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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Electron density distribution in BaPb{sub 1-x}Sb{sub x}O{sub 3} superconducting oxides studied by double nuclear magnetic resonance methods

The effect of charge disorder on the formation of an inhomogeneous state of the electron system in the conduction band in BaPb{sub 1-x}Sb{sub x}O{sub 3} superconducting oxides is investigated experimentally by NMR methods. The NMR spectra of {sup 17}O are measured systematically, and the contributions from {sup 17}O atoms with different cation nearest surroundings are identified. It is found that microscopic regions with an elevated spin density of charge carriers are formed within two coordination spheres near antimony ions. Nuclei of the superconducting phase of the oxide (regions with an elevated antimony concentration) microscopically distributed over the sample are detected in compounds with x = 0.25 and 0.33. Experiments in which a double resonance signal of the spin echo of {sup 17}O-{sup 207}Pb and {sup 17}O-{sup 121}Sb are measured in the metal phase of BaPb{sub 1-x}Sb{sub x}O{sub 3} oxides are carried out for the first time. The constants of indirect heteronuclear spin-spin {sup 17}O-{sup 207}Pb interaction are determined as functions of the local Knight shift {sub 207}Ks. The estimates of the constants of the indirect interaction between the nuclei of the nearest neighbors (O-Pb and Pb-Pb atoms) and analysis of evolution of the NMR spectra of {sup 17}O upon a change in the antimony concentration are convincing evidence in favor of the development of a microscopically inhomogeneous state of the electron system in the metal phase of BaPb{sub 1-x}Sb{sub x}O{sub 3} oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Both Free and Trapped Carriers Contribute to Photocurrent of Sb 2 Se 3 Solar Cells

Polycrystalline semiconductor films, such as methylammonium lead iodide, cadmium telluride, copper-indium-gallium selenide, etc., are being intensively studied due to their great potential for highly efficient and cost-effective solar cells. Among them, polycrystalline antimony chalcogenide films are also promising for photovoltaic applications because they are nontoxic, stable, flexible, and have a suitable bandgap. Considerable effort has already been devoted to improving the power conversion efficiency of antimony chalcogenide solar cells, but their efficiency still lingers below 10% due in part to scarce fundamental optoelectronic studies that help guide their development. Here, we use a combination of time-resolved terahertz and transient absorption spectroscopies to interrogate the optoelectronic behavior of antimony selenide thin films. By combining these two techniques we are able to monitor both free and trapped carrier dynamics and then evaluate their respective diffusion lengths. Our results indicate that trapped carriers remain mobile and can reach charge collecting interfaces prior to recombination, and therefore, both free and trapped carriers can contribute to the photocurrent of antimony selenide solar cells.

14 SOLAR ENERGY↗
DOE OSTI2016

Tracking Sodium-Antimonide Phase Transformations in Sodium-Ion Anodes: Insights from Operando Pair Distribution Function Analysis and Solid-State NMR Spectroscopy

Operando pair distribution function (PDF) analysis and ex situ Na-23 magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy are used to gain insight into the alloying mechanism of high-capacity antimony anodes for sodium-ion batteries. Subtraction of the PDF of crystalline NaxSb phases from the total PDF, an approach constrained by chemical phase information gained from Na-23 ssNMR in reference to relevant model compounds, identifies two previously uncharacterized intermediate species formed electro-chemically; a-Na3-xSb (x approximate to 0.4-0.5), a structure locally similar to crystalline Na3Sb (c-Na3Sb) but with significant numbers of sodium vacancies and a limited correlation length, and a-Na1.7Sb, a highly amorphous structure featuring some Sb-Sb bonding. The first sodiation breaks down the crystalline antimony to form first a-Na3-xSb and, finally, crystalline Na3Sb. Desodiation results in the formation of an electrode formed of a composite of crystalline and amorphous antimony networks. We link the different reactivity of these networks to a series of sequential sodiation reactions manifesting as a cascade of processes observed in the electrochemical profile of subsequent cycles. The amorphofis network reacts at higher voltages reforming a-Na1.7Sb, then a-Na3-xSb, whereas lower potentials are required for the sodiation of crystalline antimony, which reacts to form a-Na3-xSb without the formation of a-Na3-xSb. a-Na3-xSb is converted to crystalline Na3Sb at the end of the second discharge. We find no evidence of formation of NaSb. Variable temperature Na-23 NMR experiments reveal significant sodium mobility within c-Na3Sb; this is a possible contributing factor to the excellent rate performance of Sb anodes.

Allan, Phoebe K.↗
DOE OSTI2020

Spontaneous and reversible hollowing of alloy anode nanocrystals for stable battery cycling

High-capacity alloy anode materials for Li-ion batteries have long been held back by limited cyclability caused by the large volume changes during lithium insertion and removal. Hollow and yolk-shell nanostructures have been used to increase the cycling stability by providing an inner void space to accommodate volume changes and a mechanically and dimensionally stable outer surface. These materials, however, require complex synthesis procedures. Here, using in situ transmission electron microscopy, we show that sufficiently small antimony nanocrystals spontaneously form uniform voids on the removal of lithium, which are then reversibly filled and vacated during cycling. This behaviour is found to arise from a resilient native oxide layer that allows for an initial expansion during lithiation but mechanically prevents shrinkage as antimony forms voids during delithiation. In this work, we developed a chemomechanical model that explains these observations, and we demonstrate that this behaviour is size dependent. Thus, antimony naturally evolves to form optimal nanostructures for alloy anodes, as we show through electrochemical experiments in a half-cell configuration in which 15-nm antimony nanocrystals have a consistently higher Coulombic efficiency than larger nanoparticles.

25 ENERGY STORAGE↗
DOE OSTI2017

Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing

Operation speed is a key challenge in phase-change random-access memory (PCRAM) technology, especially for achieving subnanosecond high-speed cache memory. Commercialized PCRAM products are limited by the tens of nanoseconds writing speed, originating from the stochastic crystal nucleation during the crystallization of amorphous germanium antimony telluride (Ge 2 Sb 2 Te 5 ). Here, we demonstrate an alloying strategy to speed up the crystallization kinetics. The scandium antimony telluride (Sc 0.2 Sb 2 Te 3 ) compound that we designed allows a writing speed of only 700 picoseconds without preprogramming in a large conventional PCRAM device. This ultrafast crystallization stems from the reduced stochasticity of nucleation through geometrically matched and robust scandium telluride (ScTe) chemical bonds that stabilize crystal precursors in the amorphous state. Controlling nucleation through alloy design paves the way for the development of cache-type PCRAM technology to boost the working efficiency of computing systems.

Science & Technology - Other Topics↗
NASA NTRS1982

Venus: Halide cloud condensation and volatile element inventories

Several Venus cloud condensates, including A12C16 as well as halides, oxides and sulfides of arsenic and antimony, are assessed for their thermodynamic and geochemical plausibility. Aluminum chloride can confidently be ruled out, and condensation of arsenic sulfides on the surface will cause arsenic compounds to be too rare to produce the observed clouds. Antimony may conceivably be sufficiently volatile, but the expected molecular form is gaseous SbS, not the chloride. Arsenic and antimony compounds in the atmosphere will be regulated at very low levels by sulfide precipitation, irrespective of the planetary inventory of As and Sb. Thus the arguments for a volatile-deficient origin for Venus based on the depletion of water and mercury (relative to Earth) cannot be tested by a search for atmospheric arsenic or antimony.

Lewis, J. S.↗
DOE OSTI2019

Development of the Physicochemical Properties of the GaSb(100) Surface in Ammonium Sulfide Solutions

Various conditions of passivation of the GaSb(100) surface by ammonium sulfide ((NH{sub 4}){sub 2}S) solutions depending on the solution concentration, solvent, and treatment time are investigated by X-ray photoelectron spectroscopy and atomic-force microscopy. It is shown that treatment of the GaSb(100) surface by any (NH{sub 4}){sub 2}S solution leads to removal of the native oxide layer from the semiconductor surface and the formation of a passivating layer consisting of various gallium and antimony sulfides and oxides. The surface with the lowest roughness (RMS = 0.85 nm) is formed after semiconductor treatment with 4% aqueous ammonium sulfide solution for 30 min. Herewith, the atomic concentration ratio Ga/Sb at the surface is ~2. It is also found that aqueous ammonium sulfide solutions do not react with elemental antimony incorporated into the native-oxide layer. The latter causes a leakage current and Fermi-level pinning at the GaSb(100) surface. However, a 4% (NH{sub 4}){sub 2}S solution in isopropanol removes elemental antimony almost completely; herewith, the semiconductor surface remains stoichiometric if a treatment duration is up to 13 min.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of isovalent substitution on microstructure and phase transition of LaNb{sub 1−x}M{sub x}O{sub 4} (M=Sb, V or Ta; x=0.05–0.3)

LaNb{sub 1−x}M{sub x}O{sub 4} oxides with pentavalent elements of different ionic sizes (M=Sb, Ta and V, x=0.05–0.3) were synthesized by the solid state reaction method. Special interest was devoted to the antimony substituted lanthanum niobate which is a new material in this group. Rietveld analysis of the X-ray diffraction patterns was used to determine the influence of the material composition on unit cell parameters. On the basis of dilatometric measurements phase transition temperatures and thermal expansion coefficients of the studied materials were determined. It was shown that with increasing concentration of Sb the phase transition temperature decreases. Thermal expansion coefficient of the antimony substituted samples above the transition temperature is in the range from 8.1 to 9.1×10{sup −6} 1/K, whereas below the transition temperature the TEC value is between 14 and 17.3×10{sup −6} 1/K. Influence of Ta, V and Sb substitutions on the microstructure and grain size was studied. - Graphical abstract: Substitution of niobium by other pentavalent elements in LaNbO{sub 4} leads to change in phase transition temperature. In case of Sb substituent a shift of phase transition into the lower temperature region is observed. LaNb{sub 0.7}Sb{sub 0.3}O{sub 4} substitution allows to achieve material with tetragonal crystal structure at room temperature and no phase transition up to 1000 °C. - Highlights: • Antimony doped lanthanum niobate was successfully synthesized by solid state synthesis method. • The structural properties have been investigated by XRD and SEM. • The influence of doping on phase transition temperature has been studied.

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

Study of various Sb{sub 2}S{sub 3} nanostructures synthesized by simple solvothermal and hydrothermal methods

Controlling the size and morphology of the antimony sulfide nanostructures is important for photocatalytic and photovoltaic applications. Herein, we report a systematic approach to synthesize various nanostructures of antimony sulfide. Based on simple solvothermal and hydrothermal routes antimony sulfide nanorods have been synthesized at different temperatures. The size of the nanorods and the morphology of the constituent nano-units, in the form of nanorods, dumbbell and sphere have been controlled by adjusting the temperature. The changes have been confirmed by scanning electron microscope and transmission electron microscope analysis. - Highlights: • We prepared dumbbell structured Sb{sub 2}Sb{sub 3} by simple solvothermal and hydrothermal method. • Investigated the importance of bath temperature on the formation of various structures. • Growth mechanism of dumbbell like structured Sb{sub 2}S{sub 3} nanorods was estimated.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Microstructural, optical and electrical investigations of Sb-SnO{sub 2} thin films deposited by spray pyrolysis

Highlights: • We controlled structural, morphological, electrical, optical and physical (such as band gap energy) properties by altering the Sb doping concentration. • Variation in bandgap with Sb concentration is in agreement with the Burstein–Moss hypothesis and this hypothesis was further confirmed by plotting E{sub g} vs n{sup 2/3}. • The resistivity and mobility are in the range of 1.512–6.624 × 10{sup −3} Ω cm and 9.75–22.96 cm{sup 2} V{sup −1} s{sup −1}. The e-density lies between 4.11 × 10{sup 19} and 4.24 × 10{sup 20} cm{sup −3}. • We observed that Sb substitution in SnO{sub 2} lattice decreases the crystallite size and the possible reason for this is the creation of Sb monolayer on the surface of SnO{sub 2} crystallite. - Abstract: The structural, optical and electrical properties of spray deposited antimony (Sb) doped tin oxide (SnO{sub 2}) thin films, prepared from SnCl{sub 4} precursor, have been studied as a function of antimony doping concentration. The doping concentration was varied from 0 to 1.5 wt.% of Sb. The analysis of X-ray diffraction patterns revealed that the as deposited doped and undoped tin oxide thin films are pure crystalline tetragonal rutile phase of tin oxide which belongs to the space group P4{sub 2}/mnm (number 136). The surface morphological examination with field emission scanning electron microscopy (FESEM) revealed the fact that the grains are closely packed and pores/voids between the grains are very few. The resistivity (ρ) and mobility (μ) are in the range of 1.512 × 10{sup −3}–6.624 × 10{sup −3} Ω cm and 9.75–22.96 cm{sup 2} V{sup −1} s{sup −1}. The electron density lies between 4.11 × 10{sup 19} and 4.24 × 10{sup 20} cm{sup −3}. A thorough electrical investigation reveals that the film's resistivity depends on carrier concentration. It is found that ionized impurity scattering is the dominant mechanism, which limits the mobility of the carriers. The transmittance spectra for as-deposited films were recorded in the wavelength range of 200–1000 nm. The transmittance of the films was observed to increase from 57% to 68% (at 800 nm) on initial addition of Sb (up to [Sb]/[Sn] = 0.5 wt.%) and then it is decreased for higher level of antimony doping ([Sb]/[Sn] >0.5 wt.%)

36 MATERIALS SCIENCE↗
DOE OSTI2016

Compositional analysis of dilute nitride doped indium antimonide bulk crystal by VDS technique

Dilute nitrides are suitable materials for fabrication of devices in detection of long wavelength infrared region. Dilute nitride doped Indium antimonide bulk crystals were grown using vertical directional solidification technique. The compositional characteristics of the crystals were carried out using EDS. The analysis was simulated and compared with observations using DTSA II software for accuracy. The ingots have uniform composition of Indium and Antimony. The actual nitrogen composition measured using EDS was 0.136% for doped nitrogen composition 0.1% except near conical end where it was 0.1%. The study of bonding between nitrogen, Indium and antimony was carried out using SIMS. The analysis shows strong presence of In-N bonding along with In-Sb bonds which indicates nitrogen has replaced antimony atoms in crystal lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Monolayer-by-monolayer compositional analysis of InAs/InAsSb superlattices with cross-sectional STM

In this paper, we use cross-sectional scanning tunneling microscopy (STM) to reconstruct the monolayer-by-monolayer composition profile across a representative subset of MBE-grown InAs/InAsSb superlattice layers and find that antimony segregation frustrates the intended compositional discontinuities across both antimonide-on-arsenide and arsenide-on-antimonide heterojunctions. Graded, rather than abrupt, interfaces are formed in either case. We likewise find that the incorporated antimony per superlattice period varies measurably from beginning to end of the multilayer stack. Finally, although the intended antimony discontinuities predict significant discrepancies with respect to the experimentally observed high-resolution x-ray diffraction spectrum, dynamical simulations based on the STM-derived profiles provide an excellent quantitative match to all important aspects of the x-ray data.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Experimental Findings on Minor Actinide and Lanthanide Separations using Ion Exchange

During FY14, experimental work focused in the following areas: (1) synthesis, characterization and testing of ion-exchange materials and (2) investigating methods to oxidize americium(III) in dilute nitric acid using peroxydisulfate. Ion-exchange materials tested at SRNL included antimony silicates. Inorganic and hybrid ion-exchange materials tested previously in this project are limited to a pH of about 2. In more concentrated acid solutions, the ion-exchange material is chemically unstable or exhibits poor ion-exchange performance for metal ions. FY14 research focused on testing antimony silicates, which had been reported to exhibit good ion-exchange in 0.2 – 1.0 M nitric acid and some ion-exchange capacity in as high as 3 M nitric acid. Performance testing of archived antimony silicate samples from Prof. R. Harjula (U. Helsinki) and freshly prepared samples showed very low affinity for lanthanide ions in 0.1, 1.0 and 3.0 M nitric acid. Tests carried out in FY14 continued work initiated the previous year to understand the effects that Pu(IV) and nitrite have on the oxidation of Am(III) by peroxydisulfate. Findings indicate that both Pu(IV) and nitrite are oxidized by peroxydisulfate. Consequently, an excess of peroxydisulfate is needed to maximize the conversion of Am(III) to Am(V).

Hobbs, D. T.↗
DOE OSTI2018

Purification of Zirconium Tetrachloride from UNF Cladding

The overarching objective of this project was to design and demonstrate (laboratory scale) a sublimation-based purification protocol to obtain pure zirconium chloride (ZrCl 4 ) from impure feeds derived from the direct chlorination of Zircaloy cladding materials. To achieve this objective the following goals were identified. (1) Design, construct and test an apparatus capable of subliming and purifying ZrCl 4 at room pressure and temperatures between 600 and 700K (sublimation point of ZrCl 4 606 K). (2) Investigate reactions that may be used to chemically alter the makeup of the impure ZrCl 4 feed materials to enhance their removal from ZrCl 4 in the sublimation-purification process. (3) Computationally model the reactions of metal chlorides in the gas phase under sublimation conditions (1 atm, 600 K) to determine if oligomers are formed and, if formed, how they would influence sublimation-based purification strategies. All experimental investigations performed as part of this project used stable (non-radioactive) compounds and materials as surrogates for the impure ZrCl 4 feedstocks that would be derived from the direct chlorination of Zircaloy claddings from spent nuclear fuel rods. No radiologically active materials were used at any time in this project. The impure ZrCl 4 feedstocks used in this study were derived from the direct chlorination of virgin Zircaloy claddings (Zirc-2, -4 and high Nb). The main goals of the project have been achieved during the three year period of this NEUP sponsored project. The impurities of greatest concern in the feedstocks were identified as the chloride salts of the alloying metals originally found in Zircaloy (Fe, Nb) and radiological contaminants (Cs, Sr, and Sb). A series of prototype sublimation apparatuses and heating arrangements were designed, constructed and tested. A general batch-sublimator design was identified and a 1.0 kg batch sublimator/oven system was fabricated from glass. Purification protocols developed on small scale runs were found to scale to 1.0 kg batches without problem. Purification factor ranges (PFs: wt% final / wt% initial ) for the impurity chlorides identified above have been measured: Fe (40 – 500); Nb (10 – 70); Cs (520 – 5000); Sr (250 – 1900); Sb (220 – 2300). Removal of iron is sensitive to the partial pressure of hydrogen (in nitrogen) flowing through the system. Lower PFs are obtained when the hydrogen partial pressure is lower. Lower flows are required to raise the iron PF. Removal of niobium is very sensitive to the endpoint determination of the forerun. When judged properly (color change yellow to white in sublimate) reasonable PFs (500) can be achieved. However, as discussed in the conclusions section, endpoint determination can be difficult and significantly lower PFs may be obtained when the endpoint is not correctly identified. Several methods of obtaining quantitative cesium, strontium and antimony PFs were investigated, the best being ICP-MS. The results reported here reflect very limited access to and ICP-MS instrument during the course of this project. It should be noted that, while significantly reduced amounts of antimony are observed in the product, antimony is also found in the exhaust trap after the condenser. Quantum chemical computational modeling studies of the reactions of metal chlorides in the gas phase provided important information about a chemical transport mechanism that could defeat sublimation-based purification strategies. Many metal chlorides are known to oligomerize in the gas phase to reduce their coordinative unsaturation. Dimerization of ZrCl 4 with iron or niobium chlorides would provide a mechanism by which both metal impurities could be carried over with the product during sublimation of the bulk material. Computational modeling conclusively showed that under sublimation conditions in the gas phase, dimerization reactions are not favored thermodynamically due to a significant entropic penalty for the reaction. Therefore, consistent with experimental observations, sublimation-based purification strategies remain viable. The experimental part of the report concludes with a short discussion of the issues that still remain in developing a technologically relevant Zircaloy recycling strategy. The final section of the report is a summary of the quantum chemical investigation of the reactions of metal chlorides in the gas phase under sublimation conditions.

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

Exploring the Feasibility and Performance of Perovskite/Antimony Selenide Four-Terminal Tandem Solar Cells

The tandem solar cell presents a potential solution to surpass the Shockley–Queisser limit observed in single-junction solar cells. However, creating a tandem device that is both cost-effective and highly efficient poses a significant challenge. In this study, we present proof of concept for a four-terminal (4T) tandem solar cell utilizing a wide bandgap (1.6–1.8 eV) perovskite top cell and a narrow bandgap (1.2 eV) antimony selenide (Sb 2 Se 3 ) bottom cell. Using a one-dimensional (1D) solar cell capacitance simulator (SCAPS), our calculations indicate the feasibility of this architecture, projecting a simulated device performance of 23% for the perovskite/Sb 2 Se 3 4T tandem device. To validate this, we fabricated two wide bandgap semitransparent perovskite cells with bandgaps of 1.6 eV and 1.77 eV, respectively. These were then mechanically stacked with a narrow bandgap antimony selenide (1.2 eV) to create a tandem structure, resulting in experimental efficiencies exceeding 15%. The obtained results demonstrate promising device performance, showcasing the potential of combining perovskite top cells with the emerging, earth-abundant antimony selenide thin film solar technology to enhance overall device efficiency.

14 SOLAR ENERGY↗
NASA NTRS1971

Use of radiation in preparative chemistry

A summary and updating of previous work on the use of radiation chemistry for the preparation of pure materials are presented. Work was chiefly concerned with the reduction of metal salts in solution to the free metal using 2 MeV electrons. Metals deposited from aqueous solution are copper, silver, zinc, cadmium, thallium, tin, lead, antimony, iron, nickel, cobalt, and palladium. Dry organic solvents were evaluated for the deposition of metals based on a study involving deposition of antimony from soltions of antimony (III) chloride. The use of organic liquids for the preparation of anhydrous metal halides is also presented. Reaction mechanisms for both organic liquids and aqueous system are discussed.

Philipp, W. H.↗
NASA NTRS1981

X-ray photoemission studies of superficially oxidized cesium antimonide photoemitters

Superficially oxidized cesium antimonide photoemitting surfaces prepared in ultrahigh vacuum were studied by X-ray photoelectron spectroscopy. Oxidation of Cs3Sb to produce a surface with enhanced photosensitivity converts part of the antimony to elemental antimony and part of the cesium to cesium suboxide. The latter is identified on the basis of an O1 s peak at 531.3 eV, characteristic of Cs11O3. The production of Cs2O is not ruled out in this process since its signature at 527.5 eV is masked by an antimony shake-up peak at 527 eV.

Bates, C. W., Jr.↗
DOE OSTI2014

Oven rack having integral lubricious, dry porcelain surface

A lubricious glass-coated metal cooking article capable of withstanding repeated heating and cooling between room temperature and at least 500.degree. F. without chipping or cracking the glass coating, wherein the glass coating includes about 0.1 to about 20% by weight of a homogeneously distributed dry refractory lubricant material having a particle size less than about 200 .mu.m. The lubricant material is selected from the group consisting of carbon; graphite; boron nitride; cubic boron nitride; molybdenum (FV) sulfide; molybdenum sulfide; molybdenum (IV) selenide; molybdenum selenide, tungsten (IV) sulfide; tungsten disulfide; tungsten sulfide; silicon nitride (Si.sub.3N.sub.4); TiN; TiC; TiCN; TiO.sub.2; TiAlN; CrN; SiC; diamond-like carbon; tungsten carbide (WC); zirconium oxide (ZrO.sub.2); zirconium oxide and 0.1 to 40 weight % aluminum oxide; alumina-zirconia; antimony; antimony oxide; antimony trioxide; and mixtures thereof.

01 COAL, LIGNITE, AND PEAT↗