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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

(GeTe){sub n}SbInTe{sub 3} (n≤3)—Element distribution and thermal behavior

Antimony in germanium antimony tellurides (GeTe){sub n}(Sb{sub 2}Te{sub 3}) can be substituted by indium. Homogeneous bulk samples of GeSbInTe{sub 4} (R3-bar m, Z=3, a=4.21324(5) Å, c=41.0348(10) Å) and Ge{sub 2}SbInTe{sub 5} (P3-bar m1, Z=1, a=4.20204(6) Å, c=17.2076(4) Å) were obtained; their structures were refined with the Rietveld method. Single-crystal X-ray diffraction using synchrotron radiation at the K edges of Sb and Te (exploiting anomalous dispersion) yields precise information on the element distribution in the trigonal layered structure of Ge{sub 3}SbInTe{sub 6} (R3-bar m, Z=3, a=4.19789(4) Å, c=62.1620(11) Å). The structure is characterized by van der Waals gaps between distorted rocksalt-type slabs of alternating cation and anion layers. The cation concentration is commensurately modulated with Sb preferring the positions near the gaps. In contrast to unsubstituted Ge{sub 3}Sb{sub 2}Te{sub 6}, quenching the NaCl-type high-temperature phase (stable above ∼510 °C) easily yields a pseudocubic modification that is metastable at ambient conditions. Temperature-dependent powder diffraction reveals a broader stability range of the cubic high-temperature modification of Ge{sub 3}SbInTe{sub 6} compared to the ternary phases. In-containing samples partially decompose at ca. 300 °C but become homogeneous again when the high-temperature phase is formed. - Graphical abstract: Crystal structure of 33R-Ge{sub 3}SbInTe{sub 6} as determined by resonant X-ray diffraction, one example of the (GeTe){sub n}SbInTe{sub 3} series of compounds investigated. - Highlights: • The new compounds 21R-GeSbInTe{sub 4}, 9P-Ge{sub 2}SbInTe{sub 5} and 33R-Ge{sub 3}SbInTe are described. • The element distribution in 33R-Ge{sub 3}SbInTe{sub 6} was determined by resonant scattering. • The cation concentration in the crystal structure is strongly modulated. • The Sb substitution by In has a significant impact on phase transitions. • Results may be relevant for thermoelectrics and thin-film phase-change materials.

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

Thermoelectric properties of p-type Ag{sub 1−x}(Pb{sub 1−y}Sn{sub y}){sub m}Sb{sub 1−z}Te{sub m+2}

The thermoelectric properties of Ag{sub 1−x}(Pb{sub 1−y}Sn{sub y}){sub m}Sb{sub 1−z}Te{sub m+2} (4≤m≤16, −0.1≤x≤0.3, 1/3≤y≤2/3, 0.2≤z≤0.4; Lead Antimony Silver Tellurium Tin, LASTT-m) compositions were investigated in the temperature range of 300 to ~670 K. All samples crystallize in the average NaCl-type structure without any noticeable second phase and exhibit very narrow bandgaps of <0.1 eV. We studied a range of m values, silver concentrations (x), Pb/Sn ratios (y), and antimony concentrations (z) to determine their effects on the thermoelectric properties. The samples were investigated as melt grown polycrystalline ingots. Varying the Ag contents, the Pb/Sn ratios, and the Sb contents off-stoichiometry allowed us to control the electrical conductivity, the Seebeck coefficient, and the thermal conductivity. The electrical conductivity tends to decrease with decreasing m values. The highest ZT of ~1.1 was achieved at ~660 K for Ag{sub 0.9}Pb{sub 5}Sn{sub 5}Sb{sub 0.8}Te{sub 12} mainly due to the very low lattice thermal conductivity of ~0.4 W/(m K) around 660 K. Also, samples with charge-balanced stoichiometries, Ag(Pb{sub 1−y}Sn{sub y}){sub m}SbTe{sub m+2}, were studied and found to exhibit a lower power factor and higher lattice thermal conductivity than the Ag{sub 1−x}(Pb{sub 1−y}Sn{sub y}){sub m}Sb{sub 1−z}Te{sub m+2} compositions. - Graphical abstract: The Ag{sub 1−x}(Pb{sub 1−y}Sn{sub y}){sub m}Sb{sub 1−z}Te{sub m+2} system defines a complex and flexible class of tunable thermoelectric class of materials with high performance.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Lead sheathing of ship hulls in the Roman period: Archaeometallurgical characterisation

An archaeometallurgical analysis of samples of lead sheathing from five ships of the Roman period was carried out in order to determine their composition and microstructure, and to obtain a better understanding of their manufacturing processes. The examinations included optical microscopy of metallographic cross-sections, microhardness tests, scanning electron microscopy, including energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The results show that the samples were all composed of lead covered with an oxide layer. The sheet thicknesses, microhardness values and microhardness distribution, as well as the grain size distribution, led to the conclusion that all of the sheets were produced by the same technology, using hammering, and were probably used for the same purpose. The presence of antimony was observed in the sample from the Roman ship from Caesarea, which may hint at an Italian (Sardinian) origin of the material, and perhaps of the ship. - Research Highlights: {yields} During the Roman period ship hulls were sheathed with lead. {yields} Five samples have been analysed for their characteristics and manufacturing process. {yields} The process was cold-working (strain-hardening) using hammering. {yields} The lead was open-casted on a flat stone, and later hammered at room temperature. {yields} Antimony in the Caesarea shipwreck may indicate an Italian origin of construction.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Enhanced Li- and Na-storage in Sb-Graphene nanocomposite anodes

Highlights: • Antimony-graphene nanocomposite (Sb-GNP) was prepared by a wet-chemical approach. • Sb-GNP exhibits the well-dispersed Sb nanoparticles anchored on the graphenes. • Sb-GNP shows highly reversible capacities in both Li- and Na-storage. - Abstract: Antimony-graphene nanocomposite (Sb-GNP) was prepared from commercially available graphene nanoplatelets (GNPs) by a simple wet-chemical route at room temperature, and systematically investigated as an anode material for both lithium- and sodium-ion batteries (LIBs and NIBs). The microstructural features of Sb-GNP, and of pure Sb nanoparticles prepared without addition of GNPs, were characterized using X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. The successful formation of a nanocomposite structure was observed for Sb-GNP; the Sb nanoparticles are well dispersed and anchored on graphene nanoplatelets without significant aggregation of Sb nanoparticles, in contrast to the pure Sb nanoparticles. Furthermore, galvanostatic studies revealed that Sb-GNP displays better Li- and Na-storage performance than the pure Sb nanoparticles when utilized as an anode material. The enhanced electrochemical performance can be attributed to the effects of nanocomposite formation with GNPs.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Synthesis, structure, and properties of a T-shaped 14-electron stiboranyl-gold complex.

A cyclic stiboranyl-gold complex (1) supported by two 1,8-naphthalenediyl linkers has been synthesized and structurally characterized. The gold atom of this complex adopts a T-shaped geometry and is separated from the antimony center by only 2.76 {angstrom}. Surprisingly, the trivalent gold atom of this complex is involved in an aurophilic interaction, a phenomenon typically only observed for monovalent gold complexes. This phenomenon indicates that the stiboranyl ligand possesses strong {sigma}-donating properties making the trivalent gold atom of 1 electron rich. This view is supported by DFT calculations as well as Au L{sub 3}- and Sb K-edge XANES spectra which reveal that 1 may also be described as an aurate-stibonium derivative. In agreement with this view, complex 1 shows no reactivity toward the halides Cl{sup -}, Br{sup -}, and I{sup -}. It does, however, rapidly react with F{sup -} to form an unprecedented anionic aurate fluorostiborane complex ([2]{sup -}) which has been isolated as the tetra-n-butylammonium salt. The increased coordination number of the antimony center in this anionic complex ([2]{sup -}) does not notably affect the Au-Sb separation (2.77 {angstrom}) or the geometry at the gold atom which remains T-shaped.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Transmission electron microscopy study of GaInNAs(Sb) thin films grown by atomic hydrogen-assisted molecular beam epitaxy

The quaternary GaInNAs is a promising material system for use in next generation multijunction photovoltaic devices. We have investigated the effect of introducing antimony on the growth by using transmission electron microscopy and energy dispersive x-ray (EDX) spectroscopy. Two-dimensional growth was observed in GaInNAs films with striation features associated with compositional fluctuation and nanometer scale elemental segregation on the growth front. On the contrary, GaInNAsSb films exhibit uniform contrast throughout. EDX profile indicates uniform compositional distribution, as antimony atoms suppress the surface mobilites of adatoms resulting in a lower probability to generate the favored bonds, such as Ga-N and In-As.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Electronic transport in heavily doped Ag/n-Si composite films

Hall measurements characterized Ag/n-Si composite films 1 micron thick produced by magnetron co-sputtering onto high resistivity Si (111) substrates at 550°C. The targets were Ag and n-type Si doped with 3 × 10{sup 19}/cm{sup 3} of antimony. Films were prepared with 13, 16 and 22 at. % Ag and measured over a temperature range 77–500°K. Conduction takes place at low temperatures by variable rang hopping in localized states at the Fermi level and by thermal activation over grain boundaries at higher temperatures. The Log Resistivity vs 1/kT curves for the three Ag concentrations vary in a similar manner, but decrease in magnitude with increasing Ag due to the smaller number of grain boundaries between Ag nanoparticles occurring with increasing Ag concentration. At low temperatures Hall mobilities are essentially independent of temperature as the carrier densities for the three Ag concentrations are constant from 77 to slightly under 300°K with resistivities varying by small amounts. The mobilities at all Ag concentrations increase with temperature and approach each other as the effects of grain boundaries become less important. This work presents for the first time the effects of metal particles embedded in a semiconductor on the transport properties of carriers in the semiconductor. Though these effects are for a given average particle size most of the results are expected to hold over a range of particle sizes. Free electrons produced in films containing 13 and 16 at. % Ag result in concentrations of 1.5 × 10{sup 19}/cm{sup 3}, one half the antimony doping, while those with 22 at. % Ag, the carrier concentrations are three orders of magnitude higher. These constant carrier concentrations are due to the metal-insulator transition that occurs in doped crystalline and polycrystalline silicon for carrier densities n{sub c} >3.9 × 10{sup 18}/cm{sup 3}. The three orders of magnitude higher carrier concentration produced in films with 22 at. % Ag is argued to be due to doping of the Si matrix by the Ag nanoparticles at this concentration, a doping effect previously observed in ErAs in InGaAs. A discussion of this doping effect is presented that is in keeping with the experimental observations though other factors such as particle size effects need further experimental confirmation. Thermal activation energies and grain boundary barrier heights were obtained from resistivity and Hall mobility data. The barrier heights of 0.360, 0.390 and 0.470 eV measured for films with Ag concentrations of 13, 16 and 22 at. % Ag respectively, are quite high compared to those obtained by other methods used for producing polycrystalline Si (10-100 mev) and need to be considerably reduced in order to increase the efficiency of the detectors for which these Ag/n-Si composite films will be used. Thermal annealing of as-deposited films is suggested as one means to accomplish this result.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis and structural characterization of new dithiocarbamate complexes from Sb(III) and Bi(III)

Twenty new antimony and bismuth dithiocarbamate complexes which employed ten different type of amines have been successfully synthesized. The synthesized complexes with metal to dithiocarbamate ratio at 1:3. Elemental analysis of the complexes gave the general formula of MCl[S{sub 2}CNR’R”]{sub 2} where M = Sb(III), Bi(III); R’ = methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, benzyl; R” = ethanol, methyl, ethyl, propyl, isopropyl, cyclohexyl, benzyl. The complexes were analysed by IR and NMR spectroscopy. The crystal structure of five-coordinated antimony (III) complex have been determined by X-ray single crystal diffraction. Single crystal X-ray diffraction studies on SbCl[S{sub 2}CN(C{sub 4}H{sub 9})(C{sub 2}H{sub 5})]{sub 2} adopted a triclinic system with a space group P1 with a = 10.0141(8) Å, b = 10.1394(7) Å, c = 11.8665(9) Å, α = 67.960°, β =87.616°, γ = 80.172°.

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

Direct observation of bi-alkali antimonide photocathodes growth via in operando x-ray diffraction studies

Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication of the bi-alkali photocathodes, K{sub 2}CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode on Si(100) substrates. The amorphous-to-crystalline transition for the initial antimony layer was observed at a film thickness of 40 Å . The antimony crystalline structure dissolved upon potassium deposition, eventually recrystallizing upon further deposition into K-Sb crystalline modifications. This transition, as well as the conversion of potassium antimonide to K{sub 2}CsSb upon cesium deposition, is correlated with changes in the quantum efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Temperature-dependent optical measurements of the dominant recombination mechanisms in InAs/InAsSb type-2 superlattices

Temperature-dependent measurements of carrier recombination rates using a time-resolved optical pump-probe technique are reported for mid-wave infrared InAs/InAs{sub 1−x}Sb{sub x} type-2 superlattices (T2SLs). By engineering the layer widths and alloy compositions, a 16 K band-gap of ∼235 ± 10 meV was achieved for five unintentionally and four intentionally doped T2SLs. Carrier lifetimes were determined by fitting lifetime models based on Shockley-Read-Hall (SRH), radiative, and Auger recombination processes to the temperature and excess carrier density dependent data. The minority carrier (MC), radiative, and Auger lifetimes were observed to generally increase with increasing antimony content and decreasing layer thickness for the unintentionally doped T2SLs. The MC lifetime is limited by SRH processes at temperatures below 200 K in the unintentionally doped T2SLs. The extracted SRH defect energy levels were found to be near mid-bandgap. Also, it is observed that the MC lifetime is limited by Auger recombination in the intentionally doped T2SLs with doping levels greater than n ∼ 10{sup 16} cm{sup −3}.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Optical absorption and intrinsic recombination in relaxed and strained InAs{sub 1–x}Sb{sub x} alloys for mid-wavelength infrared application

The intrinsic carrier recombination lifetime in relaxed and strained InAs{sub 1−x}Sb{sub x} alloys is investigated using the full-band Green's function theory. By computing the phonon-perturbed electron self-energy of the system, both direct and phonon-assisted indirect Auger and radiative processes are studied as functions of antimony molar fractions, lattice temperatures and applied in-plane biaxial strains. To improve the overall accuracy of the calculation, an empirical pseudopotential band structure for the alloy is also fitted to the measured band extrema and effective masses under different biaxial strains. A set of effective screened potentials valid for all the needed antimony fractions x and biaxial strains ϵ, therefore, is obtained and applied to the calculation. The results showed reduced total Auger recombination rates and enhanced radiative recombination rates in InAsSb alloys at room temperature when a compressive strain is applied. Furthermore, the study on the widely employed mid-wavelength infrared detector material, InAs{sub 0.91}Sb{sub 0.09}, strained by an InAs substrate, demonstrated that much longer minority carrier lifetime can be achieved compared to that in the lattice-matched situation when the lattice temperature is above 200 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Effect of ammonium-sulfide solvent on the surface passivation of GaSb (100)

X-ray photoemission spectroscopy and scanning electron microscopy are used to study the effect of a solvent on the chemical composition of a sulfide passivating layer formed on GaSb (100) surface. Treatment of the GaSb (100) surface with ammonium-sulfide solutions results in the formation of a thick (several tens of nanometers) coating composed of a mixture of various binary and ternary gallium and antimony sulfides. The chemical compositions of the passivating sulfide layers formed in aqueous and alcoholic ammonium-sulfide solutions are different. Annealing of the sulfide layer at 360°C in ultrahigh vacuum leads to the partial desorption of antimony from the surface, the decomposition of ternary sulfides into their binary constituents, and change in the surface band bending of this layer.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Electrochemical Sodiation of FeSb 2 : New Insights from Operando 57 Fe Synchrotron Mössbauer and X-Ray Absorption Spectroscopy

Operando Sb K–edge X–ray absorption spectroscopy and 57 Fe Synchrotron Mössbauer Spectroscopy, used for the first time in the field of operando energy storage materials, assisted by operando magnetic measurements, were combined to clarify the role of iron and antimony in the electrochemical reaction mechanism of FeSb 2 as negative electrode material for sodium–ion batteries (SIB). Both datasets were analyzed using an innovative chemometric approach involving principal component analysis (PCA) and multivariate curve resolution – alternating least square analysis (MCR–ALS) yielding new insights on the sodiation reaction. Our findings show that the reaction of Na with FeSb 2 during discharge leads to the formation of Na 3 Sb along with superparamagnetic Fe amorphous nanoparticles which contain small amounts of Sb dissolved in their lattice. During the following desodiation, the pristine material FeSb 2 is not recovered while iron nanoparticles grow in size, and continue growing also along the following discharge. Here, even though such iron nanoparticles remain electrochemically inactive, they play a key role in the reduction and stabilization of the polarization as well as in the reversibility of the electrochemical sodiation of antimony.

25 ENERGY STORAGE↗
DOE OSTI2024

Interpretable Machine Learning Models for Practical Antimonate Electrocatalyst Performance

Computationally predicting the performance of catalysts under reaction conditions is a challenging task due to the complexity of catalytic surfaces and their evolution in situ, different reaction paths, and the presence of solid-liquid interfaces in the case of electrochemistry. We demonstrate here how relatively simple machine learning models can be found that enable prediction of experimentally observed onset potentials. Inputs to our model are comprised of data from the oxygen reduction reaction on non-precious transition-metal antimony oxide nanoparticulate catalysts with a combination of experimental conditions and computationally affordable bulk atomic and electronic structural descriptors from density functional theory simulations. From human-interpretable genetic programming models, we identify key experimental descriptors and key supplemental bulk electronic and atomic structural descriptors that govern trends in onset potentials for these oxides and deduce how these descriptors should be tuned to increase onset potentials. Here, we finally validate these machine learning predictions by experimentally confirming that scandium as a dopant in nickel antimony oxide leads to a desired onset potential increase. Macroscopic experimental factors are found to be crucially important descriptors to be considered for models of catalytic performance, highlighting the important role machine learning can play here even in the presence of small datasets.

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

New Perspectives in Thermoelectric Energy Recovery System Design Optimization

Abstract: Large amounts of waste heat are generated worldwide in industrial processes, automotive transportation, diesel engine exhaust, military generators, and incinerators because 60-70% of the fuel energy is typically lost in these processes. There is a strong need to develop technologies that recover this waste heat to increase fuel efficiency and minimize fuel requirements in these industrial processes, automotive and heavy vehicle engines, diesel generators, and incinerators. There are additional requirements to reduce CO2 production and environmental footprints in many of these applications. Recent work with the Strategic Environmental Research and Development Program office has investigated new thermoelectric (TE) materials and systems that can operate at higher performance levels and show a viable pathway to lightweight, small form-factor, advanced thermoelectric generator (TEG) systems to recover waste heat in many of these applications. New TE materials include nano-composite materials such as lead-antimony-silver-telluride (LAST) and lead-antimony-silver-tin-telluride (LASTT) compounds. These new materials have created opportunities for high-performance, segmented-element TE devices. New higher-performance TE devices segmenting LAST/LASTT materials with bismuth telluride have been designed and fabricated. Sectioned TEG systems using these new TE devices and materials have been designed. Integrated heat exchanger/TE device system analyses of sectioned TE system designs have been performed creating unique efficiency-power maps that provide better understandings and comparisons of design tradeoffs and nominal and off-nominal system performance conditions. New design perspectives in optimization of sectioned TE design approaches are discussed that provide insight on how to optimize such sectioned TE systems. System performance analyses using ANSYS® TE modeling capabilities have integrated heat exchanger performance models with ANSYS® TE models to extend its analysis capabilities beyond simple constant hot-side and cold-side temperature conditions . Analysis results portray external resistance effects, matched load conditions, maximum power vs. maximum efficiency points simultaneously.

Energy Conversion↗
DOE OSTI2016

Binding and leaching of trace elements in Portland cement pastes

Portland cement contains trace elements originating from the raw materials and the fuels used for cement production. The trace elements are bound to some extent during cement hydration. A small fraction remains dissolved in the pore solution. The dissolved fractions of antimony, barium, chromium, lead, molybdenum and vanadium were quantified in the course of hydration of four different Portland cements. The development of heavy metal concentrations signifies the relevant hydration products for the binding of heavy metals. For chromate and molybdate a substitution for sulfate in ettringite was found. Vanadium and antimony are most likely not bound in ettringite. Barium precipitates as barium sulfate. For lead no clear trends could be observed. Leaching experiments were carried out and the concentrations of the leachates were compared to pore solution concentrations to check if the solubility of the heavy metals is relevant or if the leaching process is controlled by diffusion.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Yolk-shell structured Sb@C anodes for high energy Na-ion batteries

Despite great advances in sodium-ion battery developments, the search for high energy and stable anode materials remains a challenge. Alloy or conversion-typed anode materials are attractive candidates of high specific capacity and low voltage potential, yet their applications are hampered by the large volume expansion and hence poor electrochemical reversibility and fast capacity fade. Here, we use antimony (Sb) as an example to demonstrate the use of yolk-shell structured anodes for high energy Na-ion batteries. The Sb@C yolk-shell structure prepared by controlled reduction and selective removal of Sb2O3 from carbon coated Sb2O3 nanoparticles can accommodate the Sb swelling upon sodiation and improve the structural/electrical integrity against pulverization. It delivers a high specific capacity of ~554 mAh•g-1, good rate capability (315 mhA•g-1 at 10C rate) and long cyclability (92% capacity retention over 200 cycles). Full-cells of O3-Na0.9[Cu0.22Fe0.30Mn0.48]O2 cathodes and Sb@C-hard carbon composite anodes demonstrate a high specific energy of ~130 Wh•kg-1 (based on the total mass of cathode and anode) in the voltage range of 2.0-4.0 V, ~1.5 times energy of full-cells with similar design using hard carbon anodes.

Song, Junhua↗