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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Pressure-Induced Phase Transitions in Bilayer La 3 Ni 2 O 7

La 3 Ni 2 O 7 differs from expectations in part because at ambient pressure, it exists in two polymorphs: an unconventional crystal structure with alternating layers of single- and triple-layered nickel−oxygen octahedra (i.e., La 2 NiO 4 plus La 4 Ni 3 O 10 , with the so-called 1313 crystal structure) and a classical double-layer Ruddlesden−Popper phase (i.e., La 3 Ni 2 O 7 , with the so-called 2222 crystal structure, which dominates at high pressure). In this study, we report the pressure-dependent structural and electrical resistive properties of single crystals of the classical double-layered La 3 Ni 2 O 7 , grown at slightly elevated pressure using the floating-zone method. Structural characterization under pressures up to 15.4 GPa reveals a gradual transition from orthorhombic to tetragonal symmetry that is completed at 12−14 GPa. Additionally, we present pressure and field-dependent electrical resistance measurements up to 27.4 GPa, from which we construct a phase diagram. Although a resistive transition at 80 K is observed at high pressures, the resistive hallmarks of superconductivity are not.

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

New Type of 2D Perovskites with Alternating Cations in the Interlayer Space, (C(NH 2 ) 3 )(CH 3 NH 3 ) n Pb n I 3 n +1 : Structure, Properties, and Photovoltaic Performance

In this study, we present the new homologous series (C(NH 2 ) 3 )(CH 3 NH 3 ) n Pb n I3 n+1 (n = 1, 2, 3) of layered 2D perovskites. Structural characterization by single-crystal X-ray diffraction reveals that these compounds adopt an unprecedented structure type, which is stabilized by the alternating ordering of the guanidinium and methylammonium cations in the interlayer space (ACI). Compared to the more common Ruddlesden–Popper (RP) 2D perovskites, the ACI perovskites have a different stacking motif and adopt a higher crystal symmetry. The higher symmetry of the ACI perovskites is expressed in their physical properties, which show a characteristic decrease of the bandgap with respect to their RP perovskite counterparts with the same perovskite layer thickness (n). The compounds show a monotonic decrease in the optical gap as n increases: E g = 2.27 eV for n = 1 to E g = 1.99 eV for n = 2 and E g = 1.73 eV for n = 3, which show slightly narrower gaps compared to the corresponding RP perovskites. First-principles theoretical electronic structure calculations confirm the experimental optical gap trends suggesting that the ACI perovskites are direct bandgap semiconductors with wide valence and conduction bandwidths. To assess the potential of the ACI perovskites toward solar cell applications, we studied the (C(NH 2 ) 3 )(CH 3 NH 3 ) 3 Pb 3 I 10 (n = 3) compound. Compact thin films from the (C(NH 2 ) 3 )(CH 3 NH 3 ) 3 Pb 3 I 10 compound with excellent surface coverage can be obtained from the antisolvent dripping method. Planar photovoltaic devices from optimized ACI perovskite films yield a power-conversion-efficiency of 7.26% with a high open-circuit voltage of ~1 V and a striking fill factor of ~80%.

14 SOLAR ENERGY↗
DOE OSTI2020

Electronic structure and oxophilicity optimization of mono-layer Pt for efficient electrocatalysis

The slow kinetics of the anodic hydrogen oxidation reaction (HOR) in alkaline medium is one of the limitations for anion exchange membrane fuel cells (AEMFCs). Hence, accurately regulate and understand catalytic interface structure are essential to solve this bottleneck and reveal the structure-activity relationship. In this work, a novel trimetal core-shell model with mono-layer Pt-shell is employed for hydrogen electrooxidation to avoid thermodynamic driven bulk/surface composition deviation. On account of the atomic radius discrepancies of 3d-transition metals M (M = Fe, Co and Cu), the electronic structure of mono-layer Pt is regulated by the strain-engineered Pd-M core and the electrocatalytic activity for HOR is tuned accordingly. Nevertheless, step-by-step electrochemical monitoring and surface-treatment experiments indicate that the oxophilicity optimization by low-valence M(OH) x species, rather than the hydrogen binding energy (HBE) optimization caused by strain engineering, influence the activity obviously. It is mainly derived from the enhanced adsorption of OH ad and accelerated desorption of the H ad . The trimetal core-shell model breathes new life into the low-Pt catalyst design for hydrogen electrooxidation reaction.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Crystal and Electronic Structure of High-Temperature Superconductive Layered Cuprates in Temperature Interval 100–300 K

For two HTSC materials, Y{sub 1−x}Ca{sub x}Ba{sub 2}Cu{sub 3}O{sub 6.7} and Tl{sub 0.8}Hg{sub 0.2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8.15}, their crystal structure has been studied earlier in the temperature interval 100–300 K. It is shown that for both compounds, the height of CuO{sub 5} pyramids has a minimum in temperature interval from ∼ 150 to ∼ 250 K. The electronic structure is calculated using first principles based on the obtained data of crystal structure. It is revealed that a decrease in the CuO{sub 5} pyramid height leads to the appearance of the electronic state density peak with an energy of 0.3–0.4 eV under Fermi level. Localized states of barium and apical oxygen make the main contribution to this peak. By reduction the temperature below ∼ 150 K, these localized electronic states disappear, and under continuous cooling, the superconductivity appears.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Iron arsenides with three-dimensional FeAs layer networks: Can(n+1)/2(Fe1-xPtx)(2+3n)Ptn(n-1)/2As(n+1)(n+2)/2 (n=2, 3)

We report the comprehensive studies between synchrotron X-ray diffraction, electrical resistivity and magnetic susceptibility experiments for the iron arsenides Can(n+1)/2(Fe1-xPtx)(2+3n)Ptn(n -1)/2As(n+1)(n+2)/2 for n=2 and 3. Both structures crystallize in the monoclinic space group P21/m (#11) with three-dimensional FeAs structures. The horizontal FeAs layers are bridged by inclined FeAs planes through edge-sharing FeAs5 square pyramids, resulting in triangular tunneling structures rather than the simple layered structures found in conventional iron arsenides. n=3 system shows a sign of superconductivity with a small volume fraction. Our first-principles calculations of these systems clearly indicate that the Fermi surfaces originate from strong Fe-3d characters and the three-dimensional nature of the electric structures for both systems, thus offering the playgrounds to study the effects of dimensionality on high Tc superconductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Pressure Impact on the Crystal Structure, Optical, and Transport Properties in Layered Oxychalcogenides BiCu Ch O( Ch = S, Se)

The layered oxychalcogenides BiCuChO (Ch = S, Se, Te) represent a unique family of two-dimensional semiconductors with extraordinary optoelectronic and thermoelectric properties. Chemical strategies such as elemental doping have been used to modify their crystal structures and electronic configurations for better photocatalytic performances. Herein, we report the pressure impact on the crystalline and electronic band structures of BiCuChO (Ch = S, Se) with in situ synchrotron X-ray diffraction, Raman spectroscopy, electric resistivity and photocurrent measurements, and first-principle calculations. Under pressure, the crystalline lattices shrink continuously without symmetry breaking, which enhances the crystal field splitting; on the other hand, the pressure-induced charge delocalization causes the band broadening. The competition between the crystal field and charge delocalization demonstrates an efficient tool for band gap engineering: the electrical conductivity is enhanced below 12 GPa and monotonically decreases up to 40 GPa. In addition, BiCuSeO exhibits considerable photocurrent up to ~40 GPa, which suggests its potential application in pressure-responsive optoelectrical devices. Lastly, the comprehensive studies of the pressure effect on the crystal structure and electronic properties in two-dimensional semiconductors provide and in-depth understanding for developing new optoelectronic materials under extreme conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Structure and reactivity of highly reduced titanium oxide surface layers on TiO 2 : A first-principles study

Titanium oxide structures featuring highly reduced TiO x films on top of nearly stoichiometric TiO 2 hold promise for applications ranging from photocatalysis to resistance switching devices. In this article, we focus on titanium monoxide (TiO) layers on anatase TiO 2 (001) and use first principles calculations to investigate their structure and properties as well as their interface with liquid water. We find that only a single TiO layer can grow epitaxially on anatase (001) and subsequent growth leads to the formation of TiO islands. The TiO layers decrease the work function and enhance the surface conductivity in comparison to pure anatase, two features that can improve the TiO 2 performance in photocatalytic hydrogen evolution but are thermodynamically unstable relative to pure TiO 2 in humid/aqueous environment. Furthermore, first principles molecular dynamics simulations of the TiO (001)-water and anatase (001)-water interfaces show that unlike the multilayer structure of interfacial water on the anatase surface, a very dense and tightly packed first water layer is present on the surface of TiO, which could represent the first stage of partial surface reoxidation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Composition and in situ structure of the Methanospirillum hungatei cell envelope and surface layer

Archaea share genomic similarities with Eukarya and cellular architectural similarities with Bacteria, though archaeal and bacterial surface layers (S-layers) differ. Using cellular cryo–electron tomography, we visualized the S-layer lattice surroundingMethanospirillum hungatei, a methanogenic archaeon. Though more compact than known structures,M. hungatei’s S-layer is a flexible hexagonal lattice of dome-shaped tiles, uniformly spaced from both the overlying cell sheath and the underlying cell membrane. Subtomogram averaging resolved the S-layer hexamer tile at 6.4-angstrom resolution. By fitting an AlphaFold model into hexamer tiles in flat and curved conformations, we uncover intra- and intertile interactions that contribute to the S-layer’s cylindrical and flexible architecture, along with a spacer extension for cell membrane attachment.M. hungateicell’s end plug structure, likely composed of S-layer isoforms, further highlights the uniqueness of this archaeal cell. These structural features offer advantages for methane release and reflect divergent evolutionary adaptations to environmental pressures during early microbial emergence.

Science & Technology - Other Topics↗
DOE OSTI2017

eQE: An open‐source density functional embedding theory code for the condensed phase

Abstract In this work, we present the main features and algorithmic details of a novel implementation of the frozen density embedding (FDE) formulation of subsystem density functional theory (DFT) that is specifically designed to enable ab initio molecular dynamics (AIMD) simulations of large‐scale condensed‐phase systems containing 1000s of atoms. This code (available at http://eqe.rutgers.edu ) has been given the moniker of embedded Quantum ESPRESSO (eQE) as it is a generalization of the open‐source Quantum ESPRESSO (QE) suite of programs. The strengths of eQE reside in a hierarchical parallelization scheme that allows for an efficient and fully self‐consistent treatment of the electronic structure (via the addition of an additional DIIS extrapolation layer) while simultaneously exploiting the inherent symmetries and periodicities in the system (via sampling of subsystem‐specific first Brillouin zones and utilization of subsystem‐specific basis sets). While bulk liquids and molecular crystals are two classes of systems that exemplify the utility of the FDE approach (as these systems can be partitioned into weakly interacting subunits), we show that eQE has significantly extended this regime of applicability by outperforming standard semilocal Kohn–Sham DFT (KS‐DFT) for large‐scale heterogeneous catalysts with quite different layer‐specific electronic structure and intrinsic periodicities. eQE features very favorable strong parallel scaling for a model system of bulk liquid water composed of 256 water molecules, which allows for a significant decrease in the overall time to solution when compared to KS‐DFT. We show that eQE achieves speedups greater than one order of magnitude ( ) when performing AIMD simulations of such large‐scale condensed‐phase systems as: (1) molecular liquids via bulk liquid water represented by 1024 independent water molecules (3072 atoms with a 25.3× speedup over KS‐DFT), (2) polypeptide/biomolecule solvation via ( gly ) 6 solvated in (H 2 O) 395 (1230 atoms with a 38.6× speedup over KS‐DFT), and (3) molecular crystals via a 3 × 3 × 3 periodic supercell of pentacene (1940 atoms with a 12.0× speedup over KS‐DFT). These results represent a significant improvement over the current state‐of‐the‐art and now enable subsystem DFT‐based AIMD simulations of realistically sized condensed‐phase systems of interest throughout chemistry, physics, and materials science.

Genova, Alessandro↗
DOE OSTI2017

Characterization and differentiation of rock varnish types from different environments by microanalytical techniques

We investigated rock varnishes collected from several locations and environments worldwide by a wide range of microanalytical techniques. These techniques were selected to address the challenges posed by the chemical and structural complexity within the micrometer- to nanometer-sized structures in these geological materials. Femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs LA-ICP-MS), scanning transmission X-ray microscopy-near edge X-ray adsorption fine structure spectroscopy (STXM-NEXAFS) in combination with scanning electron microscopy (SEM) of focused ion beam (FIB) ultra-thin (100–200 nm) sections, conventional and polarization microscopy, as well as electron paramagnetic resonance (EPR) measurements were used to obtain information about these rock varnishes. Rock varnishes from different environments, which cannot readily be distinguished based on their macroscopic appearance, differ significantly in their constituent elemental mass fractions, e.g., of Mn, Fe, Ni, Co, Ba, and Pb, and their rare earth element (REE) patterns. Structural characteristics such as the particle sizes of embedded dust grains, internal structures such as layers of Mn-, Fe-, and Ca -rich material, and structures such as cavities varied between varnishes from different environments and regions in the world. The EPR spectra were consistent with aged biogenic Mn oxides in all samples, but showed subtle differences between samples of different origin. Our observations allow us to separate rock varnishes into different types, with differences that might be indicators of distinct geneses. Five different types of rock varnish could be distinguished, Type I–V, of which only Type I might be used as potential paleoclimate archive. Each varnish type has specific characteristics in terms of their elemental composition, element distribution, and structures. The combination of element ratios (Mn/Ba, Al/Ni, Mn/REY, Mn/Ce, Mn/Pb, La N /Yb N , and Ce/Ce*), total REE contents, and structures can be used to separate the different types of rock varnish from each other.

58 GEOSCIENCES↗
DOE OSTI2018

Correlation between long range and local structural changes in Ni-rich layered materials during charge and discharge process

Ni-rich cathode materials can deliver higher energy density with a lower cost compared with other conventional layered oxide materials. However, the cycling performance of Ni-rich materials needs further improvement, and the irreversible phase transformation related to the cell failure is not fully understood yet. Although an H1-H2-H3 structural change process is revealed, a more specific explanation about the difference of these hexagonal phases is needed for deeper comprehension and further targeted modification of Ni-rich materials. In this work, the different phase transformation mechanisms of LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) and LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) are investigated by C X-ray diffraction (XRD) measurement, and the relationship between structural change and capacity degradation is discussed, showing that H3 phase can be harmful for cycling. In addition, Li-6 solid state nuclear magnetic resonance (ss-NMR) experiments are carried out for detecting the Li chemical environment at different state of charge, and the data can be associated with structural change obtained from in operando XRD results. From the analysis mentioned above, a new explanation of H1/H2/H3 is given, and a relationship between long range and local structural change has been put forward for the first time.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Irradiation-Induced Structural Disorder and Its Influence on the Mechanical Response of Polycrystalline MoS2

Molybdenum disulfide (MoS2) thin films are widely used as dry-film lubricants and protective coatings in aerospace and other radiation-exposed environments. Conventional synthesis routes produce polycrystalline films whose grain boundaries and other native defects cause their mechanical and tribological behavior to differ substantially from that of ideal single crystals. Under irradiation, these films progressively evolve from polycrystalline structures, composed of layered MoS2 grains, into highly disordered and eventually amorphous structures, altering both their tribological performance and mechanical integrity. Here, we employ reactive atomistic simulations to investigate irradiation-driven structural evolution in bulk polycrystalline MoS2. Using controlled primary knock-on atom (PKA) events, we characterize the progressive transition from a polycrystalline microstructure to an amorphous network by tracking defect accumulation and structural disorder. We then establish how this transition modifies the dominant deformation mechanisms and the temperature-dependent tensile response. Specifically, irradiation suppresses interlayer sliding and delamination, mechanisms which facilitate the deformation of the pristine polycrystal, resulting in defect-induced hardening. Broadly, our results establish direct process–structure–property relationships linking irradiation-induced defect accumulation, microstructural evolution, deformation mechanisms, and mechanical behavior, providing an atomistic framework for understanding the structural integrity and long-term reliability of irradiated MoS2 coatings.

Moore, Daniel [Sandia National Laboratories (SNL)]↗
DOE OSTI2020

Prediction of superconductivity and topological aspects in single-layer β -Bi 2 Pd

Topological superconductors, characterized by topologically nontrivial states residing in a superconducting gap, are a recently discovered class of materials having Majorana fermions. The interplay of superconductivity and topological states gives rise to opportunities for achieving such topological superconductors in condensed matter systems. Up to now, several single-material topological superconductors in this form have been theoretically predicted and experimentally confirmed. Here, using the first-principles calculations, we study the superconducting single-layer β-Bi 2 Pd. In this work, the electronic density of states near Fermi level of this monolayer are dominated by the Bi-p and Pd-d orbitals, forming a two-band Fermi surface with multiclass sheets. The presence of soft phonon bands, in cooperation with the electron susceptibility, accounts for electron-phonon superconductivity of single-layer β-Bi 2 Pd. With the centrosymmetric structure, single-layer β-Bi 2 Pd possesses a continuous gap over the whole Brillouin zone and topological Dirac-like states at its one-dimensional boundary. The present findings would lead to the expectation of one-dimensional topological superconductivity and Majorana bound states in a monolayer candidate of β-Bi 2 Pd with intrinsic full-gap superconductivity.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Kinematic analysis of Hurricane Frederick (1979) using satellite, aircraft and Rawinsonde data

Results of kinematic analyses of Hurricane Frederick (1979) performed using satellite wind vectors, aircraft measurements and rawinsonde data are presented. The data were gathered, reduced, preliminarily integrated and used to analyze the structure of the storm in the inflow and outflow layers. The mean structure at large radii is in good agreement with composite analyses of tropical cyclones. Changes in the storm structure from 11 to 12 Sep. 1979 suggest that remote sensing techniques are useful in monitoring storm intensity. A more sophisticated integration of the various data, including determination of optimum heights for satellite wind vectors, is underway.

Frank, W. M.↗
NASA NTRS1984

Kinematic analysis of Hurricane Frederick (1979) using satellite, aircraft and rawinsonde data

Results of kinematic analyses of Hurricane Frederick (1979) performed using satellite wind vectors, aircraft measurements and rawinsonde data are presented. The data were gathered, reduced, preliminarily integrated and used to analyze the structure of the storm in the inflow and outflow layers. The mean structure at large radii is in good agreement with composite analyses of tropical cyclones. Changes in the storm structure from 11 to 12 Sep. 1979 suggests that remote sensing techniques may be useful in monitoring storm intensity.

Frank, W. M.↗
NASA NTRS1988

Interactions of silicate glasses with aqueous environments under conditions of prolonged contact and flow

This paper discusses mechanisms involving saturation and reactions that lead to the formation of altered phases in silicate glasses considered for use in geologic repositories for nuclear waste. It is shown that the rate of dissolution of silicate glasses exposed to a broad range of contact times, leachant compositions, and surface-to-volume ratios is strongly affected by the presence of reactive species such as Al, Mg, and Fe. The reactive materials may originate in the leachant or, under conditions of high surface-to-volume ratio, in the glass itself. The effects of glass composition on the course of the corrosion process can be viewed in terms of the formation of a surface layer on the leached glass; the type, composition, and structure of this layer control the dissolution behavior of the glass.

Barkatt, Aaron↗
DOE OSTI2021

Study of the crystal structure of SnS thin films by atomic layer deposition

Tin monosulfide, SnS, absorbs visible light and holds promise for thin-film photovoltaics. However, the optoelectronic properties of this material vary among the different structural phases, and control over the phase of vapor deposited SnS thin films is not well understood. In order to study the phases and crystallographic orientations of SnS films, films with thicknesses of 90 nm–750nm were prepared by atomic layer deposition (ALD) at temperatures between 80 °C and 200 °C on amorphous silicon dioxide (a-SiO2) and single-crystal sodium chloride (NaCl). We show that the crystal structures and orientations of the ALD-SnS thin films vary with deposition temperature, film thickness, and substrate. We confirm the presence of metastable cubic π-SnS in co-existence with the thermodynamically stable orthorhombic α-SnS and find that the π phase is more prevalent at lower deposition temperatures. The films grown on a-SiO2 are textured, the degree of texturing increases with lower temperature or higher thickness, and the deposited phase is also thickness dependent. Upon annealing, which is known to promote SnS grain growth, all films revert to orthorhombic α-SnS. The films grown on the NaCl(100) substrate exhibit a much higher degree of texturing and show different preferred orientations dependent on the phase: π-(400) and α-(111) or α-(040). In addition, we demonstrate a proof-of-concept device made from the highly oriented SnS grown on NaCl.

36 MATERIALS SCIENCE↗

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