshape changes as a function of photon energy, corresponding changes in the electron escape depth near the interface, and surface extended X-ray absorption fine structure (SEXAFS) measurements directly indicating the shortening of the Si-Si second nearest neighbor distance in the near-interface region of the oxide.

Hecht, M. H.↗
DOE OSTI2025

Open‐Air Combustion Synthesis with Rapid Plasma Processing of Large‐Area Transparent Conducting Oxides

A vacuum-free, high-throughput synthesis of indium tin oxide (ITO) via Combustion Oxidation with Rapid Plasma Processing (CORP) utilizes a solution-based exothermic combustion reaction to generate the oxide with tunable control of either amorphous or crystalline phases. A subsequent open-air, forming gas plasma treatment is used to introduce oxygen vacancies and promote crystallization. Here, the evolution of the oxide structure is elucidated by extended X-ray absorption spectroscopy fine structure analysis. Using CORP, fabrication of 300 cm 2 of ITO possessing a champion sheet resistance of 38 Ω sq. −1 , visible transmission of 89%, conductivity stability for over 250 days, roughness < 2nm, and Haacke figure of merit (%T 550nm 10 /R s ) of 0.012 Ω −1 is achieved. Cost modeling of CORP demonstrates up to a 67% reduction in price for TCOs using fully continuous, in-line unit operations compared with vacuum sputtering. The work shows a path toward a low-cost, vacuum-free manufacturing method for TCOs at commercial scales.

42 ENGINEERING↗
DOE OSTI2024

Spectroscopic Signature of Metal-hydroxo and Peroxo Species in K-edge X-ray Absorption Spectra

Metal-dioxygen species are important intermediates formed during dioxygen activations by metalloenzymes in various biological processes, by catalysts in fuel cells, and prior to O 2 evolution by photosystem II. In this work, we focus on manganese-porphyrin complexes using tetramesitylporphyrin ligand (TMP) to explore changes in Mn K-edge X-ray absorption spectroscopy (XAS) associated with the formation of Mn-hydroxide and Mn–O 2 peroxide species. With limited spectroscopic characterization of these compounds, Mn K β X-ray emission spectroscopy (XES), XAS, density functional theory (DFT), and time-dependent DFT (TD-DFT) analysis will enhance our understanding of their complex electronic structure. We show that the shape of the pre-edge in the K-edge Mn X-ray absorption near-edge structure (XANES) can serve as a spectroscopic signature of the Mn III -peroxo formation and thus can be used to track the presence of the side-on peroxide as an intermediate in time-resolved or in situ experiments. In conclusion, our results will help to further summarize the spectroscopic fingerprints for peroxo and hydroxo species, addressing the challenge of identifying the reactive metal species in catalytic reactions.

Extended X-ray absorption fine structure↗
DOE OSTI2025

Affinity for OH – Produces Four-Coordinated Zn 2+ Impurities in Hydrated Amorphous Calcium Carbonate

Using ab initio based molecular dynamics and electronic structure calculations, we show that Zn impurities in hydrated amorphous calcium carbonate (ACC) have a much lower coordination number than other divalent impurities due to covalent interactions between the 3d Zn shell and the oxygen atoms of the carbonate and water groups. Further, the local structure around Zn in ACC, including the predicted low coordination number, is confirmed by X-ray absorption spectroscopy of synthetic Zn-bearing ACC. The strong Zn–O chemical interaction leads to substantial water dissociation and slightly disrupts the hydrogen bonding network. Implications of Zn 2+ incorporation for ACC stability are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

In Situ EXAFS Study of Mo–P Bond Dynamics in Molybdenum Phosphide during CO 2 Reduction and Hydrogen Evolution

Transition Metal Phosphides (TMPs) are widely studied as catalysts in reactions like hydrogen evolution, oxygen reduction, and hydrodesulfurization. TMPs have demonstrated remarkable efficiency in accelerating reactions by providing active sites for adsorption and facilitating the transformation of reaction intermediates, a feature that has increased the interest of TMPs in the electrochemical carbon dioxide reduction reaction (eCO 2 RR). Despite their growing use, the potential-dependent structural behavior of TMPs under operating electrochemical conditions remains insufficiently understood. This work investigates the dynamics of the Mo−P bond during eCO 2 RR and hydrogen evolution reaction (HER) using in situ extended X-ray absorption spectroscopy (EXAFS) studies at the Mo−K edge. Structural characterization of the synthesized MoP nanoparticles was performed by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results of the overall electrochemical activity of MoP are presented through linear sweep voltammetry (LSV) experiments in the potential range of 0 to −1.5 V versus Ag/AgCl and chronoamperometry (CA). Liquid products were analyzed by 1 H NMR spectroscopy. The synthesized catalyst showed increasing activity with the highest Faradaic efficiency of 11.75% for C 2+ products at −1.3 V vs Ag/AgCl. In situ EXAFS revealed a change in the average Mo−P bond distance during eCO 2 RR, whereas no such change was observed during the hydrogen evolution reaction (HER). This finding suggests that phosphorus, particularly through modulation of the Mo−P bond length, plays an important role in the eCO 2 RR and demonstrates how in situ EXAFS can track local structural perturbations in MoP catalysts during electrochemical operation, providing complementary structural insight that correlates with electrochemical behavior.

Catalysts↗
DOE OSTI2025

Dynamics of disordered intermediates during the two-electron alkaline MnO 2 conversion reaction for grid-scale batteries

Battery technologies beyond Li-ion are likely needed for extensive integration of grid-scale storage. The rechargeable Zn-MnO 2 chemistry has the potential for high sustainability, high safety, and low cost, using Earth-abundant basis materials. In an alkaline electrolyte, the MnO 2 cathode can cycle reversibly if modified by including a Bi-containing additive, although the cycling mechanism remains mostly unknown. This work presents an account of the intermediate species involved in the electrochemical transformation from layered δ-MnO 2 to Mn(OH) 2 and back. During charge, a disordered intermediate with a structure resembling layered β-MnOOH exists stably for an extended period, corresponding to a regime known to have unexpected electrochemical activity of Bi. During discharge, β-MnOOH exists only briefly and is never the majority material, revealing that the cycling mechanism is asymmetric. In conclusion, these findings represent a significant advance in mechanistic knowledge and can enable engineering to develop the system for commercial use.

36 MATERIALS SCIENCE↗