Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Chemical structures”

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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Direct observation of elemental fluctuation and oxygen octahedral distortion-dependent charge distribution in high entropy oxides

The enhanced compositional flexibility to incorporate multiple-principal cations in high entropy oxides (HEOs) offers the opportunity to expand boundaries for accessible compositions and unconventional properties in oxides. Attractive functionalities have been reported in some bulk HEOs, which are attributed to the long-range compositional homogeneity, lattice distortion, and local chemical bonding characteristics in materials. However, the intricate details of local composition fluctuation, metal-oxygen bond distortion and covalency are difficult to visualize experimentally, especially on the atomic scale. Here, we study the atomic structure-chemical bonding-property correlations in a series of perovskite-HEOs utilizing the recently developed four-dimensional scanning transmission electron microscopy techniques which enables to determine the structure, chemical bonding, electric field, and charge density on the atomic scale. The existence of compositional fluctuations along with significant composition-dependent distortion of metal-oxygen bonds is observed. Consequently, distinct variations of metal-oxygen bonding covalency are shown by the real-space charge-density distribution maps with sub-ångström resolution. The observed atomic features not only provide a realistic picture of the local physico-chemistry of chemically complex HEOs but can also be directly correlated to their distinctive magneto-electronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Solid-State Pathway Control via Reaction-Directing Heteroatoms: Ordered Pyridazine Nanothreads through Selective Cycloaddition

Nanothreads are one-dimensional nanomaterials comprised of a primarily sp 3 hydrocarbon backbone. They are typically formed through cycloaddition reactions induced by compression of small molecules to high pressures. Although nanothreads have been synthesized from a range of small molecule precursors (e.g., benzene, pyridine, aniline), the ability to control reaction pathways to produce atomically precise nanothreads with distinct chemical structures remains a difficult challenge. In this study, we show how heteroatoms incorporated within starting precursors can serve as “thread directing” groups by selecting for specific cycloaddition reaction pathways. By using a less-reactive diazine group within a six-membered aromatic ring, we successfully predict and synthesize the first carbon nanothread material derived from pyridazine (1,2-diazine, C 4 H 4 N 2 ). Compared with previous nanothreads, the synthesized polypyridazine, shows a predominantly uniform chemical structure with exceptional long-range order, allowing for structural characterization using vibrational spectroscopy and X-ray diffraction. The results demonstrate how thread-directing groups can be used for precise reaction pathway control and the formation of chemically precise nanothreads with a high degree of structural order.

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

Effect of high voltage electric field on structure and property of PEDOT:PSS film

Low electrical conductivity of PEDOT:PSS film is to some extent a limit for its wide application. To solve this problem, the high voltage electric field was used to improve the film’s electrical conductivity and its effects on the film’s structure and properties were investigated. The PEDOT:PSS film was prepared on quartz substrate with spin coating. Visible light transmittance of the prepared film was tested with UV–Visible spectroscopy and chemical structure was measured with Fourier transform Raman spectroscopy (FIRM). The surface morphology was characterized with AFM, and electrical conductivity was measured with Hall effects measurement. The results showed that with the increase of the electric field, the electrical conductivity of PEDOT:PSS film was boosted rapidly at first, and then improved slowly when the electric field was above 200 kV/m. The film’s electrical conductivity improved more than 17 times in total from 0.51 × 10{sup –3} up to 8.92 × 10{sup –3} S/m. However, the film’s visible light transmittance decreased only a little with the increase of the electric field, not more than 3%. In addition, despite little change in the chemical structure of the PEDOT:PSS film, its surface roughness increased significantly with the increase of the electric field intensity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Capture and Decomposition of the Nerve Agent Simulant, DMCP, Using the Zeolitic Imidazolate Framework (ZIF-8)

Understanding mechanisms of decontamination of chemical warfare agents (CWA) is an area of intense research aimed at developing new filtration materials to protect soldiers and civilians in case of state-sponsored or terrorist attack. In this study, we employed complementary structural, chemical, and dynamic probes and in situ data collection, to elucidate the complex chemistry, capture, and decomposition of the CWA simulant, dimethyl chlorophosphonate (DMCP). Our work reveals key details of the reactive adsorption of DMCP and demonstrates the versatility of zeolitic imidazolate framework (ZIF-8) as a plausible material for CWA capture and decomposition. Here, the in situ synchrotron-based powder X-ray diffraction (PXRD) and pair distribution function (PDF) studies, combined with Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), zinc K-edge X-ray absorption near edge structure (XANES), and Raman spectroscopies, showed that the unique structure, chemical state, and topology of ZIF-8 enable accessibility, adsorption, and hydrolysis of DMCP into the pores and revealed the importance of linker chemistry and Zn 2+ sites for nerve agent decomposition. DMCP decontamination and decomposition product(s) formation were observed by thermogravimetric analysis, FT-IR spectroscopy, and phosphorus (P) K-edge XANES studies. Differential PDF analysis indicated that the average structure of ZIF-8 (at the 30 Å scale) remains unchanged after DMCP dosing and provided information on the dynamics of interactions of DMCP with the ZIF-8 framework. Using in situ PXRD and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we showed that nearly 90% regeneration of the ZIF-8 structure and complete liberation of DMCP and decomposition products occur upon heating.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

OPERA models for predicting physicochemical properties and environmental fate endpoints

The collection of chemical structure information and associated experimental data for quantitative structure–activity/ property relationship (QSAR/QSPR) modeling is facilitated by an increasing number of public databases containing large amounts of useful data. However, the performance of QSAR models highly depends on the quality of the data and modeling methodology used. This study aims to develop robust QSAR/QSPR models for chemical properties of environmental interest that can be used for regulatory purposes. This study primarily uses data from the publicly available PHYSPROP database consisting of a set of 13 common physicochemical and environmental fate properties. These datasets have undergone extensive curation using an automated workflow to select only high-quality data, and the chemical structures were standardized prior to calculation of the molecular descriptors. The modeling procedure was developed based on the five Organization for Economic Cooperation and Development (OECD) principles for QSAR models. A weighted k-nearest neighbor approach was adopted using a minimum number of required descriptors calculated using PaDEL, an open-source software. The genetic algorithms selected only the most pertinent and mechanistically interpretable descriptors (2–15, with an average of 11 descriptors). The sizes of the modeled datasets varied from 150 chemicals for biodegradability half-life to 14,050 chemicals for logP, with an average of 3222 chemicals across all endpoints. The optimal models were built on randomly selected training sets (75%) and validated using fivefold cross-validation (CV) and test sets (25%). The CV Q2 of the models varied from 0.72 to 0.95, with an average of 0.86 and an R2 test value from 0.71 to 0.96, with an average of 0.82. Modeling and performance details are described in QSAR model reporting format and were validated by the European Commission’s Joint Research Center to be OECD compliant. All models are freely available as an open-source, command-line application called OPEn structure–activity/property Relationship App (OPERA). OPERA models were applied to more than 750,000 chemicals to produce freely available predicted data on the U.S. Environmental Protection Agency’s CompTox Chemistry Dashboard.

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

First-principles calculations of the electronic structure, phase transition and properties of ZrSiO4 polymorphs

First-principles periodic density functional theory (DFT) calculations have been performed to understand the electronic structure, chemical bonding, phase transition, and physical properties of the mineral zircon (in the chemical composition of ZrSiO4) and its high pressure phase reidite. Temperature effect on phase transition and thermal–mechanical properties such as heat capacity and bulk modulus have been studied by combining the equation of states obtained from DFT calculations with the quasi-harmonic Debye model to take into account the entropy contribution to free energy. Local density approximation (LDA) and generalized gradient approximation (GGA) DFT functionals have been systematically compared in predicting the structure and property of this material. It is found that the LDA functional provides a better description of the equilibrium structure and bulk modulus, while GGA predicts a transition pressure closer to experimental values. Both functionals correctly predict the relative stability of the two phases, with GGA giving slightly larger energy differences. The calculated band structures show that both zircon and reidite have indirect bandgaps and the reidite phase has a narrower bandgap than the zircon phase. The electronic density of states and atomic charges analyses show that bonding in the high-pressure reidite phase has a stronger covalent character.

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

Chemical Analysis of Fluorobenzenes via Multinuclear Detection in the Strong Heteronuclear J-Coupling Regime

Chemical analysis via nuclear magnetic resonance (NMR) spectroscopy using permanent magnets, rather than superconducting magnets, is a rapidly developing field. Performing the NMR measurement in the strong heteronuclear J-coupling regime has shown considerable promise for the chemical analysis of small molecules. Typically, the condition for the strong heteronuclear J-coupling regime is satisfied at µT magnetic field strengths and enables high resolution J-coupled spectra (JCS) to be acquired. However, the JCS response to systematic chemical structural changes has largely not been investigated. In this report, we investigate the JCS of C6H6−xFx (x = 0, 1, 2, …, 6) fluorobenzene compounds via simultaneous excitation and detection of 19F and 1H at 51.5 µT. The results demonstrate that JCS are quantitative, and the common NMR observables, including Larmor frequency, heteronuclear and homonuclear J-couplings, relative signs of the J-coupling, chemical shift, and relaxation, are all measurable and are differentiable between molecules at low magnetic fields. The results, corroborated by ab initio calculations, provide new insights into the impact of chemical structure and their corresponding spin systems on JCS. In several instances, the JCS provided more chemical information than traditional high field NMR, demonstrating that JCS can be used for robust chemical analysis.

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

Structure and magnetism in novel group IV element-based magnetic materials

The project is to investigate structure, magnetism and spin dependent states of novel group IV element-based magnetic thin films and heterostructures as a function of composition and epitaxial constraints. The materials systems of interest are Si-compatible epitaxial films and heterostructures of Si/Ge-based magnetic ternary alloys grown by non-equilibrium molecular beam epitaxy (MBE) techniques, specifically doped magnetic semiconductors (DMS) and half-metallic Heusler alloys. Systematic structural, chemical, magnetic, and electrical measurements are carried out, using x-ray microbeam techniques, magnetotunneling spectroscopy and microscopy, and magnetotransport. The work is aimed at elucidating the nature and interplay between structure, chemical order, magnetism, and spin-dependent states in these novel materials, at developing materials and techniques to realize and control fully spin polarized states, and at exploring fundamental processes that stabilize the epitaxial magnetic nanostructures and control the electronic and magnetic states in these complex materials. Combinatorial approach provides the means for the systematic studies, and the complex nature of the work necessitates this approach.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Direct Structural and Chemical Characterization of the Photolytic Intermediates of Methylcobalamin Using Time-Resolved X-ray Absorption Spectroscopy

Cobalt-carbon bond cleavage is crucial to most natural and synthetic applications of the cobalamin class of compounds, and here we present the first direct electronic and geometric structural characteristics of intermediates formed following photoexcitation of methylcobalamin (MeCbl) using time-resolved X-ray absorption spectroscopy (XAS). We catch transients corresponding to two intermediates, in the hundreds of picoseconds and a few microseconds. Highlights of the picosecond intermediate, which is reduced in comparison to the ground state, are elongation of the upper axial Co-C bond and relaxation of the corrin ring. This is not so with the recombining photocleaved products captured at a few microseconds, where the Co-C bond almost (yet not entirely) reverts to its ground state configuration and a substantially elongated lower axial Co-N Im bond is observed. In conclusion, the reduced cobalt site here confirms formation of methyl radical as the photoproduct.

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

Chemical and structural investigation of the paroxetine-human serotonin transporter complex

Antidepressants target the serotonin transporter (SERT) by inhibiting serotonin reuptake. Structural and biochemical studies aiming to understand binding of small-molecules to conformationally dynamic transporters like SERT often require thermostabilizing mutations and antibodies to stabilize a specific conformation, leading to questions about relationships of these structures to the bonafide conformation and inhibitor binding poses of wild-type transporter. To address these concerns, we determined the structures of ΔN72/ΔC13 and ts2-inactive SERT bound to paroxetine analogues using single-particle cryo-EM and x-ray crystallography, respectively. We synthesized enantiopure analogues of paroxetine containing either bromine or iodine instead of fluorine. We exploited the anomalous scattering of bromine and iodine to define the pose of these inhibitors and investigated inhibitor binding to Asn177 mutants of ts2-active SERT. These studies provide mutually consistent insights into how paroxetine and its analogues bind to the central substrate-binding site of SERT, stabilize the outward-open conformation, and inhibit serotonin transport.

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

Single nuclear spin detection and control in a van der Waals material

Optically active spin defects in solids are leading candidates for quantum sensing and quantum networking. Recently, single spin defects were discovered in hexagonal boron nitride (hBN), a layered van der Waals (vdW) material. Owing to its two-dimensional structure, hBN allows spin defects to be positioned closer to target samples than in three-dimensional crystals, making it ideal for atomic-scale quantum sensing, including nuclear magnetic resonance (NMR) of single molecules. However, the chemical structures of these defects remain unknown and detecting a single nuclear spin with a hBN spin defect has been elusive. Here we report the creation of single spin defects in hBN using 13 C ion implantation and the identification of three distinct defect types based on hyperfine interactions. We observed both S = 1/2 and S = 1 spin states within a single hBN spin defect. We demonstrated atomic-scale NMR and coherent control of individual nuclear spins in a vdW material, with a π-gate fidelity up to 99.75% at room temperature. By comparing experimental results with density functional theory (DFT) calculations, we propose chemical structures for these spin defects. Our work advances the understanding of single spin defects in hBN and provides a pathway to enhance quantum sensing using hBN spin defects with nuclear spins as quantum memories.

Quantum metrology↗
DOE OSTI2016

Study of the structure and chemical bonding of crystalline Ge{sub 4}Sb{sub 2}Te{sub 7} using first principle calculations

The atomic arrangements and chemical bonding of stable Ge{sub 4}Sb{sub 2}Te{sub 7} (GeTe rich), a phase-change material, have been investigated by means of ab initio total energy calculations. To study the atomic arrangement, GeTe block is considered into -TeSbTeSbTe- block and -Te-Te- layer in the stacking I and II respectively. The stacking I is energetically more stable than the stacking II. The reason for more stability of the stacking I has been explained. The chemical bonding has been studied with the electronic charge density distribution around the atomic bonds. The quantity of electronic charge loosed or gained by atoms has been calculated using the Bader charge analysis. The metallic character has been studied using band structures calculations. The band gap for the stacking I and II is 0.463 and 0.219 eV respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Polymer useful for an ion exchange membrane

The present invention provides for a polymer formed by reacting a first reactant polymer, or a mixture of first reactant polymers comprising different chemical structures, comprising a substituent comprising two or more nitrogen atoms (or a functional group/sidechain comprising a two or more nitrogen atoms) with a second reactant polymer, or a mixture of second reactant polymers comprising different chemical structures, comprising a halogen substituent (or a functional group/sidechain comprising a halogen).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Structural and Chemical Evolution of Highly Fluorinated Li‐Rich Disordered Rocksalt Oxyfluorides as a Function of Temperature

Abstract Li‐rich disordered rocksalt (DRS) oxyfluorides have emerged as promising high‐energy cathode materials for lithium‐ion batteries. While a high level of fluorination in DRS materials offers performance advantages, it can only be achieved via mechanochemical synthesis, which poses challenges of reproducibility and scalability. The definition of relationships between fluorination and structural stability is required to devise alternative methods that overcome these challenges. In this study, the thermal evolution of three highly fluorinated phases, Li 2 TMO 2 F (TM = Mn, Co, and Ni), is investigated in an inert atmosphere. Diffraction and spectroscopic techniques are utilized to examine their electronic and chemical states up until conditions of decomposition. The analysis reveals that the materials phase‐separate above 400 °C, at most. It is also observed that heat‐treated DRS materials exhibit intricate changes in the local coordination of the metals, including their spin, and ordering compared to the pristine states. The changes upon annealing are accompanied by a modulation of the voltage profile, including reduced hysteresis, when used as electrodes. These results provide an in‐depth understanding of the fundamental crystal chemistry of DRS oxyfluorides in view of their promising role as the next generation of Li‐ion cathodes.

25 ENERGY STORAGE↗
DOE OSTI2014

Breaking the limits of structural and mechanical imaging of the heterogeneous structure of coal macerals

The correlation between local mechanical (elasto-plastic) and structural (composition) properties of coal presents significant fundamental and practical interest for coal processing and the development of rheological models of coal to coke transformations and for advancing novel approaches. Here, we explore the relationship between the local structural, chemical composition and mechanical properties of coal using a combination of confocal micro-Raman imaging and band excitation atomic force acoustic microscopy (BE-AFAM) for a bituminous coal. This allows high resolution imaging (10s of nm) of mechanical properties of the heterogeneous (banded) architecture of coal and correlating them to the optical gap, average crystallite size, the bond-bending disorder of sp2 aromatic double bonds and the defect density. This methodology hence allows the structural and mechanical properties of coal components (lithotypes, microlithotypes, and macerals) to be understood, and related to local chemical structure, potentially allowing for knowledge-based modelling and optimization of coal utilization processes.

36 MATERIALS SCIENCE↗
NASA NTRS2008

Non-Destructive Evaluation of Materials via Ultraviolet Spectroscopy

A document discusses the use of ultraviolet spectroscopy and imaging for the non-destructive evaluation of the degree of cure, aging, and other properties of resin-based composite materials. This method can be used in air, and is portable for field use. This method operates in reflectance, absorbance, and luminescence modes. The ultraviolet source is used to illuminate a composite surface of interest. In reflectance mode, the reflected response is acquired via the imaging system or via the spectrometer. The spectra are analyzed for organic compounds (conjugated organics) and inorganic compounds (semiconducting band-edge states; luminescing defect states such as silicates, used as adhesives for composite aerospace applications; and metal oxides commonly used as thermal coating paints on a wide range of spacecraft). The spectra are compared with a database for variation in conjugation, substitution, or length of molecule (in the case of organics) or band edge position (in the case of inorganics). This approach is useful in the understanding of material quality. It lacks the precision in defining the exact chemical structure that is found in other materials analysis techniques, but it is advantageous over methods such as nuclear magnetic resonance, infrared spectroscopy, and chromatography in that it can be used in the field to assess significant changes in chemical structure that may be linked to concerns associated with weaknesses or variations in structural integrity, without disassembly of or destruction to the structure of interest.

Pugel, Betsy↗
DOE OSTI2026

Unveiling the electronic structure and chemical bonding of the deprotonated cisplatin anion [(NH 3 )(NH 2 )PtCl 2 ] − via low-temperature photoelectron spectroscopy and theoretical calculations

The dehydrogenated cisplatin anion, [(NH 3 )(NH 2 )PtCl 2 ] − , was investigated via low-temperature photoelectron spectroscopy and theoretical calculations. Seven and four spectral peaks are respectively resolved at 193 and 266 nm, yielding rich electronic structure information for both the anion and neutral. From the threshold and maximum of the lowest electron binding energy band, the experimental adiabatic (ADE) and vertical detachment energies (VDE) are determined to be 3.3 ± 0.1 and 3.525 ± 0.025 eV, respectively. Theoretical calculations indicate the dominant isomer adopting a cis-geometry, in which the platinum center is coplanar with two chlorine and two nitrogen ligands. The calculated VDE of 3.54 eV based on this structure agrees well with the experimental value. Charge analyses reveal that the excess electron in the anion is primarily localized on the Pt and Cl atoms. A suite of theoretical analysis tools was employed to elucidate the bonding characteristics and interaction strength between Pt and its ligands.

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

Identifying Atomic Scale Structure in Undoped/Doped Semicrystalline P3HT Using Inelastic Neutron Scattering

The greatest advantage of organic materials is the ability to synthetically tune desired properties. However, structural heterogeneity often obfuscates the relationship between chemical structure and functional properties. Inelastic neutron scattering (INS) is sensitive to both local structure and chemical environment and provides atomic level details that cannot be obtained through other spectroscopic or diffraction methods. INS data are composed of a density of vibrational states with no selection rules, which means that every structural configuration is equally weighted in the spectrum. This allows the INS spectrum to be quantitatively decomposed into different structural motifs. Here in this paper we present INS measurements of the semiconducting polymer P3HT doped with F4TCNQ supported by density functional theory calculations to identify two dominant families of undoped crystalline structures and one dominant doped structural motif, in spite of considerable heterogeneity. The differences between the undoped and doped structures indicate that P3HT side chains flatten upon doping.

36 MATERIALS SCIENCE↗