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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Structural, Optical, and Electronic Properties of Two Quaternary Chalcogenide Semiconductors: Ag 2 SrSiS 4 and Ag 2 SrGeS 4

Quaternary chalcogenide materials have long been a source of semiconductors for optoelectronic applications. Recent studies on the I2-II-IV-X4 (I = Ag, Cu, Li; II = Ba, Sr, Eu, Pb; IV = Si, Ge, Sn; X = S, Se) materials have shown particular versatility and promise among these compounds. These semiconductors take advantage of a diverse bonding scheme and chemical differences among cations to target a degree of anti-site defect resistance. Within this set of compounds, the materials containing both Ag and Sr have not been experimentally studied and leave a gap in the full understanding of the family. Here, we have synthesized powders and single crystals of two Ag- and Sr-containing compounds, Ag 2 SrSiS 4 and Ag 2 SrGeS 4 , each found to form in the tetragonal I4¯2m structure of Ag 2 BaGeS 4 . During the synthesis targeting the title compounds, two additional materials, Ag 2 Sr 3 Si 2 S 8 and Ag 2 Sr 3 Ge 2 S 8 , have also been identified. Furthermore, these cubic compounds represent impurity phases during the synthesis of Ag 2 SrSiS 4 and Ag 2 SrGeS 4 . We show through hybrid density functional theory calculations that Ag 2 SrSiS 4 and Ag 2 SrGeS 4 have highly dispersive band edge states and indirect band gaps, experimentally measured as 2.08(1) and 1.73(2) eV, respectively. Second-harmonic generation measurements on Ag 2 SrSiS 4 and Ag 2 SrGeS 4 powders show frequency doubling capabilities in the near-infrared range.

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

Magnetostructural phase transitions and large magnetic entropy changes in Ag-doped Mn 1–x Ag x CoGe intermetallic compounds

The influence of Ag-doping on the crystallographic structure, magnetic properties, and magnetocaloric effects of Mn 1–x Ag x CoGe (0.01 ≤ x ≤ 0.10) is reported. A transformation of crystal structure from orthorhombic to hexagonal was observed at room temperature. Doping Ag in Mn sites results in a first-order magnetostructural transition near room temperature. Furthermore, a Curie-temperature window of 90 K was obtained between the Curie temperatures of the austenite (Ni 2 In-type) and martensite (TiNiSi-type) phases. Large magnetic entropy change values of ~22.0 and 9.4 J/kg/K, and refrigerant capacity of 308 and 272 J/kg, were found for x = 0.06 and 0.05, respectively, for μ o ΔH = 5 T.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2020

Single-Step Conversion of Ethanol to n-Butene over Ag-ZrO2/SiO2 Catalysts

Ethanol is a promising platform molecule for production of a variety of fuels and chemicals. Of particular interest is producing middle distillate fuels (i.e., jet and diesel blendstock) from renewable ethanol feedstock. State-of-the-art alcohol-to-jet technology requires multiple process steps based on catalytic dehydration of ethanol to form ethylene, followed by sometimes a multi-step oligomerization, and then hydrotreatment and distillation. Here we report on a new catalytic route in which ethanol is directly converted to n-butene (1- and 2-butene mixtures) over Ag-ZrO2/SBA-16, thus offering the potential for a reduction in the number of required processing steps versus conventional alcohol-to-jet technology. This catalyst system provides the balanced metal and Lewis acid sites required to selectively facilitate a cascading sequence of reactions that includes dehydrogenation, aldol condensation, Meerwein–Ponndorf–Verley reduction, dehydration, and hydrogenation. High conversion and selectivity toward either n-butene or 1,3-butadiene is achieved by tuning the hydrogen feed partial pressure and other process/catalyst parameters. With sufficient hydrogen partial pressure 1,3-butadiene is completely and selectively hydrogenated to form n-butene. The reaction mechanism was elucidated through operando-nuclear magnetic resonance investigations coupled with reactivity measurements. Combined experimental-computational investigation reveals how changes in silver and zirconium composition and the silver oxidation state affects reactivity under controlled hydrogen partial pressures and after prolonged run times. Finally, catalyst effectiveness also was demonstrated when using wet ethanol feed, thus highlighting process flexibility in terms of feedstock purity requirements. This work was financially supported by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office, and was performed at the Pacific Northwest National Laboratory (PNNL) under Contract No. DE-AC05-76RL01830 and the National Renewable Energy Laboratory under Contract No. DE-AC36- 08GO28308. Part of the work conducted by S. A. Akhade was performed under the auspices of the U.S. DOE at Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344. This work was partly supported through the PNNL-WSU Distinguished Graduate Research Program for ADW. NMR and XPS experiments were performed using EMSL (grid.436923.9), a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research

Dagle, Vanessa↗
NASA NTRS1992

Study of the oxygen transport through Ag (110), Ag (poly), and Ag 2.0 Zr

The transport of oxygen through high-purity membranes of Ag (110), Ag (poly), Ag (nano), and Ag 2.0 Zr has been studied by an ultrahigh vacuum permeation method over the temperature range of 400-800 C. The data show that there are substantial deviations from ordinary diffusion-controlled transport. A surface limitation has been confirmed by glow-discharge studies where the upstream O2 supply has been partially converted to atoms, which, for the same temperature and pressure, gave rise to over an order of magnitude increase in transport flux. Further, the addition of 2.0 wt percent Zr to the Ag has provided increased dissociative adsorption rates, which, in turn, increased the transport flux by a factor of 2. It was also observed that below a temperature of 630 C, the diffusivity exhibits an increase in activation energy of over 4 kcal/mol, which has been attributed to trapping of the atomic oxygen and/or kinetic barriers at the surface and subsurface of the vacuum interface. Above 630 C, the activation barrier decreases to the accepted value of about 11 kcal/mol for Ag (poly), consistent with zero concentration at the vacuum interface.

Outlaw, R. A.↗
DOE OSTI2017

Dependence of spin pumping and spin transfer torque upon Ni 81 Fe 19 thickness in Ta / Ag / Ni 81 Fe 19 / Ag / Co 2 MnGe / Ag / Ta spin-valve structures

Spin pumping has been studied within Ta / Ag / Ni 81 Fe 19 (0–5 nm) / Ag (6 nm) / Co 2 MnGe (5 nm) / Ag / Ta large-area spin-valve structures, and the transverse spin current absorption of Ni 81 Fe 19 sink layers of different thicknesses has been explored. In some circumstances, the spin current absorption can be inferred from the modification of the Co 2 MnGe source layer damping in vector network analyzer ferromagnetic resonance (VNA-FMR) experiments. However, the spin current absorption is more accurately determined from element-specific phase-resolved x-ray ferromagnetic resonance (XFMR) measurements that directly probe the spin transfer torque (STT) acting on the sink layer at the source layer resonance. Comparison with a macrospin model allows the real part of the effective spin mixing conductance to be extracted. We find that spin current absorption in the outer Ta layers has a significant impact, while sink layers with thicknesses of less than 0.6 nm are found to be discontinuous and superparamagnetic at room temperature, and lead to a noticeable increase of the source layer damping. For the thickest 5-nm sink layer, increased spin current absorption is found to coincide with a reduction of the zero frequency FMR linewidth that we attribute to improved interface quality. Furthermore, this study shows that the transverse spin current absorption does not follow a universal dependence upon sink layer thickness but instead the structural quality of the sink layer plays a crucial role.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Reaction pathway analysis of (Ag x Cu 1-x )(In 0.75 Ga 0.25 )Se 2 with x = 0.75 and 1.0

Reaction pathways during formation of Ag(In 0.75 Ga 0.25 )Se 2 films were investigated by ex-situ characterization of time-progressive reactions using rapid thermal processing at 450 °C under 5% Ar/H 2 Se atmosphere. Composition measurements using energy dispersive x-ray spectroscopy (EDS) and X-ray fluorescence (XRF) show that with Ag/(Ag+Cu) = 1.0, Ga grading and Se uptake occur gradually up to 20 min. With 7 min reaction, there was no sign of a AgInSe 2 phase and only a Ag(In,Ga) 5 Se 8 chalcogenide phase formed. The reaction was completed with formation of Ag(In,Ga)Se 2 and Ag(In,Ga) 5 Se 8 within 20 min. The addition of Cu to the precursor so that Ag/(Ag+Cu) = 0.75 speeds up the reaction and reduces the formation of the Ag(In,Ga) 5 Se 8 phase. EDS and XRF analyses indicated that Ga grading and Se uptake were completed after 10 min. XRD analysis also shows formation of CuInSe 2 on the surface of the sample with Cu after 3.5 min reaction prior to other chalcogenide formation. On the other hand, a strong Ag(In,Ga)Se 2 (112) XRD peak appeared after 5 min reaction compared to 10 min reaction for 100% Ag films. EDS and Raman scattering measurements on the back-side of the films after delamination from the substrate indicated that Ga accumulated in AgGaSe 2 and Ga-Se phases at the back-side of films after 45 min reaction. XRD analysis showed that Ag tends to stay in the stable ζ-Ag 3 (In,Ga) phase during the reaction with Ag/(Ag+Cu) = 1.0, but not with 0.75, and this causes the longer reaction time and the non-uniformity.

14 SOLAR ENERGY↗
DOE OSTI2018

3D graphene aerogels-supported Ag and Ag@Ag3PO4 heterostructure for the efficient adsorption-photocatalysis capture of different dye pollutants in water

Highlights: • 3D graphene aerogels-supported Ag and Ag@Ag3PO4 heterostructure are synthesized. • The composite is effective in adsorption-photocatalysis cationic and anionic dyes. • The apparent adsorption-photocatalysis removal sequence is NR > RhB > MB > MO. • The contributions of adsorption and photocatalysis is different for different dyes. • The composite exhibits the highest catalytic activities with excellent stability. - Abstract: In this paper, we successfully synthesized 3D graphene aerogels-supported Ag and Ag@Ag{sub 3}PO{sub 4} heterostructure (3D Ag/Ag@Ag{sub 3}PO{sub 4}/GA) by the hetero-growth of Ag{sub 3}PO{sub 4} on partly Ag nanoparticles in macroporous 3D graphene aerogels (3D GA), aiming for the efficient adsorption-photocatalysis capture of both cationic (RhB, MB, and NR) and anionic (MO) dyes from aqueous solutions. For the removal of different dyes, the contributions of adsorption and photocatalysis is different and the apparent removal sequence is NR > RhB > MB > MO on the prepared 3D Ag/Ag@Ag{sub 3}PO{sub 4}/GA. Compared with bare Ag{sub 3}PO{sub 4} particles, Ag{sub 3}PO{sub 4}/GO, and Ag/Ag@Ag{sub 3}PO{sub 4}/GO, the prepared 3D Ag/Ag@Ag{sub 3}PO{sub 4}/GA exhibits the highest catalytic activities for the visible light degradation of RhB and MO. The possible mechanism for improved photocatalytic degradation of dyes by the 3D Ag/Ag@Ag{sub 3}PO{sub 4}/GA is proposed based on the active species trapping experiments. Moreover, the good stability and convenient recycling of the prepared 3D Ag/Ag@Ag{sub 3}PO{sub 4}/GA composite further make it have potential application prospect in eliminating organic contaminants.

36 MATERIALS SCIENCE↗
NASA NTRS2020

Ag isotopic and chalcophile element evolution of the terrestrial and martian mantles during accretion: new constraints from Bi, Pd, and Ag metal-silicate partitioning.

The Earth’s timing of accretion and acquisition of moderately volatile compounds is uncertain. Hafnium-W and Mn-Cr isotopic data can bracket the timing of early planetary differentiation and core formation. The Ag-Pd system has also been utilized but its application has been limited by a lack of high pressure and temperature metal-silicate partitioning for Pd and Ag. Be-cause Ag (and Bi) are volatile chalcophile siderophile elements, understanding their early distribution can constrain the origin of volatile elements in differentiated bodies and planets. Unfortunately, neither Ag or Bi have been studied across the wide range of pressure and temperature conditions that are relevant to accretion and core-mantle differentiation. Here, new high-pressure and temperature multi-anvil metal-silicate equilibrium experiments for Bi and Ag have been carried out at conditions relevant to planetary accretion and metal silicate differentiation that allow a more refined and complete understanding of element partitioning during core formation. The new metal-silicate partitioning data utilized to predict the distributions of Bi, Pd, and Ag at conditions of accretion for Earth and Mars and show that the Pd/Ag ratio is significantly fractionated during accretion, allowing for the production of detectable 107Ag anomalies produced while 107Pd (half life = 6.5 M.y.) was still extant. Application of the new partitioning results to Earth shows that D(Bi) and D(Ag) (D = metal/silicate concentration ratio) are lowered due to the effect of pressure and Si alloyed in the metallic liquid, resulting in higher predicted mantle Bi and Ag abundances than in the bulk silicate Earth (BSE), as well as high and variable Pd/Ag. The unradiogenic Ag isotopic composition of the BSE could have been generated by early accretion of volatile-poor (high Pd/Ag) precursors, followed by later accretion of volatile–rich (low Pd/Ag) material, in agreement with earlier studies of Pd-Ag and Mn-Cr (Schönbächler et al., 2010). However, these main accretion phases would have to be followed by segregation of a sulfide liquid (at least 1.5% of magma ocean) at high pressures (>30 GPa), to explain the PUM Bi, Pd, and Ag, as well as Au, Pt, Cu and Ni concentrations as proposed previously. If the early accreted bulk Earth was volatile depleted with high Pd/Ag ratios, portions of the mantle may contain ancient domains that developed positive 107Ag isotopic anomalies (as also argued by noble gases, Nd, W, and Os isotopes). In comparison, Bi, Pd, and Ag concentrations in the martian mantle could have been set by simple metal-silicate equilibrium. Mars accreted and differentiated relatively rapidly, while also developing a deep magma ocean with a high Pd/Ag ratio that could have evolved positive 107Ag anomalies, in contrast to Earth. Measurements on shergottites may reveal these predicted Ag isotopic anomalies.

accretion↗
DOE OSTI2023

Ag Alloying in Cu 2– y Ag y Ba(Ge,Sn)Se 4 Films and Photovoltaic Devices

Trigonal Cu 2 BaGe 1–x Sn x Se 4 (CBGTSe) has recently gained interest as a potential photovoltaic absorber to target mitigation of antisite defect formation in Cu 2 ZnSn(S,Se) 4 . This study examines partial substitution of Cu by Ag as a potential approach to tune the properties of Ag-incorporated CBGTSe in the following aspects: 1) phase stability and crystal structure as a function of Ag content; 2) film morphology and grain structure; 3) charge carrier properties; 4) band positions; and 5) charge carrier kinetics and recombination. Up to 20% of Cu can be substituted by Ag in CBGTSe, while above 20% a phase mixture appears. Increasing Ag content induces larger average grain size and reduced hole carrier densities. In contrast, photoelectron spectroscopy and photoluminescence measurements reveal negligible impact of Ag substitution on ionization potential (≈5.4 eV) and electron affinity (≈3.7 eV). Also, Ag content offers negligible impact on carrier lifetimes (few ns). Consistent with these fundamental properties, solar cells based on two different Ag/(Ag + Cu) ratios (≈0% and ≈20%) show comparable power conversion efficiencies (≈2.7–2.8%). Finally, these results indicate that CBGTSe films and solar cells may be less sensitive to Ag substitution compared to Cu 2 ZnSn(S,Se) 4 , at least at the current level of absorber and device optimization.

14 SOLAR ENERGY↗
DOE OSTI2018

Unveiling the Structural Evolution of Ag 1.2 Mn 8 O 16 under Coulombically Controlled (De)Lithiation

MnO 2 materials are considered promising cathode materials for rechargeable lithium, sodium, and magnesium batteries due to their earth abundance and environmental friendliness. One polymorph of MnO 2 , α-MnO 2 , has 2 × 2 tunnels (4.6 Å × 4.6 Å) in its structural framework, which provide facile diffusion pathways for guest ions. In this work, a silver-ion-containing α-MnO 2 (Ag 1.2 Mn 8 O 16 ) is examined as a candidate cathode material for Li based batteries. Electrochemical stability of Ag 1.2 Mn 8 O 16 is investigated through Coulombically controlled reduction under 2 or 4 molar electron equivalents (e.e.). Terminal discharge voltage remains almost constant under 2 e.e. of cycling, whereas it continuously decreases under repetitive reduction by 4 e.e. Thus, detailed structural analyses were utilized to investigate the structural evolution upon lithiation. Significant increases in lattice a (17.7%) and atomic distances (~4.8%) are observed when x in Li x Ag 1.2 Mn 8 O 16 is >4. Ag metal forms at this level of lithiation concomitant with a large structural distortion to the Mn–O framework. In contrast, lattice a only expands by 2.2% and Mn–O/Mn-Mn distances show minor changes (~1.4%) at x < 2. The structural deformation (tunnel breakage) at x > 4 inhibits the recovery of the original structure, leading to poor cycle stability at high lithiation levels. This report establishes the correlation among local structure changes, amorphization processes, formation of Ag 0 , and long-term cycle stability for this silver-containing α-MnO 2 type material at both low and high lithiation levels.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Iodine Capture by Ag-Loaded Solid Sorbents Followed by Ag Recycling and Iodine Immobilization: An End-to-End Process

Here, this article demonstrates the complete process of I 2(g) capture using Ag-exchanged faujasite (AgX) and Ag-exchanged mordenite (AgZ) zeolite sorbents, the recovery of Ag for recyclability of iodine capture, and the immobilization of iodide (from the elution process) into an iodosodalite waste form, which is chemically and environmentally stable. The gaseous iodine, I 2(g) , was captured in the AgX via chemisorption by Ag and converted to AgI within the aluminosilicate zeolite frameworks. The elution reaction in Na 2 S resulted in the precipitation of Ag 2 S and dissolution of I – and Na + into the aqueous solution, where powdered sorbent showed higher conversion efficiency than the granular form, which is attributed to Na 2 S-solution diffusion limitations in the granules. The Ag 2 S-containing aluminosilicate precipitates were filtered out of the solution, and the filtrate (aqueous solution) was used to synthesize iodosodalite to immobilize iodide. The iodine capture using the recovered Ag 2 S-containing sorbents shows equivalent iodine loadings to the AgX starting material of Q e = 0.355 g/g for powdered material and 0.255 g/g for granular material, demonstrating the potential recycling of Ag for iodine capture as Ag 2 S-based sorbents.

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

Sr(Ag 1− x Li x ) 2 Se 2 and [Sr 3 Se 2 ][(Ag 1− x Li x ) 2 Se 2 ] Tunable Direct Band Gap Semiconductors

Abstract Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid‐state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two‐dimensional Sr(Ag 1− x Li x ) 2 Se 2 layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag 1− x Li x ) 2 Se 2 with x up to 0.45. In addition, a new type of intergrowth compound [Sr 3 Se 2 ][(Ag 1− x Li x ) 2 Se 2 ] was synthesized upon further reaction of Sr(Ag 1− x Li x ) 2 Se 2 with SrSe. Both Sr(Ag 1− x Li x ) 2 Se 2 and [Sr 3 Se 2 ][(Ag 1− x Li x ) 2 Se 2 ] exhibit a direct band gap, which increases with increasing Li substitution ( x ). Therefore, the band gap of Sr(Ag 1− x Li x ) 2 Se 2 can be precisely tuned via fine‐tuning x that is controlled by only the flux ratio and temperature.

Zhou, Xiuquan↗
DOE OSTI2017

Bimetallic Ag-Pt Sub-nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts

A combined experimental and theoretical investigation of Ag-Pt sub-nanometer clusters as heterogeneous catalysts in the CO -> CO2 reaction (COox) is presented. Ag9Pt2 and Ag9Pt3 clusters are size-selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first-principles simulations at realistic coverage. Insitu GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano-aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O-2, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.

Ab initio calculations↗
DOE OSTI2023

Sr(Ag 1-x Li x ) 2 Se 2 and [Sr 3 Se 2 ][(Ag 1-x Li x ) 2 Se 2 ] Tunable Direct Band Gap Semiconductors

Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid-state reactions, leading to crystal formation of kinetically stable compounds. Here, in this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two-dimensional Sr(Ag 1-x Li x ) 2 Se 2 layered phases. With increased LiOH/LiCl ratio or reaction temperature, Li partially substituted Ag to form solid solutions of Sr(Ag 1-x Li x ) 2 Se 2 with x up to 0.45. In addition, a new type of intergrowth compound [Sr 3 Se 2 ][(Ag 1-x Li x ) 2 Se 2 ] was synthesized upon further reaction of Sr(Ag 1-x Li x ) 2 Se 2 with SrSe. Both Sr(Ag 1-x Li x ) 2 Se 2 and [Sr 3 Se 2 ][(Ag 1-x Li x ) 2 Se 2 ] exhibit a direct band gap, which increases with increasing Li substitution (x). Therefore, the band gap of Sr(Ag 1-x Li x ) 2 Se 2 can be precisely tuned via fine-tuning x that is controlled by only the flux ratio and temperature.

2D materials↗
DOE OSTI2021

Modification of Catalytic Properties of Hollandite Manganese Oxide by Ag Intercalation for Oxidative Acetalization of Ethanol to Diethoxyethane

The effect of addition of Ag to the catalytic properties of hollandite manganese oxide (HMO) was investigated for the oxidative acetalization of ethanol to diethoxyethane. Based on analysis with HRTEM, XRD, and EXAFS, Ag introduced onto HMO by deposition/precipitation was found to be present in different forms in the final catalyst depending on the calcination temperature. It could exist as nanoparticles on the outside surface of HMO nanorods for samples calcined at 60 °C, and as Ag atoms intercalated into the tunnels of the HMO structure for samples calcined at 500 °C. NH 3 desorption results showed that intercalation of Ag resulted in stronger Lewis acidic sites on HMO, which DFT computational results suggested to be due to Ag-induced electron redistribution in the HMO framework. Here, the intercalation of Ag atoms also made the HMO more easily reducible by lowering the H 2 reduction temperature from 500 to 200 °C. Consequently, the sample with intercalated Ag was more active for ethanol oxidation to acetaldehyde, achieving nearly 100% conversion of ethanol and acetaldehyde by 360 °C, and acetalization of acetaldehyde with ethanol to produce diethoxyethane selectively, resulting in 93.5% diethoxyethane yield, which was 10% higher than with samples containing Ag nanoparticles on HMO. This study demonstrated a little-studied phenomenon in which a metal alters the catalytic properties of an oxide electronically but not structurally and without direct participation in the reaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗