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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Transport and optical properties of the chiral semiconductor Ag 3 AuSe 2

Previous band structure calculations predicted Ag 3 AuSe 2 to be a semiconductor with a band gap of approximately 1 eV. Here, we report single crystal growth of Ag 3 AuSe 2 and its transport and optical properties. Single crystals of Ag 3 AuSe 2 were synthesized by slow-cooling from the melt, and grain sizes were confirmed to be greater than 2 mm using electron backscatter diffraction. Optical and transport measurements reveal that Ag 3 AuSe 2 is a highly resistive semiconductor with a band gap and activation energy around 0.3 eV. Our first-principles calculations show that the experimentally determined band gap lies between the predicted band gaps from GGA and hybrid functionals. We predict band inversion to be possible by applying tensile strain. The sensitivity of the gap to Ag/Au ordering, chemical substitution, and heat treatment merit further investigation.

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

Materials Data on AuSe by Materials Project

AuSe crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two AuSe sheets oriented in the (1, 0, 0) direction. there are two inequivalent Au2+ sites. In the first Au2+ site, Au2+ is bonded in a square co-planar geometry to four equivalent Se2- atoms. All Au–Se bond lengths are 2.53 Å. In the second Au2+ site, Au2+ is bonded in a linear geometry to two equivalent Se2- atoms. Both Au–Se bond lengths are 2.44 Å. Se2- is bonded in a 3-coordinate geometry to three Au2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AuSe by Materials Project

AuSe crystallizes in the monoclinic C2/m space group. The structure is one-dimensional and consists of two AuSe ribbons oriented in the (0, 1, 0) direction. there are two inequivalent Au2+ sites. In the first Au2+ site, Au2+ is bonded in a square co-planar geometry to four equivalent Se2- atoms. All Au–Se bond lengths are 2.54 Å. In the second Au2+ site, Au2+ is bonded in a linear geometry to two equivalent Se2- atoms. Both Au–Se bond lengths are 2.47 Å. Se2- is bonded in a 3-coordinate geometry to three Au2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AuSe by Materials Project

AuSe is Modderite-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Au2+ is bonded to six equivalent Se2- atoms to form a mixture of distorted edge, face, and corner-sharing AuSe6 octahedra. The corner-sharing octahedral tilt angles are 51°. All Au–Se bond lengths are 2.80 Å. Se2- is bonded in a 6-coordinate geometry to six equivalent Au2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag(AuS)2 by Materials Project

Ag(AuS)2 crystallizes in the monoclinic Pc space group. The structure is three-dimensional. there are two inequivalent Au+1.50+ sites. In the first Au+1.50+ site, Au+1.50+ is bonded in a distorted linear geometry to two S2- atoms. There are one shorter (2.32 Å) and one longer (2.34 Å) Au–S bond lengths. In the second Au+1.50+ site, Au+1.50+ is bonded in a linear geometry to two equivalent S2- atoms. Both Au–S bond lengths are 2.33 Å. Ag1+ is bonded in a 4-coordinate geometry to four S2- atoms. There are a spread of Ag–S bond distances ranging from 2.50–2.97 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to three Au+1.50+ and one Ag1+ atom to form distorted corner-sharing SAgAu3 tetrahedra. In the second S2- site, S2- is bonded in a 4-coordinate geometry to one Au+1.50+ and three equivalent Ag1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2Cd(AuS)4 by Materials Project

K2Cd(AuS)4 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. K1+ is bonded in a 8-coordinate geometry to two equivalent Au1+ and six equivalent S2- atoms. Both K–Au bond lengths are 3.57 Å. There are a spread of K–S bond distances ranging from 3.33–3.47 Å. There are two inequivalent Au1+ sites. In the first Au1+ site, Au1+ is bonded in a 2-coordinate geometry to two equivalent K1+ and two equivalent S2- atoms. Both Au–S bond lengths are 2.34 Å. In the second Au1+ site, Au1+ is bonded in a distorted linear geometry to two equivalent S2- atoms. Both Au–S bond lengths are 2.34 Å. Cd2+ is bonded in a 4-coordinate geometry to four equivalent S2- atoms. All Cd–S bond lengths are 2.66 Å. S2- is bonded in a 6-coordinate geometry to three equivalent K1+, two Au1+, and one Cd2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AuS by Materials Project

AuS is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Au2+ is bonded to four equivalent S2- atoms to form corner-sharing AuS4 tetrahedra. There are one shorter (2.42 Å) and three longer (2.48 Å) Au–S bond lengths. S2- is bonded to four equivalent Au2+ atoms to form corner-sharing SAu4 tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS1984

First Results of GPS Time Transfer to Australia

A global positioning system (GPS) time transfer unit was installed at Tidbinbilla Deep Space Communications Complex of the DSN in June 1983. It was used to estimate the relationship to UTC(USNO MC) of the Tidbinbilla frequency and time system TID(FTS) based on a hydrogen maser, and to estimate the performance of the Australian free-running time scale UTC(AUS). Data from the first 3 months were analyzed three ways: by two-hop common view using JPL as intermediary; by long-arc interpolation of measurements against space vehicle clocks; and by long arc interpolation of GPS-Time results. Residuals from a single quadratic fit through 3 months of UTC(USNO MC) -TID(FTS) results were white noise with standard error 15 ns, and a flying clock measurement gave 70 ns agreement. A straight line fit through results UTC(USNO MC) - UTC(AUS) gave 90 ns standard error and 120 ns agreement. It is proposed to use the GPS measurements to steer UTC(AUS) to UTC(BIH), and to rename the existing time scale TA(AUS).

Mck.luck, J.↗
NASA NTRS1985

First results of GPS time transfer to Australia

A Global Positioning System time transfer unit built by NBS under contract to JPL was installed at Tidbinbilla Deep Space Communications Complex of the NASA Deep Space Network in June 1983. It has been used to estimate the relationship to UTC(USNO MC) of the Tidbinbilla frequency and time system TID(FTS) based on a hydrogen maser, and thence to estimate the performance of the Australian free-running time scale UTC(AUS). Data from the first three months has been analyzed three ways: by two-hop common view using JPL as intermediary; by long-arc interpolation of measurements against space vehicle clocks; and by long-arc interpolation of GPS-Time results. Residuals from a single quadratic fit through three months of UTC(USNO MC) - TID (FTS) results were white noise with standard error 15 ns, and a flying clock measurement gave 70 ns agreement. A straight line fit through results UTC(USNO MC) - UTC (AUS) gave 90 ns standard error and 120 bns agreement. It is proposed to use the GPS measurements to steer UTS(AUS) to UTC(BIH), and to rename the existing time scale TA(AUS).

Luck, J. M.↗
DOE OSTI2024

Reduktive Eliminierung von Tetraalkylcupraten [Me n Cu(CF 3 ) 4− n ] − ( n =0–4): jenseits einfacher Oxidationsstufen

Abstract In den letzten Jahren haben Organocuprate im Allgemeinen und der Komplex [Cu(CF 3 ) 4 ] − im Besonderen wegen ihrer elektronischen Strukturen erhebliches Interesse auf sich gezogen. Obwohl der Reaktivität dieser Spezies in diesem Zusammenhang eine Schlüsselrolle zukommen dürfte, fand dieser Aspekt bisher nur wenig Beachtung. Wir untersuchen hier systematisch die Reihe der Tetraalkylcuprate [Me n Cu(CF 3 ) 4− n ] − und ihre Gasphasenreaktivität, die sowohl konzertierte reduktive Eliminierungen als auch Radikalverluste umfasst. Mit Hilfe quantenchemischer Rechnungen charakterisieren wir die elektronischen Strukturen der Komplexe und zeigen, wie sie mit der Reaktivität zusammenhängen. Wir finden, dass alle Ionen [Me n Cu(CF 3 ) 4− n ] − invertierte Ligandenfelder aufweisen und dass sich die unterschiedlichen Reaktivitäten der individuellen Komplexe aus dem Zusammenspiel verschiedener Effekte ergeben.

Zimmer, Bastian↗
DOE OSTI2020

Enhanced Nanostructure Dynamics on Au(111) with Adsorbed Sulfur due to Au–S Complex Formation

Chemisorbed species can enhance the fluxional dynamics of nanostructured metal surfaces which has implications for applications such as catalysis. Scanning tunneling microscopy studies at room temperature reveal that the presence of adsorbed sulfur (S) greatly enhances the decay rate of 2D Au islands in the vicinity of extended step edges on Au(111). This enhancement is already significant at S coverages, θS, of a few hundredths of a monolayer (ML), and is most pronounced for 0.1–0.3 ML where the decay rate is increased by a factor of around 30. For θ S close to saturation at about 0.6 ML, sulfur induces pitting and reconstruction of the entire surface, and Au islands are stabilized. Enhanced coarsening at lower θS is attributed to the formation and diffusion across terraces of Au–S complexes, particularly AuS 2 and Au4S 4 , with some lesser contribution from Au3S4. This picture is supported by density functional theory analysis of complex formation energies and diffusion barriers.

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

Modeling diurnal and annual ethylene generation from solar-driven electrochemical CO 2 reduction devices

Integrated solar fuels devices for CO 2 reduction (CO 2 R) are a promising technology class towards reducing carbon emissions. Designing integrated CO 2 R solar fuels devices requires careful co-design of electrochemical and photovoltaic components as well as consideration of the diurnal and seasonal effects of solar irradiance, temperature, and other meteorological factors expected for ‘on-sun’ deployment. Using a photovoltaic-electrochemical (PV-EC) platform, we developed a temperature and potential-dependent diurnal and annual model using experimentally-determined CO 2 R performance of Cu-based electrocatalysts, local meteorological data from the National Solar Radiation Database (NSRD), and modeled performance of commercial c-Si PVs. Here we simulated gaseous diurnal product outputs with and without the effects of ambient temperature. From these outputs, we observed seasonal variation in gaseous product generation, with up to two-fold increases in ethylene productivity between the Winter and Summer, analyzed the consequences of dynamic cloud coverage, and identified periods where device cooling/heating mechanisms could be implemented to maximize ethylene generation. Finally, we modeled the annual ethylene generation for a scaled 1 MW solar farm at three different locations (Beijing, CN; Sydney, AUS; Barstow, CA) to determine the consequences of local meteorological climates on PV-EC CO 2 R product output, recording a maximum ethylene output of 18.5 tonne per year at Barstow. Overall, this model presents a critical tool for streamlining the translation of experimental solar-driven electrochemical research to real-world implementation.

14 SOLAR ENERGY↗
DOE OSTI2024

Modeling Diurnal and Annual Ethylene Generation from Solar-Driven Electrochemical CO 2 Reduction Devices

Integrated solar fuels devices for CO 2 reduction (CO 2 R) are a promising technology class towards achieving net-negative carbon emissions. Designing integrated CO 2 R solar fuels devices requires careful co-design of electrochemical and photovoltaic components as well as consideration of the diurnal and seasonal effects of solar irradiance, temperature, and other meteorological factors expected for ‘on-sun’ deployment. Here, using a photovoltaic-electrochemical (PV-EC) platform, we developed a temperature and potential-dependent diurnal and annual model using experimental CO 2 R performance of Cu-based electrocatalysts, local meteorological data from the National Solar Radiation Database (NSRD), and modeled performance of commercial c-Si PVs. We simulated diurnal product outputs with and without the effects of ambient temperature to determine gaseous product temperature sensitivity. From these outputs, we observed seasonal variation in gaseous product generation, with up to two-fold increases in ethylene productivity between the Winter and Summer, analyzed the consequences of dynamic cloud coverage, and identified periods where device cooling/heating mechanisms could be implemented to maximize ethylene generation. Finally, we modeled the annual ethylene generation for a scaled 1 MW solar farm at three different locations (Beijing, CN; Sydney, AUS; Barstow, CA) to determine the consequences of local meteorological climates on PV-EC CO 2 R product output, recording a maximum ethylene output of 18.5 tonne/yr at Barstow. Overall, this model presents a critical tool for streamlining the translation of experimental solar-driven electrochemical research to real-world implementation.

Yap, Kyra M. K.↗
DOE OSTI2021

Tempering and Austempering of Double Soaked Medium Manganese Steels

The addition of a tempering or austempering step to the double soaking of a 0.14C–7.17Mn (wt pct) steel was investigated in the present contribution. The double soaking heat treatment is a two-step intercritical annealing heat treatment, which generates microstructures of athermal martensite, retained austenite and ferrite when applied to medium manganese steels. Microstructures following double soaking and (aus)tempering contained a combination of retained austenite, athermal or tempered martensite, and blocky or bainitic ferrite. X-ray diffraction, dilatometry and transmission Kikuchi diffraction were utilized to investigate microstructural changes which occurred during tempering or austempering. The resulting mechanical properties were measured using uniaxial tensile testing. The double soaking plus tempering heat treatment was shown to generate an ultimate tensile strength of 1,340 MPa in combination with 28 pct total elongation while the double soaking plus austempering heat treatment resulted in an ultimate tensile strength of 1,675 MPa and total elongation of 22 pct. Overall, both novel heat treatments produced a combination of strength and ductility desired for the third generation of advanced high strength steels.

36 MATERIALS SCIENCE↗
NASA NTRS1975

On Similarity Transformation and Geodetic Network Distortions Based on Doppler Satellite Observations

Models used in geodesy to transform two sets of coordinates are studied and distortions in geodetic networks are investigated. Commonly used transformation models are first reviewed and most of them are interpreted. Differences between various models are discussed. Pitfalls in partial solutions are then considered. It is shown that only as many chords and/or directional elements can be used in the computation as are needed to completely determine the size or shape of the polyhedron implied in the set of Cartesian coordinates. Each additional element causes the normal matrix to be singular provided that all correlations between the chords are used. A number of tables and maps indicating distortions in the NAD 27, Precise Traverse M-R '72, AUS, and SAD 69 geodetic datums are also included. The residuals of the coordinates are scanned for systematic patterns after transforming each geodetic system to the NWL9D Doppler system. Also, an attempt is made to show scale distortions in the NAD 27.

Leick, Alfred↗
NASA NTRS1988

The CSM testbed matrix processors internal logic and dataflow descriptions

This report constitutes the final report for subtask 1 of Task 5 of NASA Contract NAS1-18444, Computational Structural Mechanics (CSM) Research. This report contains a detailed description of the coded workings of selected CSM Testbed matrix processors (i.e., TOPO, K, INV, SSOL) and of the arithmetic utility processor AUS. These processors and the current sparse matrix data structures are studied and documented. Items examined include: details of the data structures, interdependence of data structures, data-blocking logic in the data structures, processor data flow and architecture, and processor algorithmic logic flow.

Regelbrugge, Marc E.↗