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NASA NTRS1975

Preferential concentration of certain elements in smaller aerosols emitted from aircraft engines

Aerosols from aircraft engines were collected with an eight-stage cascade sampler for a period of 24 h. The aerosol samples from each stage were analyzed for their elemental composition using the proton-induced X-ray emission (PIXE) technique. Seventeen elements (Si, P, S, Cl, K, Ca, Ti, V, Fe, Ni, Cu, Zn, Br, Sr, Nb, Sn, and Pb) were positively identified and quantitated at each stage. Six elements (S, Ca, Fe, Zn, Sn, and Pb) showed a fractional concentration increase with decreasing aerosol size. Similar, but less well-defined, trends were also observed for V and Ni. Silicon and chlorine, on the other hand, showed an opposite trend. Neutron-activation analysis of bulk aerosol samples collected every 2 h over the same period showed a correlation between concentration of Si, Ca, V, Ti, Zn, Br, and Sn and the density of air traffic at the airport. Analysis of the aviation-fuel samples by PIXE indicates that major fractions of Pb, Sn, Br, Zn, Ni, Fe, V, Ca, and S observed in these aerosol studies come from the aircraft engine exhaust.

Jolly, R. K.↗

DOE OSTI2024

Directed Flow and the Chiral Magnetic Effect in Ultrarelativistic Collisions with CMS at the LHC (Final Technical Report for DOE Grant # DE-SC0021080)

This Final Technical Report covers the years of activity for the Grant DE-SC0021080. It reflects the efforts of Alice Mignerey, the PI, Timothy Koeth, the co-PI, graduate students Eric Adams and Samuel Lascio, and undergraduates Alyssa Marinelli and Max Bernard. Results from three separate aspects of the project are presented: 1) understanding the radiation damage of the positive and negative sides of the Spectator Reaction Plane Detector (SRPD) for data from the 2018 PbPb run at the CERN LHC. 2) Results of the directed flow in PbPb collisions at √sN N = 5.02 TeV. 3) Activation studies of the sectors of the positive side of the SRPD and radiation damage studies on fused quartz using the Maryland 4-MeV electron accelerator. The most significant result is that the reaction plane derived directed flow for both participant and spectator reaction planes is many times larger than that obtained by ALICE.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Stable abnormal N-heterocyclic carbenes and their applications

Although N-heterocyclic carbenes (NHCs) have been known as ligands for organometallic complexes since the 1960s, these carbenes did not attract considerable attention until Arduengo et al. reported the isolation of a metal-free imidazol-2-ylidene in 1991. In 2001 Crabtree et al. reported a few complexes featuring an NHC isomer, namely an imidazol-5-ylidene, also termed abnormal NHC (aNHCs). In 2009, it was shown that providing to protect the C-2 position of an imidazolium salt, the deprotonation occurred at the C-5 position, affording imidazol-5-ylidenes that could be isolated. Over the last ten years, stable aNHCs have been used for designing a range of catalysts employing Pd(II), Cu(I), Ni(II), Fe(0), Zn(II), Ag(I), and Au(I/III) metal based precursors. These catalysts were utilized for different organic transformations such as the Suzuki–Miyaura cross-coupling reaction, C–H bond activation, dehydrogenative coupling, Huisgen 1,3-dipolar cycloaddition (click reaction), hydroheteroarylation, hydrosilylation reaction and migratory insertion of carbenes. Main-group metal complexes were also synthesized, including K(I), Al(III), Zn(II), Sn(II), Ge(II), and Si(II/IV). Among them, K(I), Al(III), and Zn(II) complexes were used for the polymerization of caprolactone and rac-lactide at room temperature. In addition, based on the superior nucleophilicity of aNHCs, relative to that of their nNHCs isomers, they were used for small molecules activation, such as carbon dioxide (CO 2 ), nitrous oxide (N 2 O), tetrahydrofuran (THF), tetrahydrothiophene and 9-borabicyclo[3.3.1]nonane (9BBN). aNHCs have also been shown to be efficient metal-free catalysts for ring opening polymerization of different cyclic esters at room temperature; they are among the most active metal-free catalysts for ε-caprolactone polymerization. Recently, aNHCs successfully accomplished the metal-free catalytic formylation of amides using CO 2 and the catalytic reduction of carbon dioxide, including atmospheric CO 2 , into methanol, under ambient conditions. Although other transition metal complexes featuring aNHCs as ligand have been prepared and used in catalysis, this review article summarize the results obtained with the isolated aNHCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1983

The non-Z-squared response of the heavy nuclei cosmic ray detector on HEAO-3

A combination of ion chambers and Cerenkov radiators similar to the Heavy Nuclei Experiment flown on HEAO-3 was calibrated at the Bevalac heavy-ion accelerator using beams of Mn-25 nuclei at kinetic energies up to about 1700 MeV/nucleon and Au-79 nuclei up to about 1000 MeV/nucleon. The data show only a small deviation (about 2-3 charge units at Au) from the Z-squared scaling used previously (Binns et al., 1981, 1982, 1983) to analyze the HNE data. Although at lower energy, the calibration indicates that the published relative abundances of the Sn-50/Ba-56 group and the published upper-limit actinide abundances are not likely to be significantly affected by non-Z-squared effects.

Garrard, T. L.↗

DOE OSTI2020

Materials Data on MnHg2C6(SN)6 by Materials Project

MnHg2C6(NS)6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Mn2+ sites. In the first Mn2+ site, Mn2+ is bonded in a distorted trigonal bipyramidal geometry to five N3- atoms. There are a spread of Mn–N bond distances ranging from 2.04–2.17 Å. In the second Mn2+ site, Mn2+ is bonded in an octahedral geometry to six N3- atoms. There are a spread of Mn–N bond distances ranging from 1.93–1.96 Å. There are four inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded to two equivalent N3- and three S2- atoms to form distorted HgS3N2 square pyramids that share a cornercorner with one HgS4 trigonal pyramid and an edgeedge with one HgS3N2 square pyramid. There are one shorter (2.55 Å) and one longer (2.98 Å) Hg–N bond lengths. There are a spread of Hg–S bond distances ranging from 2.48–3.00 Å. In the second Hg2+ site, Hg2+ is bonded in a distorted tetrahedral geometry to four S2- atoms. There are a spread of Hg–S bond distances ranging from 2.50–2.78 Å. In the third Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Hg–S bond distances ranging from 2.48–3.36 Å. In the fourth Hg2+ site, Hg2+ is bonded to four S2- atoms to form distorted corner-sharing HgS4 trigonal pyramids. There are a spread of Hg–S bond distances ranging from 2.57–2.81 Å. There are twelve inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.64 Å. In the second C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.17 Å. The C–S bond length is 1.65 Å. In the third C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the fourth C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the fifth C4+ site, C4+ is bonded in a linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.64 Å. In the sixth C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.62 Å. In the seventh C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the eighth C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the ninth C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the tenth C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. In the eleventh C4+ site, C4+ is bonded in a distorted single-bond geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.64 Å. In the twelfth C4+ site, C4+ is bonded in a distorted linear geometry to one N3- and one S2- atom. The C–N bond length is 1.18 Å. The C–S bond length is 1.65 Å. There are twelve inequivalent N3- sites. In the first N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the second N3- site, N3- is bonded in a distorted linear geometry to one Mn2+ and one C4+ atom. In the third N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the fourth N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the fifth N3- site, N3- is bonded in a bent 150 degrees geometry to one Mn2+ and one C4+ atom. In the sixth N3- site, N3- is bonded in a 1-coordinate geometry to two equivalent Hg2+ and one C4+ atom. In the seventh N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the eighth N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the ninth N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the tenth N3- site, N3- is bonded in a bent 150 degrees geometry to one Mn2+ and one C4+ atom. In the eleventh N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. In the twelfth N3- site, N3- is bonded in a linear geometry to one Mn2+ and one C4+ atom. There are twelve inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to two Hg2+ and one C4+ atom. In the second S2- site, S2- is bonded in a 3-coordinate geometry to two Hg2+ and one C4+ atom. In the third S2- site, S2- is bonded in an L-shaped geometry to one Hg2+ and one C4+ atom. In the fourth S2- site, S2- is bonded in a water-like geometry to one Hg2+ and one C4+ atom. In the fifth S2- site, S2- is bonded in a water-like geometry to one Hg2+ and one C4+ atom. In the sixth S2- site, S2- is bonded in a distorted trigonal non-coplanar geometry to two Hg2+ and one C4+ atom. In the seventh S2- site, S2- is bonded in a water-like geometry to one Hg2+ and one C4+ atom. In the eighth S2- site, S2- is bonded in an L-shaped geometry to one Hg2+ and one C4+ atom. In the ninth S2- site, S2- is bonded in a distorted water-like geometry to one Hg2+ and one C4+ atom. In the tenth S2- site, S2- is bonded in a 2-coordinate geometry to two Hg2+ and one C4+ atom. In the eleventh S2- site, S2- is bonded in an L-shaped geometry to one Hg2+ and one C4+ atom. In the twelfth S2- site, S2- is bonded in a water-like geometry to one Hg2+ and one C4+ atom.

36 MATERIALS SCIENCE↗

NASA NTRS1988

Ostwald ripening in a system with a high volume fraction of coarsening phase

The coarsening of Sn-rich and Pb-rich solid phases in contact with eutectic liquid in the volume fraction solid range above approximately 0.6, where the development of a solid skeletal structure inhibits sedimentation, is investigated. Particle intercept distributions are shown to be time independent when scaled by the average intercept. It is noted that the coarsening rate constants obtained exceed the values calculated from theory by factors ranging from about 2 to 5.

Hardy, S. C.↗

DOE OSTI2023

First Results From Nb3Sn Coatings of 2.6 GHz Nb SRF Cavities Using DC Cylindrical Magnetron Sputtering System

A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb3Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 °C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb3Sn phase and Nb (substrate). No peaks from any Nb- Sn compound other than Nb3Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 μm thick Nb3Sn. The first Nb3Sn coated cavity reached close to Eacc = 8 MV/m, demonstrating a quality factor Q0 of 3.2 × 108 at Tbath = 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q0 was close to 1.1 × 109, dominated by the residual resistance, at 2 K and Eacc = 5 MV/m. The Nb3Sn coated cavities demonstrated Tc in the range of 17.9 – 18 K. Here we present the commissioning experience, s ystem optimization, and the first results from the Nb3Sn fabrication on flat samples and SRF cavities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

FIRST RESULTS FROM Nb3Sn COATINGS OF 2.6 GHz Nb SRF CAVITIES USING DC CYLINDRICAL MAGNETRON SPUTTERING SYSTEM

A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb3Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 °C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb3Sn phase and Nb (substrate). No peaks from any Nb-Sn compound other than Nb3Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 µm thick Nb3Sn. The first Nb3Sn coated cavity reached close to Eacc = 8 MV/m, demonstrating a quality factor Q0 of 3.2 × 108 at Tbath = 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q0 was close to 1.1 × 109, dominated by the residual resistance, at 2 K and Eacc = 5 MV/m. The Nb3Sn coated cavities demonstrated Tc in the range of 17.9 ? 18 K. Here, we present the commissioning experience, system optimization, and the first results from the Nb3Sn fabrication on flat samples and SRF cavities.

Shakel, M.S.↗

DOE OSTI2023

FIRST RESULTS FROM Nb3Sn COATINGS OF 2.6 GHz Nb SRF CAVITIES USING DC CYLINDRICAL MAGNETRON SPUTTERING SYSTEM

A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb3Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 °C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb3Sn phase and Nb (substrate). No peaks from any Nb-Sn compound other than Nb3Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 µm thick Nb3Sn. The first Nb3Sn coated cavity reached close to Eacc = 8 MV/m, demonstrating a quality factor Q0 of 3.2 × 108 at Tbath = 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q0 was close to 1.1 × 109, dominated by the residual resistance, at 2 K and Eacc = 5 MV/m. The Nb3Sn coated cavities demonstrated Tc in the range of 17.9 ? 18 K. Here, we present the commissioning experience, system optimization, and the first results from the Nb3Sn fabrication on flat samples and SRF cavities.

Shakel, M. S.↗

DOE OSTI2021

Efficient Screening of Bi–Metallic Electrocatalysts for Glycerol Valorization

Glycerol is a byproduct of biodiesel production and, as such, it is of limited economic value. By means of electrooxidation, glycerol can be used as a feedstock for scalable hydrogen production, in addition to conversion to value-added products. The development of novel and efficient catalytic electrode materials for the anodic side of the reaction is a key towards a hydrogen-based energy economy. In the present study, a computational screening protocol combining DFT, scaling relations, and microkinetic modeling allows for a rational selection of novel catalysts that can deliver efficient glycerol electrooxidation, low cost of production, and environmental sustainability. Activity and chemical selectivity towards hydrogen production on pure metal catalysts is discussed in terms of volcano-shaped plots. We find that the selectivity in the glycerol oxidation reaction is influenced by a different energy landscape when in the presence of water and best classified by a comparison of O—H and C—H bond-breaking barriers. In addition, we screened 3570 bi-metallic catalysts in the AB (L1 0 ) and A 3 B (L1 2 ) ordered structures for activity, stability, price, and toxicity. By filtering based on the criteria for toxicity, resistance to oxidation, miscibility, and price, we have identified 5 L1 0 structured catalysts (AgPd, AuPd, PtSb, CuPt, and AgPt) and 20 L1 2 catalysts (Ga 3 Ta, In 3 Ta, Ir 3 W, Ir 3 Mo, Cu 3 Pt, Ir 3 Ta, Ir 3 Re, Pd 3 Bi, Pd 3 Cu, Pd 3 W, Pd 3 Co, Pd 3 Sn, Pd 3 Mo, Pd 3 Ag, Pd 3 Ga, Pd 3 Ta, Au 3 Ru, Pd 3 In, Au 3 Ir, and Pd 3 Au) that are all predicted to show high activity. We also identify an additional 37 L1 0 and 92 L1 2 structured electrocatalysts with an anticipated medium-high activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

First β-decay spectroscopy of 135 In and new β-decay branches of 134 In

The β decay of the neutron-rich 134 In and 135 In was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z=50 above the N=82 shell. The β-delayed γ-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three β-decay branches of 134 In were established, two of which were observed for the first time. Population of neutron-unbound states decaying via γ rays was identified in the two daughter nuclei of 134 In, 134 Sn and 133 Sn, at excitation energies exceeding the neutron separation energy by 1 MeV. The β-delayed one- and two-neutron emission branching ratios of 134 In were determined and compared with theoretical calculations. The β-delayed one-neutron decay was observed to be dominant β-decay branch of 134 In even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of 134 Sn. Transitions following the β decay of 135 In are reported for the first time, including γ rays tentatively attributed to 135 Sn. In total, six new levels were identified in 134 Sn on the basis of the βγγ coincidences observed in the 134 In and 135 Inβ decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2 + state in 133 Sn was observed in both β decays and its assignment is discussed. Experimental level schemes of 134 Sn and 135 Sn are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2 + , 4 + , and 6 + levels in 134 Sn were determined. From the lifetime of the 4 + state measured for the first time, an unexpectedly large B(E2;4 + → 2 + ) transition strength was deduced, which is not reproduced by the shell-model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2023

First Results From Nb3Sn Coatings of 2.6 GHz Nb SRF Cavities Using DC Cylindrical Magnetron Sputtering System

A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb3Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950°C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb3Sn phase and Nb (substrate). No peaks from any Nb- Sn compound other than Nb3Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 μm thick Nb3Sn. The first Nb3Sn coated cavity reached close to Eacc = 8 MV/m, demonstrating a quality factor Q0 of $3.2 \times 108$ at Tbath = 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q0 was close to $1.1 \times 109$, dominated by the residual resistance, at 2 K and Eacc = 5 MV/m. The Nb3Sn coated cavities demonstrated Tc in the range of $17.9 -- 18$ K. Here we present the commissioning experience, system optimization, and the first results from the Nb3Sn fabrication on flat samples and SRF cavities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS2006

"Suzaku Highlight Results on Supernova Remnants"

Highlights of the early Suzaku (formerly Astro-E2) observations of supernova remnants are presented. Suzaku offers unique capabilities for the study of supernova remnants. The unprecedented combination of imaging and spectral resolution below 1 keV in the X-ray Imaging Spectrometer (XIS) makes possible mapping of C, N and O abundances in Galactic remnants of all ages. The first detection of carbon lines in the Cygnus Loop and mapping of the O VII to O VIII ratio in SN 1006 demonstrate this capability. The XIS sensitivity to soft, low surface brightness emission is exemplified by spectroscopy in the 0.3-1.0 keV band of the North Polar Spur and other Galactic ISM structures. Such observations make possible inferences about plasma conditions and abundances. The sensitivity above 6 keV via a combination of the XIS (below 10 keV) and the Hard X-ray Detector (above 10 keV) allows broad band (2-40 keV) spectroscopy and mapping of extended remnants with hard emission components. These components are generally associated with sites of particle acceleration, and measuring their spectral shape potentially provides information about the TeV electron population and its acceleration and energy loss mechanisms. Examples of such remnants observed by Suzaku are the non-thermal emission dominated remnants RX J1713.7-3946 and RX J0852.0-4622, for which flux beyond 30 keV has been detected. The status of the mission and prospects for future groundbreaking observations of supernova remnants will be discussed.

Petre, Robert↗

DOE OSTI2023

Softening of a flat phonon mode in the kagome ScV 6 Sn 6

Geometrically frustrated kagome lattices are raising as novel platforms to engineer correlated topological electron flat bands that are prominent to electronic instabilities. Here, we demonstrate a phonon softening at the k z = π plane in ScV 6 Sn 6 . The low energy longitudinal phonon collapses at ~98 K and q = $\tfrac{1}{3}$ $\tfrac{1}{3}$ $\tfrac{1}{2}$ due to the electron-phonon interaction, without the emergence of long-range charge order which sets in at a different propagation vector q CDW = $\tfrac{1}{3}$ $\tfrac{1}{3}$ $\tfrac{1}{3}$. Theoretical calculations corroborate the experimental finding to indicate that the leading instability is located at $\tfrac{1}{3}$ $\tfrac{1}{3}$ $\tfrac{1}{2}$ of a rather flat mode. We relate the phonon renormalization to the orbital-resolved susceptibility of the trigonal Sn atoms and explain the approximately flat phonon dispersion. Our data report the first example of the collapse of a kagome bosonic mode and promote the 166 compounds of kagomes as primary candidates to explore correlated flat phonon-topological flat electron physics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

High current density electroreduction of CO 2 into formate with tin oxide nanospheres

In this study, we demonstrate three-dimensional (3D) hollow nanosphere electrocatalysts for CO 2 conversion into formate with excellent H-Cell performance and industrially-relevant current density in a 25 cm 2 membrane electrode assembly electrolyzer device. Varying calcination temperature maximized formate production via optimizing the crystallinity and particle size of the constituent SnO 2 nanoparticles. The best performing SnO 2 nanosphere catalysts contained ~ 7.5 nm nanocrystals and produced 71–81% formate Faradaic efficiency (FE) between -0.9 V and -1.3 V vs. the reversible hydrogen electrode (RHE) at a maximum formate partial current density of 73 ± 2 mA cm geo -2 at -1.3 V vs. RHE. The higher performance of nanosphere catalysts over SnO 2 nanoparticles and commercially-available catalyst could be ascribed to their initial structure providing higher electrochemical surface area and preventing extensive nanocrystal growth during CO 2 reduction. Our results are among the highest performance reported for SnO 2 electrocatalysts in aqueous H-cells. We observed an average 68 ± 8% FE over 35 h of operation with multiple on/off cycles. In situ Raman and time-dependent X-ray diffraction measurements identified metallic Sn as electrocatalytic active sites during long-term operation. Further evaluation in a 25 cm 2 electrolyzer cell demonstrated impressive performance with a sustained current density of 500 mA cm geo -2 and an average 75 ± 6% formate FE over 24 h of operation. Our results provide additional design concepts for boosting the performance of formate-producing catalysts.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Optical polarization and spectral properties of the hydrogen-poor superluminous supernovae SN 2021bnw and SN 2021fpl

ABSTRACT New optical photometric, spectroscopic, and imaging polarimetry data are combined with publicly available data to study some of the physical properties of the two hydrogen-poor superluminous supernovae (SLSNe) SN 2021bnw and SN 2021fpl. For each SLSN, the best-fitting parameters obtained from the magnetar model with Modular Open-Source Fitter for Transients do not depart from the range of parameter obtained on other SLSNe discussed in the literature. A spectral analysis with SYN++ shows that SN 2021bnw is a W type, fast evolver, while SN 2021fpl is a 15bn type, slow evolver. The analysis of the polarimetry data obtained on SN 2021fpl at four epochs (+1.8, +20.6, +34.1, and +43.0 d, rest frame) shows >3σ polarization detections in the range of 0.8–1 per cent. A comparison of the spectroscopy data suggests that SN 2021fpl underwent a spectral transition a bit earlier than SN 2015bn, during which, similarly, it could have underwent a polarization transition. The analysis of the polarimetry data obtained on SN 2021bnw does not show any departure from symmetry of the photosphere at an empirical diffusion time-scale of ≈2 (+81.1 d rest frame). This result is consistent with those on the sample of W-type SLSN observed at empirical diffusion time-scale ≤ 1 with that technique, even though it is not clear the effect of limited spectral windows varying from one object to the other. Measurements at higher empirical diffusion time-scale may be needed to see any departure from symmetry as it is discussed in the literature for SN 2017egm.

Astronomy & Astrophysics↗

DOE OSTI2023

First Results from Nb3Sn Coatings of 2.6 GHz Nb SRF Cavities Using DC Cylindrical Magnetron Sputtering System

A DC cylindrical magnetron sputtering system has been commissioned and operated to deposit Nb3Sn onto 2.6 GHz Nb SRF cavities. After optimizing the deposition conditions in a mock-up cavity, Nb-Sn films are deposited first on flat samples by multilayer sequential sputtering of Nb and Sn, and later annealed at 950 {\deg}C for 3 hours. X-ray diffraction of the films showed multiple peaks for the Nb3Sn phase and Nb (substrate). No peaks from any Nb3Sn compound other than Nb3Sn were detected. Later three 2.6 GHz Nb SRF cavities are coated with ~1 $\mu$m thick Nb3Sn. The first Nb3Sn coated cavity reached close to Eacc = 8 MV/m, demonstrating a quality factor Q0 of 3.2 x 108 at Tbath = 4.4 K and Eacc = 5 MV/m, about a factor of three higher than that of Nb at this temperature. Q0 was close to 1.1 x 109, dominated by the residual resistance, at 2 K and Eacc = 5 MV/m. The Nb3Sn coated cavities demonstrated Tc in the range of 17.9 - 18 K. Here we present the commissioning experience, system optimization, and the first results from the Nb3Sn fabrication on flat samples and SRF cavities.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Magnetic ordering in Eu 2 In and Eu 2 Sn

Eu 2 In and Eu 2 Sn crystallize in the orthorhombic Co 2 Si-type structure (oP12, Pnma, No. 62) with In and Sn atoms occupying one 4c site and the Eu atoms filling two other 4c sites. Eu 2 In has a nearly ideal first-order magnetostructural transition (FOMT) at 55 K with a hysteresis of less than 0.1 K, a large entropy change and an adiabatic temperature change of 5.0 K in a field of 2 T. The anhysteretic nature of the FOMT is likely due to there being no change in cell symmetry and relatively small changes in the lattice parameters. There is no magnetostructural transition in Eu2Sn. In this work we present the results of powder neutron diffraction, magnetization, and Eu Mössbauer spectroscopy aimed to investigate the nature of magnetic order for both Eu 2 In and Eu 2 Sn. The Eu Mössbauer spectrum of Eu 2 In at 5 K shows two equal area components, consistent with Eu occupying two equal multiplicity crystallographic sites. However, the different hyperfine fields (B) of 27 T and 17 T suggest that the magnetic environments of the Eu moments on the two 4c sites are different. Neutron diffraction data at 2.5 K show that in Eu 2 In the order is ferromagnetic, with Eu moments on both Eu sites oriented parallel to the a-axis; moment values of 6.8 μB and 6.5 μB were found. For Eu 2 Sn measurements find two antiferromagnetic transitions, which are corroborated by neutron diffraction. Analysis of density-functional theory calculations shows negligible energy difference between differing magnetic configurations, indirectly supporting stability of multiple magnetic structures observed experimentally. While the transition at T N1 = 30 K corresponds to the formation of a simple k 1 = 0 antiferromagnetic structure with Eu-moments pointing along the b-axis, at T N2 = 13 K a coexisting second magnetic order with k 2 = [0, ½, ½] appears.

36 MATERIALS SCIENCE↗