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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Effect of Local Structural Distortions on Antiferroelectric–Ferroelectric Phase Transition in Dilute Solid Solutions of K x Na 1– x NbO 3

The fundamental principles that govern antiferroelectric (AFE)–ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as K x Na 1– x NbO 3 ( x ≤ 0.02). Here, based on detailed structural analysis from neutron total scattering experiments, we provide insights about how the relative local distortions around the A- and B-sites of the ABO 3 perovskite structure affect the AFE/FE order of the average crystallographic phases in K x Na 1– x NbO 3 . Specifically, we show that a higher (lower) ratio of B-site-centered distortions over A-site-centered distortions drives transition toward a long-range FE (AFE) phase, which is based on a competition between the long-range polarizing field of the Nb–O dipoles and the disordering effect of local distortions around the A-site. Our study provides a predictive tool for designing complex solid-solution perovskites with tunable (anti)ferroelectric polarization properties, which can be of interest for various energy-related applications such as high-density energy storage and solid-state cooling.

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

Oxygen Defect Configurations in Single-Phase UO 2.15

Hyperstoichiometric UO 2.15 was characterized by neutron total scattering at high temperature in the single-phase UO 2+x region of the U/O phase diagram. The diffraction data confirmed a single-phase fluorite structure at high temperature. Analysis of the short-range data showed that the same structural model does not fit the pair distribution functions well. Instead, structural models containing specific configurations of oxygen defect clusters best represent the local atomic arrangement. In conclusion, prevalent defect clusters previously proposed were fit to the experimental data, and moderately distorted oxygen cuboctahedra hypothesized by recent molecular dynamics simulations fit the data most accurately.

neutron pair-distribution function analysis↗
DOE OSTI2016

Paracrystalline Disorder from Phosphate Ion Orientation and Substitution in Synthetic Bone Mineral

Hydroxyapatite is an inorganic mineral closely resembling the mineral phase in bone. However, as a biological mineral, it is highly disordered, and its composition and atomistic structure remain poorly understood. Here, synchrotron X-ray total scattering and pair distribution function analysis methods provide insight into the nature of atomistic disorder in a synthetic bone mineral analogue, chemically substituted hydroxyapatite. By varying the effective hydrolysis rate and/or carbonate concentration during growth of the mineral, compounds with varied degrees of paracrystallinity are prepared. From advanced simulations constrained by the experimental pair distribution function and density functional theory, the paracrystalline disorder prevalent in these materials appears to result from accommodation of carbonate in the lattice through random displacement of the phosphate groups. Though many substitution modalities are likely to occur in concert, the most predominant substitution places carbonate into the mirror plane of an ideal phosphate site. Here, by understanding the mineralogical imperfections of a biologically analogous hydroxyapatite is important not only to potential bone grafting applications but also to biological mineralization processes themselves.

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

Structure and Phase Transformation in the Giant Magnetostriction Laves-Phase SmFe 2

As one class of the most important intermetallic compounds, the binary Laves-phase is well-known for their abundant magnetic properties. Samarium-iron alloy system, SmFe 2 , is a prototypical Laves compound that shows strong negative magnetostriction but relatively weak magnetocrystalline anisotropy. SmFe 2 has been identified as a cubic Fd$ \overline{3}\ $m structure at room temperature, however, the cubic symmetry does not match the spontaneous magnetization along the [111] cubic direction. Here we studied the crystal structure of SmFe 2 by high-resolution synchrotron X-ray powder diffraction and X-ray total scattering methods. SmFe 2 is found to adopt a centrosymmetric trigonal R$ \overline{3}\ $m structure at room temperature, which transforms to an orthorhombic Imma structure at 200 K. This transition is in agreement with the changes of easy magnetization direction from [111] cubic to [110] cubic direction, and is further evidenced by the inflexion of thermal expansion behavior, the sharp decline of the magnetic susceptibility in the FC-ZFC curve, and the anomaly in the specific heat capacity measurement. Lastly, the revised structure and phase transformation of SmFe 2 could be useful to understand the magnetostriction and related physical properties of other RM 2 -type pseudo-cubic Laves-phase intermetallic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Low-Frequency Phonon Driven Negative Thermal Expansion in Cubic GaFe(CN) 6 Prussian Blue Analogues

Here, the understanding of the negative thermal expansion (NTE) mechanism is vital not only for the development of new NTE compounds but also for effectively controlling thermal expansion. Here, we report an interesting isotropic NTE property in cubic GaFe(CN) 6 Prussian blue analogues (α l = –3.95 × 10 –6 K –1 , 100–475 K), which is a new example to understand the complex NTE mechanism. A combined study of synchrotron X-ray diffraction, X-ray total scattering, X-ray absorption fine structure, neutron powder diffraction, and density functional theory calculations shows that the NTE of GaFe(CN)6 originates from the low-frequency phonons (< ~100 cm –1 ), which are directly related to the transverse vibrations of the atomic –Ga–N≡C–Fe– chains. Both the Ga–N and Fe–C chemical bonds are much softer to bend than to stretch. The direct evidence that transverse vibrational contribution to the NTE of GaFe(CN) 6 is dominated by N, instead of C atoms, is illustrated. It is interesting to find that the polyhedra of GaFe(CN) 6 are not rigid, which is a starting assumption in some models describing the NTE properties of other systems. The NTE mechanism can be vividly described by the “guitar-string” effect, which would be the common feature for the NTE property of many open-framework functional materials, such as Prussian blue analogues, oxides, cyanides, metal–organic frameworks, and zeolites.

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

Structural, Chemical, Electrical, and Thermal Properties of n -Type NbFeSb

Here, we report on the structural, chemical, electrical, and thermal properties of n -type polycrystalline NbFeSb synthesized by induction melting of the elements. Although several studies on p -type conduction of this half-Heusler composition have recently been reported, including reports of relatively high thermoelectric properties, very little has been reported on the transport properties of n-type compositions. We combine transport property investigations together with short- and long-range structural data obtained by Mössbauer spectroscopy of iron-57 and antimony-121 and by neutron total scattering, as well as first-principles calculations. In our investigation, we show that n -type conduction can occur from antiphase boundaries in this material. This work is intended to provide a greater understanding of the fundamental properties of NbFeSb as this material continues to be of interest for potential thermoelectric applications.

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

Structure of Sulfuric Acid Solutions Using Pair Distribution Function Analysis

Solvation and mesoscale ordering of sulfuric acid and other strong acid solutions leads to suppressed freezing points and strong rheological changes with varying concentration. While the solid-state structures are well-understood, studies focused on the evolving solvation structure in the solution phase have probed a limited concentration range (~1–6 M). This study applies a total scattering approach in both the wide-angle X-ray scattering (WAXS) and pair distribution function (PDF) regimes to elucidate the evolving solvation structure over its full range of acid concentration (0–18 M). The emergence of a prepeak in the WAXS regime at intermediate concentrations indicates a transition from noninteracting sulfate molecules in the dilute limit to sterically limited sulfates at concentrations near its deep eutectic point. Fits to the PDF data quantify this trend, showing a transition from octahedrally hydrated sulfates up to 6–7 M concentrations, followed by gradual dehydration, and eventually reaching a solution structure similar to that of water-in-salt electrolyte systems at high acid concentrations.

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

Operando Studies Reveal Structural Evolution with Electrochemical Cycling in Li–CoS 2

The desire for high energy density alternatives to Li-ion batteries has led to great interest in energy storage materials not inherently constrained by the capacity limits of standard intercalation electrode materials currently employed in commercial devices. Among the alternatives under consideration are electrode materials with theoretical capacities many times greater than intercalation electrodes, including those that store charge through so-called conversion reactions. However, the vast structural changes that enable the high theoretical capacity of conversion systems contribute to issues of poor efficiency and short cycle life. To better understand the cycling issues in conversion systems, we study the local structure evolution of the cathode active material in LiCoS 2 cells. Being metallic, and potentially being capable of redox on both the anion and cation, we would expect CoS 2 to be a promising cathode material. Through combined ex situ X-ray absorption near-edge spectroscopy and pair distribution function analysis from operando X-ray total scattering, we describe the reactions that take place over the first 1.5 cycles. In doing so, we identify the irreversible formation of a Co 9 S 8 -like local structure with significantly limited electrochemical activity as the primary source of capacity fade. The methods employed here and the insights that emerge inform the rational design of conversion systems for electrochemical energy storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Measuring the Degree of Crystallinity in Semicrystalline Regioregular Poly(3-hexylthiophene)

By using a combination of wide-angle X-ray diffraction (WAXD), mass density, and 13 C solid-state nuclear magnetic resonance (NMR) measurements, a quantification of the absolute degree of crystallinity in regioregular poly(3-hexylthiophene) (rr-P3HT) is presented. A regiorandom P3HT (rra-P3HT), lacking long-range order, was used to separate the crystalline contribution from the total scattering in WAXD, thus yielding degrees of crystallinity in the range of 47–56% at room temperature for three different rr-P3HTs. For the same rr-P3HT with identical processing history, NMR yields degrees of crystallinity that are consistently ~10% greater than that obtained by WAXD, which can only be explained by ordered chain segments in the amorphous phase. NMR results also suggest that rra-P3HT contains weakly ordered chain segments, which likely contribute to an underestimation of degree of crystallinity when determined from mass density measurements, if rra-P3HT is used to approximate a fully amorphous P3HT. The results shown in this study provide direct proof of three different types of P3HT chain segments: crystallites (i.e., long-range ordered chain packing), amorphous phase (i.e., disordered chain packing), and short-range ordered chain packing embedded in the amorphous phase. Here, the presence of the short-range ordered chain packing is particularly important when correlating the morphology to macroscopic charge transport properties in P3HT-based devices. In general, those locally ordered chain segments, though not constituting a distinct phase, are believed to be of critical importance in determining the transport characteristics of conjugated semiconducting polymers with or without a distinct crystalline phase present.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Crystal Structure of Colloidally Prepared Metastable Ag 2 Se Nanocrystals

Structural polymorphism is known for many bulk materials; however, on the nanoscale metastable polymorphs tend to form more readily than in the bulk, and with more structural variety. One such metastable polymorph observed for colloidal Ag 2 Se nanocrystals has traditionally been referred to as the “tetragonal” phase. While there are reports on the chemistry and properties of this metastable polymorph, its crystal structure, and therefore electronic structure, has yet to be determined. We report that an anti-PbCl 2 -like structure type (space group P2 1 /n) more accurately describes the powder X-ray diffraction and X-ray total scattering patterns of colloidal Ag 2 Se nanocrystals prepared by several different methods. Density functional theory (DFT) calculations indicate that this anti-PbCl 2 -like Ag 2 Se polymorph is a dynamically stable, narrow-band-gap semiconductor. Here, the anti-PbCl 2 -like structure of Ag 2 Se is a low-lying metastable polymorph at 5–25 meV/atom above the ground state, depending on the exchange-correlation functional used.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Electrochemical and Chemical Reactivities of Titanium Oxide-Based Materials with a Chloroaluminate Ionic Liquid Electrolyte for Aluminum Batteries

Here, by selecting three different types of electrode materials, we intended to better understand the Al 3+ intercalation chemistry of titanium oxide-based frameworks with an acidic chloroaluminate electrolyte. In agreement with previous reports, we confirmed that the native interstitial sites of anatase TiO 2 are less prone to accommodate Al 3 + than Li + or Na + ions, while introducing cationic vacancies largely increases the electrochemical storage capacity. Upon the first cycle, the highest reversible capacity, up to 277 mAh/g, was obtained for a hydrated layered structure featuring cationic vacancies. Total scattering data showed that the insertion of Al 3+ ions induced a strong distortion of the framework. In addition, combined 27 Al MAS NMR and DFT calculations revealed that in oxy-hydroxylated vacant sites, the coordination mode of Al 3+ ions depends on the arrangement of anions around vacancies inducing the occurrence of 4-, 5-, and 6-fold coordination modes. Further cycling experiments revealed a progressive capacity fading for all electrode materials. Using cyclic voltammetry on the used electrolyte, we evidenced that a partial dissolution has occurred, which is more pronounced for the layered hydrate compound, and that solubilized species are electrochemically active, giving rise to specific signatures in both CVs and galvanostatic experiments. Raman spectroscopy enabled us to characterize these species, which are derived from the Ti-Cl system. The solubilized species, however, eventually precipitated, as shown by a purple deposit observed on the separator and tentatively assigned to TiCl 3 , known to be insoluble in this medium. By providing further information on the Al 3+ intercalation chemistry and a better understanding of the electrochemical and chemical reactivities of electrode materials, this work will enable progress to be made in the development of aluminum-ion batteries.

Al3+-ion insertion chemistry↗
DOE OSTI2017

Hydrothermal Preparation, Crystal Chemistry, and Redox Properties of Iron Muscovite Clay

The development of functional materials based on Earthabundant, environmentally benign compositions is critical for ensuring their commercial viability and sustainable production. In this paper we present an investigation into the crystal chemistry and electrochemical properties of the muscovite clay KFe 2.75 Si 3.25 O 10 (OH) 2 . We first report a low-temperature hydrothermal reaction that allows for a significant degree of control over sample crystallinity, particle morphology, and cation distribution through the lattice. A complex sequence of stacking faults is identified and characterized using a combination of M&ouml;ssbauer spectroscopy and total scattering neutron experiments. We then show the existence of a reversible electrochemical process using galvanostatic cycling with complementary cyclic voltammetry suggesting that the redox activity occurs primarily on the surface of the particles. We conclude by determining that the ability to (de)intercalate Li ions from the material is hindered by the strong negative charge on the transition metal silicate layers, which prevents the displacement of the interlayer K ions. This work calls attention to a hugely Earth-abundant family of minerals that possesses useful electrochemical properties that warrant further exploration.

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

Morphology and Dynamics in Hydroxide-Conducting Polysulfones

In alkaline zinc–manganese dioxide batteries, there is a need for selective polymeric separators that have good hydroxide ion conductivity but that prevent the transport of zincate (Zn(OH) 4 ) 2- . Here we investigate the nanoscale structure and hydroxide transport in two cationic polysulfones that are promising for these separators. We present the synthesis and characterization for a tetraethylammonium-functionalized polysulfone (TEA-PSU) and compare it to our previous work on an N-butylimidazolium-functionalized polysulfone (NBI-PSU). We perform atomistic molecular dynamics (MD) simulations of both polymers at experimentally relevant water contents. The MD simulations show that both polymers develop well phase separated nanoscale water domains that percolate through the polymer. Calculation of the total scattering intensity from the MD simulations reveal weak or nonexistent ionomer peaks at low wave vectors. The lack of an ionomer peak is due to a loss of contrast in the scattering. The small water domains in both polymers, with median diameters on the order of 0.5–0.7 nm, lead to hydroxide and water diffusion constants that are 1–2 orders of magnitude smaller than their values in bulk water. This confinement lowers the conductivity but also may explain the strong exclusion of zincate from the PSU membranes seen experimentally.

25 ENERGY STORAGE↗
DOE OSTI2021

Water or Anion? Uncovering the Zn 2+ Solvation Environment in Mixed Zn(TFSI) 2 and LiTFSI Water-in-Salt Electrolytes

Applications of aqueous zinc batteries for grid-scale energy storage are limited by their poor reversibility and the competing water splitting reaction. The recent invention of a water-in-salt (WIS) electrolyte concept provides a new route enabling a stable and highly reversible aqueous zinc battery chemistry. In the present work, a mixed zinc bis(trifluoromethane sulfonyl)imide (Zn(TFSI) 2 ) and LiTFSI WIS electrolyte was studied using X-ray total scattering, X-ray absorption, and Fourier transform infrared spectroscopy in conjunction with classical molecular dynamics simulations. It was found that, in the highly concentrated WIS electrolyte consisting of 1 m Zn(TFSI) 2 and 20 m LiTFSI, Zn 2+ cations are mainly solvated by six waters in their first solvation shell, while the TFSI – anions are completely excluded. This ion solvation picture is fundamentally different from the previous understandings. The results suggest that additional studies are needed to fully understand the unusual stability and reversibility of zinc-WIS electrolyte-based batteries.

25 ENERGY STORAGE↗
DOE OSTI2016

High Capacity of Hard Carbon Anode in Na-Ion Batteries Unlocked by PO x Doping

The capacity of hard carbon anodes in Na-ion batteries 2.5 rarely reaches values beyond 300 mAh/g. We report that doping POx into local structures of hard carbon increases its reversible capacity from 283 to 359 mAh/g. We confirm that the doped POx is redox inactive by X-ray adsorption near edge structure measurements, thus not contributing to the higher capacity. We observe two significant changes of hard carbon's local structures caused by doping. First, the (002) d-spacing inside the turbostratic nanodomains is increased, revealed by both laboratory and synchrotron X-ray diffraction. Second, doping turns turbostratic nanodomains more defective along ab planes, indicated by neutron total scattering and the associated pair distribution function studies. The local structural changes of hard carbon are correlated to the higher capacity, where both the plateau and slope regions in the potential profiles are enhanced. Our study demonstrates that Na-ion storage in hard carbon heavily depends on carbon local structures, where such structures, despite being disordered, can be tuned toward unusually high capacities.

25 ENERGY STORAGE↗
DOE OSTI2023

Synthesis, Structure, and Photophysical Properties of Platinum Compounds with Thiophene-Derived Cyclohexyl Diimine Ligands

Platinum(II) and platinum(IV) compounds were prepared by the stereoselective and regioselective reactions of thiophene-derived cyclohexyl diimine C^N^N-ligands with [Pt 2 Me 4 (μ-SMe 2 ) 2 ]. Newly synthesized ligands were characterized by NMR spectroscopy and elemental analysis, and Pt(II)/Pt(IV) compounds were characterized by NMR spectroscopy, elemental analysis, high-resolution mass spectrometry, and single-crystal X-ray diffraction. UV–vis absorbance and photoluminescence measurements were performed on newly synthesized complexes, as well as structurally related Pt(II)/Pt(IV) compounds with benzene-derived cyclohexyl diimine ligands, in dichloromethane solution, as solids, and as 5% by weight PMMA-doped films. DFT and TD-DFT calculations were performed, and the results were compared with the observed spectroscopic properties of the newly synthesized complexes. X-ray total scattering measurements and real space pair distribution function analysis were performed on the synthesized complexes to examine the local- and intermediate-range atomic structures of the emissive solid states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Consequences of Optimal Bond Valence on Structural Rigidity and Improved Luminescence Properties in Sr x Ba 2-x SiO 4 :Eu 2+ Orthosilicate Phosphors

The orthosilicate phosphors Sr x Ba 2–x SiO 4 :Eu 2+ have now been known for over four decades and have found extensive recent use in solid-state white lighting. It is well-recognized in the literature and in practice that intermediate compositions in the solid-solutions between the orthosilicates Sr 2 SiO 4 and Ba 2 SiO 4 yield the best phosphor hosts when the thermal stability of luminescence is considered. We employ a combination of synchrotron X-ray diffraction, total scattering measurements, density functional theory calculations, and low-temperature heat capacity measurements, in conjunction with detailed temperature- and time-resolved studies of luminescence properties to understand the origins of the improved luminescence properties. We observe that in the intermediate compositions, the two cation sites in the crystal structure are optimally bonded as determined from bond valence sum calculations. Optimal bonding results in a more rigid lattice, as established by the intermediate compositions possessing the highest Debye temperature, which are determined experimentally from low-temperature heat capacity measurements. Greater rigidity in turn results in the highest luminescence efficiency for intermediate compositions at elevated temperatures.

Denault, Kristin A.↗