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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Nature of S-States in the Oxygen-Evolving Complex Resolved by High-Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy

Photosystem II, the water splitting enzyme of photosynthesis, utilizes the energy of sunlight to drive the four-electron oxidation of water to dioxygen at the oxygen-evolving complex (OEC). The OEC harbors a Mn 4 CaO 5 cluster that cycles through five oxidation states S i (i = 0–4). The S 3 state is the last metastable state before the O 2 evolution. Its electronic structure and nature of the S 2 → S 3 transition are key topics of persisting controversy. Most spectroscopic studies suggest that the S 3 state consists of four Mn(IV) ions, compared to the Mn(III)Mn(IV) 3 of the S 2 state. However, recent crystallographic data have received conflicting interpretations, suggesting either metal- or ligand-based oxidation, the latter leading to an oxyl radical or a peroxo moiety in the S 3 state. Herein, we utilize high-energy resolution fluorescence detected (HERFD) X-ray absorption spectroscopy to obtain a highly resolved description of the Mn K pre-edge region for all S-states, paying special attention to use chemically unperturbed S 3 state samples. In combination with quantum chemical calculations, we achieve assignment of specific spectroscopic features to geometric and electronic structures for all S-states. These data are used to confidently discriminate between the various suggestions concerning the electronic structure and the nature of oxidation events in all observable catalytic intermediates of the OEC. Our results do not support the presence of either peroxo or oxyl in the active configuration of the S 3 state. This establishes Mn-centered storage of oxidative equivalents in all observable catalytic transitions and constrains the onset of the O–O bond formation until after the final light-driven oxidation event.

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

The classical-to-quantum crossover in the strain-induced ferroelectric transition in SrTiO3 membranes

Mechanical strain presents an effective control over symmetry-breaking phase transitions. In quantum paralelectric SrTiO3, strain can induce ferroelectric order via modification of the local Ti potential energy landscape. However, brittle bulk materials can only withstand limited strain range (~0.1%). Taking advantage of nanoscopically-thin freestanding membranes, we demonstrate an in- situ strain-induced reversible ferroelectric transition in freestanding SrTiO3 membranes. We measure the ferroelectric order by detecting the local anisotropy of the Ti 3d orbital signature using x-ray linear dichroism at the Ti-K pre-edge, while the strain is determined by x-ray diffraction. With reduced thickness, the SrTiO3 membranes remain elastic with >1% tensile strain cycles. A robust displacive ferroelectricity appears beyond a temperature-dependent critical strain. Interestingly, we discover a crossover from a classical ferroelectric transition to a quantum regime at low temperatures, which enhances strain-induced ferroelectricity. Our results offer new opportunities to strain engineer functional properties in low dimensional quantum materials and provide new insights into the role of ferroelectric fluctuations in quantum paraelectric SrTiO3.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Spontaneous orbital polarization in the nematic phase of FeSe

The origin of nematicity in FeSe remains a critical outstanding question towards understanding unconventional superconductivity in proximity to nematic order. To understand what drives the nematicity, it is essential to determine which electronic degree of freedom admits a spontaneous order parameter independent from the structural distortion. In this work, we use X-ray linear dichroism at the Fe K pre-edge to measure the anisotropy of the 3d orbital occupation as a function of in situ applied stress and temperature across the nematic transition. Along with using X-ray diffraction to precisely quantify the strain state, we reveal a lattice-independent, spontaneously ordered orbital polarization within the nematic phase, as well as an orbital polarizability that diverges as the transition is approached from above. These results provide strong evidence that spontaneous orbital polarization serves as the primary order parameter of the nematic phase.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K by Materials Project

K crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded to eight equivalent K atoms to form distorted edge-sharing KK8 hexagonal bipyramids. All K–K bond lengths are 4.51 Å. In the second K site, K is bonded in a distorted hexagonal planar geometry to six K atoms. There are a spread of K–K bond distances ranging from 4.28–4.46 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Reactivity of Shale to Supercritical CO 2 : Insights from Microstructural Characterization and Mineral Phase Evolution in Caney Shales for CCUS Applications

Understanding mineral–fluid interactions in shale under supercritical CO 2 (scCO 2 ) conditions is relevant for assessing long-term geochemical containment. This study characterizes mineralogical transformations and elemental redistribution in five Caney Shale samples serving as proxies for reservoir (R1, R2, R3) and caprock (D1, D2) facies, subjected to 30-day static exposure to pure scCO 2 at 60 °C and 17.23 MPa (2500 psi), with no brine or impurities introduced. SEM-EDS analyses were conducted before and after exposure, with mineral phases classified into silicates, carbonates, sulfides, and organic matter. Initial compositions were dominated by quartz (38–47 wt.%), illite (16–23 wt.%), carbonates (12–18 wt.%), and organic matter (8–11 wt.%). Post-exposure, carbonate loss ranged from 15 to 40% in reservoir samples and up to 20% in caprock samples. Illite and K-feldspar showed depletion of Fe 2+ , Mg 2+ , and K + at grain edges and cleavages, while pyrite underwent oxidation with Fe redistribution. Organic matter exhibited scCO 2 -induced surface alteration and apparent sorption effects, most pronounced in R2 and R3. Elemental mapping revealed Ca 2+ , Mg 2+ , Fe 2+ , and Si 4+ mobilization near reactive interfaces, though no secondary mineral precipitates formed. Reservoir samples developed localized porosity, whereas caprock samples retained more structural clay integrity. The results advance understanding of mineral reactivity and elemental fluxes in shale-based CO 2 sequestration.

geochemical CO2 sequestration↗
DOE OSTI2020

Deactivation of Cu-Exchanged Automotive-Emission NH 3 -SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO x with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of Cu II to Cu I and Cu x O y was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated Cu II sites trumps that of Brønsted acid sites for NH 3 -SCR activity.

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

Amorphous K–Co–Mo–S x Chalcogel: A Synergy of Surface Sorption and Ion-Exchange

Chalcogel represents a unique class of meso- to macroporous nanomaterials that offer applications in energy and environmental pursuits. We report the synthesis of an ion-exchangeable amorphous chalcogel using a nominal composition of K 2 CoMo 2 S 10 (KCMS) at room temperature is reported. Synchrotron X-ray pair distribution function (PDF), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) reveal a plausible local structure of KCMS gel consisting of Mo 5+ 2 and Mo 4+ 3 clusters in the vicinity of di/polysulfides which are covalently linked by Co 2+ ions. The ionically bound K + ions remain in the percolating pores of the Co–Mo–S covalent network. XANES of Co K-edge shows multiple electronic transitions, including quadrupole (1s→3d), shakedown (1s→4p + MLCT), and dipole allowed 1s→4p transitions. Remarkably, despite a lack of regular channels as in some crystalline solids, the amorphous KCMS gel shows ion-exchange properties with UO 2 2+ ions. Additionally, it also presents surface sorption via [S∙∙∙∙UO 2 2+ ] covalent interactions. Overall, this study underscores the synthesis of quaternary chalcogels incorporating alkali metals and their potential to advance separation science for cations and oxo-cationic species by integrating a synergy of surface sorption and ion-exchange.

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

Materials Data on K by Materials Project

K crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. there are two inequivalent K sites. In the first K site, K is bonded to twelve equivalent K atoms to form a mixture of face and edge-sharing KK12 cuboctahedra. All K–K bond lengths are 4.68 Å. In the second K site, K is bonded in a 6-coordinate geometry to six K atoms. Both K–K bond lengths are 4.18 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2CuPb(NO2)6 by Materials Project

K2PbCu(NO2)6 crystallizes in the cubic F23 space group. The structure is three-dimensional and consists of four copper molecules and one K2Pb(NO2)6 framework. In the K2Pb(NO2)6 framework, there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to twelve equivalent O2- atoms to form edge-sharing KO12 cuboctahedra. All K–O bond lengths are 2.92 Å. In the second K1+ site, K1+ is bonded to twelve equivalent O2- atoms to form edge-sharing KO12 cuboctahedra. All K–O bond lengths are 3.21 Å. Pb2+ is bonded in a distorted q6 geometry to twelve equivalent O2- atoms. All Pb–O bond lengths are 2.72 Å. N3+ is bonded in a bent 120 degrees geometry to two equivalent O2- atoms. Both N–O bond lengths are 1.26 Å. O2- is bonded in a distorted single-bond geometry to two K1+, one Pb2+, and one N3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2Zn(CN)4 by Materials Project

K2Zn(CN)4 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional and consists of one K(CN)2 framework and eight zinc molecules. In the K(CN)2 framework, K1+ is bonded to six equivalent N3- atoms to form edge-sharing KN6 octahedra. All K–N bond lengths are 2.94 Å. C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. N3- is bonded to three equivalent K1+ and one C2+ atom to form a mixture of distorted corner and edge-sharing NK3C tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The O K -2 V spectrum of CO: the influence of the second core-hole

Using synchrotron radiation in the tender X-ray regime, a photoelectron spectrum showing the formation of single site double-core-hole pre-edge states, involving the K shell of the O atom in CO, has been recorded by means of high-resolution electron spectroscopy. The experimentally observed structures have been simulated, interpreted and assigned, employing state-of-the-art ab initio quantum chemical calculations, on the basis of a theoretical model, accounting for their so-called direct or conjugate character. Features appearing above the double ionization threshold have been reproduced by taking into account the strong mixing between multi-excited and continuum states. The shift of the σ* resonance below the double ionization threshold, in combination with the non-negligible contributions of multi-excited configurations in the final states reached, gives rise to a series of avoided crossings between the different potential energy curves.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Materials Data on K2Cd(CN)4 by Materials Project

K2Cd(CN)4 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional and consists of eight cadmium molecules and one K(CN)2 framework. In the K(CN)2 framework, K1+ is bonded to six equivalent N3- atoms to form distorted edge-sharing KN6 octahedra. All K–N bond lengths are 2.97 Å. C2+ is bonded in a single-bond geometry to one N3- atom. The C–N bond length is 1.17 Å. N3- is bonded to three equivalent K1+ and one C2+ atom to form a mixture of distorted corner and edge-sharing NK3C tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KTl2 by Materials Project

KTl2 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. K is bonded to six equivalent Tl atoms to form distorted edge-sharing KTl6 octahedra. All K–Tl bond lengths are 3.58 Å. Tl is bonded in a 6-coordinate geometry to three equivalent K and three equivalent Tl atoms. All Tl–Tl bond lengths are 3.28 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KCd(NO2)3 by Materials Project

K(NO2)3Cd crystallizes in the cubic Pm-3 space group. The structure is three-dimensional and consists of one cadmium molecule and one K(NO2)3 framework. In the K(NO2)3 framework, K1+ is bonded to twelve equivalent O2- atoms to form edge-sharing KO12 cuboctahedra. All K–O bond lengths are 3.46 Å. N3+ is bonded in a linear geometry to two equivalent O2- atoms. Both N–O bond lengths are 1.25 Å. O2- is bonded in a single-bond geometry to two equivalent K1+ and one N3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KAs4BrO6 by Materials Project

K(As2O3)2Br crystallizes in the hexagonal P6/mmm space group. The structure is two-dimensional and consists of one hydrobromic acid molecule and one K(As2O3)2 sheet oriented in the (0, 0, 1) direction. In the K(As2O3)2 sheet, K1+ is bonded to twelve equivalent O2- atoms to form edge-sharing KO12 cuboctahedra. All K–O bond lengths are 3.17 Å. As3+ is bonded in a distorted T-shaped geometry to three equivalent O2- atoms. All As–O bond lengths are 1.84 Å. O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+ and two equivalent As3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KAs4IO6 by Materials Project

K(As2O3)2I crystallizes in the hexagonal P6/mmm space group. The structure is two-dimensional and consists of one hydriodic acid molecule and one K(As2O3)2 sheet oriented in the (0, 0, 1) direction. In the K(As2O3)2 sheet, K1+ is bonded to twelve equivalent O2- atoms to form edge-sharing KO12 cuboctahedra. All K–O bond lengths are 3.19 Å. As3+ is bonded in a distorted T-shaped geometry to three equivalent O2- atoms. All As–O bond lengths are 1.84 Å. O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+ and two equivalent As3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KAs4ClO6 by Materials Project

(K(As2O3)2)2Cl2 crystallizes in the hexagonal P6/mmm space group. The structure is two-dimensional and consists of one hydrochloric acid molecule and one K(As2O3)2 sheet oriented in the (0, 0, 1) direction. In the K(As2O3)2 sheet, K1+ is bonded to twelve equivalent O2- atoms to form edge-sharing KO12 cuboctahedra. All K–O bond lengths are 3.17 Å. As3+ is bonded in a distorted T-shaped geometry to three equivalent O2- atoms. All As–O bond lengths are 1.84 Å. O2- is bonded in a distorted bent 120 degrees geometry to two equivalent K1+ and two equivalent As3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Atomistic Investigation of Plastic Deformation and Dislocation Motion in Uranium Mononitride

Uranium mononitride (UN) is a promising advanced nuclear fuel due to its high thermal conductivity and high fissile density. However, many aspects of its mechanical behavior, particularly at reactor-relevant conditions, remain unclear. In this study, molecular dynamics (MD) simulations were employed to investigate the deformation behavior and dislocation motion in UN. We found that the Kocevski potential predicts the principal slip system as $\frac{1}{2}$ $\langle110\rangle${110}, aligning with experimental data. On the other hand, the Tseplyaev potential predicts slip to primarily occur on $\frac{1}{2}$ $\langle110\rangle${111}. MD simulations of stress–strain behavior were used to estimate the nanoindentation hardness, revealing that the Kocevski potential accurately predicts hardness even though it fails to model dynamic plasticity. Complete dislocation mobility functions have been fitted for the edge and screw dislocations in both the thermally activated and phonon-drag regimes. The 300 K linear mobility of the edge dislocation using the Tseplyaev potential was found to be 817 Pa -1 ·s -1 , whereas that of the screw dislocation using the Kocevski potential was found to be 4546 Pa -1 ·s -1 . At intermediate stresses, we observed that the subsonic steady-state motion of the edge dislocation in UN is intermittently interrupted by velocity jumps, reaching the average sound velocity. Finally, the threshold Schmid stress is calculated as 179–197 MPa, which gives an upper-limit estimate of the uniaxial yield stress of polycrystalline UN of 548–603 MPa. These findings, including the fitted dislocation mobility function, provide essential input for future plasticity and dislocation dynamics models of nuclear fuels.

36 MATERIALS SCIENCE↗