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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Control of wetting and uniformity via ZrSi x formation in ceramic-to-metal joints fabricated using Ag-Zr brazes

The deposition of a 2.0 µm SiO 2 film on the alumina surface in Kovar TM /94% alumina joints enables the formation of a silicide reaction layer on the alumina during brazing with 97Ag2Zr1Cu. Additionally, the average and standard deviation of joint thickness decrease from 50 to 15 and 29 to 4 µm, respectively compared to joints without added SiO 2 . Finally, the average failure stress of these braze joints was 45 MPa, while that of similar joints without added SiO 2 was 90 MPa. Sessile drop experiments of 98Ag2Zr on SiO 2 and 99.6% Al 2 O 3 substrates show that the braze wets and spreads to 3x its original area on SiO 2 with a wetting angle near 0°, but remains the same area on 99.6% Al 2 O 3 with a wetting angle of 106.6°. Focused-ion-beam scanning electron microscopy analysis of a cross-section of the 98Ag2Zr sessile drop on the SiO 2 substrate has shown that Zr reacts with SiO 2 to form Zr oxide and silicide layers. Scanning transmission electron microscopy diffraction and energy dispersive X-ray spectroscopy analysis indicate this silicide layer contains tetragonal Zr 5 Si 4 . In conclusion, analysis shows the silicide layer enhances wetting and joint uniformity while unreacted SiO 2 embrittles the joint and degrades strength.

alumina↗
DOE OSTI2024

Predictive Models and Novel Accelerated Tests for the Reliability of Cell Metallization in Photovoltaic Modules (Final Report)

Studies of metallization corrosion m photovoltaics have mainly been limited to comparisons of modules placed in accelerated chambers to fielded modules [1]. Damp Heat accelerated tests and phenomenological equations [2] are used to assess metallization corrosion without understanding the effect of UV light and temperature and humidity cycles on encapsulant adhesion degradation. The roles of encapsulant in-and out-diffusions of moisture and encapsulant impurities are important. Furthermore, few photovoltaic metallization corrosion studies included the role of bias and leakage currents, which are crucial in the electrochemical reaction of metallization. Leakage currents can highly accelerate the corrosion mechanism and are important to include in the studies of corrosion. In our research plan, we will address the following gaps in the PV community's understanding of metallization corrosion: (1) metallization corrosion with bias, humidity, and impurities in the encapsulant or metallization; (2) humidity diffusion through fresh and degraded encapsulants; and (3) comparison of model predictions with outdoor field modules and SunPower's extensive data for its back-contact and front-contact fleets [2] along with NREL's store of >20 year old modules. Our goal is to build models and accelerated tests to predict long term degradation of metallization corrosion of photovoltaic modules in the field. Our studies will include metals used in c-Si solar cells (Cu, Ag, and Al) and commonly used encapsulants (EV A (ethylene vinyl acetate), TPO (thermoplastic olefin), and silicone).

14 SOLAR ENERGY↗
DOE OSTI2024

Heterometallic UO 2 2+ /Ag + Complexes: Structural Design and Luminescence Properties

Reported here are the synthesis, structural characterization, and luminescence properties of 11 novel UO 2 2+ /Ag + heterometallic complexes. Halogenated benzoic acids (2,6-dihalobenzoic acid (halo = F, Br), 3,5-dichlorobenzoic acid, and 3-halobenzoic acid (halo = Br, I)) and N-donor polycyclic ligands (2,2′-bipyridine, 2,2’;6′,2″-terpyridine, 1,10-phenanthroline, 2,2′-bipyrimidine) were employed to synthesize a set of compounds and induce structural diversity. The primary mode of coordination with the uranyl cation is hexagonal bipyramidal monomeric units with three halobenzoate ligands in the equatorial plane, though 1-D chains with pentagonal bipyramidal uranyl centers also form. The Ag + cations coordinate preferentially to the N-donor ligands and serve as counter-cations for the anionic uranyl motifs. The soft ligand character of the N-donor molecules is found to be a requirement for the inclusion of the Ag + cation into the structures. Anionic uranyl units and cationic silver units assemble via noncovalent interactions between π systems on adjacent rings and between halogens (when Br and I are present). Solid-state emission spectra display the usual uranyl band with superimposed vibronic fine structure, except for that of compound 1 , which shows emission from the 2,2′-bipyridine center. This family of compounds represents a substantial contribution to the already rich library of UO 2 2+ /Ag + compounds, and the synthetic parameters discussed within reveal a platform for the design of new heterometallic uranyl-containing materials.

anions↗
DOE OSTI2025

Dual-Bed Radioiodine Capture from Complex Gas Streams with Zeolites: Regeneration and Reuse of Primary Sorbent Beds for Sustainable Waste Management

Dual-sorbent systems are proposed for radioiodine management with a regenerated primary bed for multiple cycles of use in complex conditions and a secondary bed for disposal with higher waste loadings. Sorbent approaches for the effective capture of gaseous radioiodine (isotopes 129 I and 131 I) produced from a range of nuclear processes have been studied for over half a century. (1−5) Whether or not a sorbent (e.g., molecular sieve) is required to physically screen/trap or chemically bind a radionuclide of interest through chemisorption, the complexity of the gas stream has a large impact on the performance (e.g., loading capacity, selectivity) and active life of a sorbent bed. (3) Silver mordenite (AgZ), the U.S. Department of Energy baseline sorbent for radioiodine capture from nuclear processes, performs well within acidic conditions and at elevated temperatures (6) and can be consolidated into a chemically durable waste form for long-term disposal. (7,8) However, new sorbents are being sought because optimal capture performance of AgZ significantly decreases in dynamic oxidizing environments with competing species, and it is expensive and it contains Ag (a toxic metal). (9) Until a new sorbent is found to replace AgZ, the regeneration and reuse of AgZ is an attractive alternative to a single-use primary sorbent bed. In this regard, a primary sorbent could be designed for enhanced capture in complex gas streams and the ability to be regenerated for reuse. Here, a secondary sorbent could then be tailored for maximum iodine loading in the gas stream and chemical durability within a disposal facility.

chemisorption↗
DOE OSTI2020

Materials Data on U3Ag2(GeO8)2 by Materials Project

U3Ag2(GeO8)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are three inequivalent U6+ sites. In the first U6+ site, U6+ is bonded to seven O2- atoms to form distorted UO7 pentagonal bipyramids that share corners with four equivalent AgO7 pentagonal bipyramids, corners with two equivalent GeO5 trigonal bipyramids, edges with two equivalent UO7 pentagonal bipyramids, and edges with two equivalent GeO5 trigonal bipyramids. There are a spread of U–O bond distances ranging from 1.86–2.52 Å. In the second U6+ site, U6+ is bonded to seven O2- atoms to form distorted UO7 pentagonal bipyramids that share corners with four equivalent AgO7 pentagonal bipyramids, corners with two equivalent GeO5 trigonal bipyramids, and edges with two equivalent GeO5 trigonal bipyramids. There are a spread of U–O bond distances ranging from 1.86–2.40 Å. In the third U6+ site, U6+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of U–O bond distances ranging from 1.85–2.31 Å. Ag3+ is bonded to seven O2- atoms to form distorted AgO7 pentagonal bipyramids that share corners with four UO7 pentagonal bipyramids and faces with two equivalent AgO7 pentagonal bipyramids. There are a spread of Ag–O bond distances ranging from 2.52–2.75 Å. Ge4+ is bonded to five O2- atoms to form GeO5 trigonal bipyramids that share corners with two UO7 pentagonal bipyramids, corners with two equivalent GeO5 trigonal bipyramids, and edges with two UO7 pentagonal bipyramids. There are a spread of Ge–O bond distances ranging from 1.80–1.97 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one U6+ and two equivalent Ag3+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two U6+ and one Ge4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent U6+ and one Ge4+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one U6+ and two equivalent Ge4+ atoms. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to one U6+ and two equivalent Ge4+ atoms. In the sixth O2- site, O2- is bonded in a single-bond geometry to one U6+ and two equivalent Ag3+ atoms. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to one U6+ and two equivalent Ag3+ atoms. In the eighth O2- site, O2- is bonded in a distorted single-bond geometry to one U6+ and two equivalent Ag3+ atoms. In the ninth O2- site, O2- is bonded in a distorted single-bond geometry to one U6+ and two equivalent Ag3+ atoms. In the tenth O2- site, O2- is bonded in a bent 120 degrees geometry to one Ag3+ and one O2- atom. The O–O bond length is 1.24 Å. In the eleventh O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two U6+ and one Ge4+ atom. In the twelfth O2- site, O2- is bonded in a distorted single-bond geometry to one U6+ and two equivalent Ag3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Degradation of Monocrystalline Silicon Photovoltaic Modules From a 10-Year-Old Rooftop System in Florida

A system of 180 monocrystalline aluminum back-surface field modules were installed in Cocoa, Florida, for 10 years. In total, 156 modules are characterized and compared to 3 controls. Power degradation rates vary between – 0.14% to – 3.22% per year, with median and average rates of –0.92% and –1.05% per year, respectively. The losses are primarily resistive with minor optical and recombination loss contributions. Electroluminescence imaging shows a characteristic pattern, which is shown to be resistive in nature when compared to photoluminescence. Resistive losses are due to corrosion of the rear contact Ag/solder interface and, to a much lesser degree, gridline Ag oxidation. Moisture ingress through the backsheet is likely responsible for mediating corrosion. Optical losses are due mostly to a combination of antireflection coating degradation, minor encapsulant browning, and delamination. Minor front contact corrosion may contribute to recombination. Furthermore, this study expands upon previous work on this vintage of the module by examining a large sample set, comprehensive characterization including techniques not previously used on these modules, and a comparison between two other systems of different climates.

14 SOLAR ENERGY↗
NASA NTRS1983

Results of apparent atomic oxygen reactions on Ag, C, and Os exposed during the Shuttle STS-4 orbits

Films selected for anticipated reaction with atomic oxygen, namely carbon, silver, and osmium, were exposed during the Shuttle STS-4 mission. A silver film within 5 nm of 225 nm thick was converted to a transparent blue-green interference film within 5 nm of 355 nm thick. Both carbon and osmium films 10-30 nm thick apparently formed volatile oxides and disappeared, except where well shielded. A calculated total of approximately 7 x 10 to the 19th oxygen atoms per sq cm struck the surfaces, which could have removed on the order of 3 microns of material if only 10 percent reacted. The absence of apparent effects on adjacent thin and thick gold films is offered as evidence that sputtering is not responsible.

Peters, P. N.↗
DOE OSTI2020

Materials Data on AgBi(PS3)2 by Materials Project

AgBi(PS3)2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one AgBi(PS3)2 sheet oriented in the (0, 1, -1) direction. Ag1+ is bonded in a 4-coordinate geometry to four S2- atoms. There are a spread of Ag–S bond distances ranging from 2.53–2.78 Å. Bi1+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Bi–S bond distances ranging from 2.79–3.14 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are one shorter (2.01 Å) and two longer (2.06 Å) P–S bond lengths. In the second P5+ site, P5+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 2.02–2.09 Å. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to one Ag1+, one Bi1+, and one P5+ atom. In the second S2- site, S2- is bonded in a water-like geometry to one Ag1+ and one P5+ atom. In the third S2- site, S2- is bonded in a 1-coordinate geometry to one Bi1+ and one P5+ atom. In the fourth S2- site, S2- is bonded in a 1-coordinate geometry to two equivalent Bi1+ and one P5+ atom. In the fifth S2- site, S2- is bonded in a distorted trigonal non-coplanar geometry to one Ag1+, one Bi1+, and one P5+ atom. In the sixth S2- site, S2- is bonded in a 1-coordinate geometry to one Ag1+, one Bi1+, and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgH5S2O9 by Materials Project

AgH5S2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ag1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ag–O bond distances ranging from 2.41–2.79 Å. There are five inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.52 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.55 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.60 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.59 Å) H–O bond length. In the fifth H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.63 Å) H–O bond length. There are two inequivalent S6+ sites. In the first S6+ site, S6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of S–O bond distances ranging from 1.46–1.57 Å. In the second S6+ site, S6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of S–O bond distances ranging from 1.45–1.58 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one Ag1+ and one S6+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one H1+ and one S6+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ag1+, one H1+, and one S6+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ag1+ and one S6+ atom. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to two H1+ and one S6+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Ag1+, one H1+, and one S6+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Ag1+, one H1+, and one S6+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ag1+, one H1+, and one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Single Crystal Growth of Synthetic Sulfide- and Phosphide-Based Minerals for Physical Measurements

In this work, we review recent advances in the use of high-temperature solution growth that allow for the growth of single crystalline samples of synthetic minerals. We outline how low-melting binary or ternary solutions are attractive solvents for solution growth and provide examples of the growth of bismuthinite (Bi 2 S 3 ), galena (PbS) and parkerite (Ni 3 Bi 2 S 2 ). We then focus on the Rh-S, Pd-S and Ni-P phase spaces to discuss how the low-melting regions near transition metal-main group eutectic compositions make excellent solvents for crystal growth of several binary and ternary minerals containing both high melting and volatile elements as well as for the discovery of new materials. We end by discussing the growth of synthetic canfieldite (Ag 8 SnS 6 ) and argyrodite (Ag 8 GeS 6 ) from Ag 2 S–Sn-S-based solutions.

58 GEOSCIENCES↗
DOE OSTI2021

Organic Hole Transport Material Ionization Potential Dictates Diffusion Kinetics of Iodine Species in Halide Perovskite Devices

Iodine-containing volatiles are major degradation products of halide perovskite materials under irradiation, yet iodine diffusion kinetics into and throughout organic hole transport materials (HTMs) and consequent reactions are largely unexplored. In this work, we modify the Ca:O 2 corrosion test to Ag:I 2 to quantify I 2 transmission rates through common organic HTMs. We observe I 2 permeability to inversely correlate with HTM ionization energy, or the highest occupied molecular orbital (HOMO) energy. Tracking electronic conductance during exposure to I 2 confirms shallow HOMO HTMs are strongly oxidized (i.e., doped), leading to substantial I 2 uptake and increased transmission rates. Finally, relationships between HOMO level, doping, and transmission rate are maintained when methylammonium lead triiodide (MAPbI 3 ) photolysis products are the only source of iodine. While HTM energetics influence the initial performance of halide perovskite devices by selective charge extraction, our results further suggest they will affect device stability; deeper HOMO energy HTMs will suppress iodine migration and associated degradation mechanisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Thermal energy transport in laser-driven high x-ray conversion efficiency metallic silver nanowire foams

Here, we report on record brightness from Ag x-ray emission obtained using a novel laser-produced plasma source. The reported K-shell conversion efficiency of nearly 1% with a radiant energy of ≈ 0.6 kJ/sr from Ag ions is the highest presently recorded and is about twofold greater than more conventional metal-lined cavity targets. He-like Ag ions are the dominant radiators at ≈ 22.7 keV, which contrast the x-ray sources from other pulse power facilities that produce K-shell x-rays from Auger processes in near-neutral ions driven by the nonthermal hot electrons produced in the Z-pinch implosion. The reported x-ray emission was produced from a 4-mm-diameter, 4-mm-long underdense silver nanowire target at 10⁢ mg/⁢cm 3 . The National Ignition Facility laser beams deposited ≈ 1000 kJ of 3ω light into the target with a ≈ 400 TW, 2.5 ns square pulse. Finally, we show via comparisons of data with radiation-hydrodynamics simulations that flux-limited classical thermal energy transport models are inadequate in correctly modeling the behavior of these non-local thermodynamic equilibrium plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Materials Data on Ag7P3S11 by Materials Project

Ag7P3S11 is Chalcostibite-like structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are seven inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded in a 4-coordinate geometry to four S2- atoms. There are a spread of Ag–S bond distances ranging from 2.57–3.16 Å. In the second Ag1+ site, Ag1+ is bonded to four S2- atoms to form distorted AgS4 trigonal pyramids that share corners with four PS4 tetrahedra. There are a spread of Ag–S bond distances ranging from 2.56–2.69 Å. In the third Ag1+ site, Ag1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Ag–S bond distances ranging from 2.55–3.16 Å. In the fourth Ag1+ site, Ag1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Ag–S bond distances ranging from 2.48–3.22 Å. In the fifth Ag1+ site, Ag1+ is bonded in a 4-coordinate geometry to four S2- atoms. There are a spread of Ag–S bond distances ranging from 2.55–2.72 Å. In the sixth Ag1+ site, Ag1+ is bonded to four S2- atoms to form AgS4 tetrahedra that share corners with four PS4 tetrahedra. There are a spread of Ag–S bond distances ranging from 2.57–2.63 Å. In the seventh Ag1+ site, Ag1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Ag–S bond distances ranging from 2.56–3.22 Å. There are three inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share a cornercorner with one AgS4 tetrahedra, a cornercorner with one PS4 tetrahedra, and a cornercorner with one AgS4 trigonal pyramid. There are a spread of P–S bond distances ranging from 2.03–2.14 Å. In the second P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share corners with three equivalent AgS4 tetrahedra and a cornercorner with one AgS4 trigonal pyramid. There are a spread of P–S bond distances ranging from 2.04–2.10 Å. In the third P5+ site, P5+ is bonded to four S2- atoms to form PS4 tetrahedra that share a cornercorner with one PS4 tetrahedra and corners with two equivalent AgS4 trigonal pyramids. There are a spread of P–S bond distances ranging from 2.01–2.17 Å. There are eleven inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to three Ag1+ and one P5+ atom. In the second S2- site, S2- is bonded to three Ag1+ and one P5+ atom to form corner-sharing SAg3P tetrahedra. In the third S2- site, S2- is bonded in a distorted bent 120 degrees geometry to two P5+ atoms. In the fourth S2- site, S2- is bonded in a 3-coordinate geometry to three Ag1+ and one P5+ atom. In the fifth S2- site, S2- is bonded in a 4-coordinate geometry to three Ag1+ and one P5+ atom. In the sixth S2- site, S2- is bonded in a 4-coordinate geometry to three Ag1+ and one P5+ atom. In the seventh S2- site, S2- is bonded in a distorted trigonal non-coplanar geometry to two Ag1+ and one P5+ atom. In the eighth S2- site, S2- is bonded in a 3-coordinate geometry to four Ag1+ and one P5+ atom. In the ninth S2- site, S2- is bonded in a 4-coordinate geometry to three Ag1+ and one P5+ atom. In the tenth S2- site, S2- is bonded to three Ag1+ and one P5+ atom to form corner-sharing SAg3P tetrahedra. In the eleventh S2- site, S2- is bonded in a 5-coordinate geometry to four Ag1+ and one P5+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2003

The NASA Smart Probe Project for real-time multiple microsensor tissue recognition

BACKGROUND: Remote surgery requires automated sensors, effectors and sensor-effector communication. The NASA Smart Probe Project has focused on the sensor aspect. METHODS: The NASA Smart Probe uses neural networks and data from multiple microsensors for a unique tissue signature in real time. Animal and human trials use several probe configurations: (1) 8-microsensor probe (2.5 mm in diameter) for rodent studies (normal and subcutaneous mammary tumor tissues), and (2) 21-gauge needle probe with 3 spectroscopic fibers and an impedance microelectrode for breast cancer diagnosis in humans. Multisensor data are collected in real time (update 100 times/s) using PCs. RESULTS: Human data (collected by NASA licensee BioLuminate) from 15 women undergoing breast biopsy distinguished normal tissue from both benign tumors and breast carcinoma. Tumor margins and necrosis are rapidly detected. CONCLUSION: Real-time tissue identification is achievable. Potential applications, including probes incorporating nanoelectrode arrays, are presented. Copyright 2003 S. Karger AG, Basel.

Biopsy/methods↗
DOE OSTI2023

Dust from evolved stars: a pilot analysis of the AGB to PN transition

ABSTRACT We present a novel approach to address dust production by low- and intermediate-mass stars. We study the asymptotic giant branch (AGB) phase, during which the formation of dust takes place, from the perspective of post-AGB and planetary nebula (PN) evolutionary stage. Using results from stellar evolution and dust formation modelling, we interpret the spectral energy distribution of carbon-dust-rich sources currently evolving through different evolutionary phases, believed to descend from progenitors of similar mass and chemical composition. Comparing the results of different stages along the AGB to PNe transition, we can provide distinct insights on the amount of dust and gas released during the very late AGB phases. While the post-AGB traces the history of dust production back to the tip of the AGB phase, investigating the PNe is important to reconstruct the mass-loss process experienced after the last thermal pulse. The dust surrounding the post-AGB was formed soon after the tip of the AGB. The PNe dust-to-gas ratio is ∼10−3, 2.5 times smaller than what expected for the same initial mass star during the last AGB interpulse, possibly suggesting that dust might be destroyed during the PN phase. Measuring the amount of dust present in the nebula can constrain the capacity of the dust to survive the central star heating.

Dell’Agli, F. (ORCID:0000000324426981)↗
DOE OSTI2020

Origin of Large Meteoritic SiC Stardust Grains in Metal-rich AGB Stars

Stardust grains that originated in ancient stars and supernovae are recovered from meteorites and carry the detailed composition of their astronomical sites of origin. We present evidence that the majority of large (μm-sized) meteoritic silicon carbide (SiC) grains formed in C-rich asymptotic giant branch (AGB) stars that were more metal-rich than the Sun. In the framework of the slow neutron captures (the s process) that occur in AGB stars, the lower-than-solar $^{88}$Sr/$^{86}$Sr isotopic ratios measured in the large SiC grains can only be accompanied by Ce/Y elemental ratios that are also lower than solar and predominately observed in metal-rich barium stars—the binary companions of AGB stars. Such an origin suggests that these large grains represent the material from high-metallicity AGB stars needed to explain the s-process nucleosynthesis variations observed in bulk meteorites. In the outflows of metal-rich, C-rich AGB stars, SiC grains are predicted to be small (≃0.2 μm); large (≃μm-sized) SiC grains can grow if the number of dust seeds is 2–3 orders of magnitude lower than the standard value of 10 -13 times the number of H atoms. We therefore predict that with increasing metallicity, the number of dust seeds might decrease, resulting in the production of larger SiC grains.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Suppressing Charged Cation Antisites via Se Vapor Annealing Enables p-Type Dopability in AgBiSe 2 –SnSe Thermoelectrics

Cation disordering is commonly found in multinary cubic compounds, but its effect on electronic properties has been neglected because of difficulties in determining the ordered structure and defect energetics. An absence of rational understanding of the point defects present has led to poor reproducibility and uncontrolled conduction type. AgBiSe 2 is a representative compound that suffers from poor reproducibility of thermoelectric properties, while the origins of its intrinsic n-type conductivity remain speculative. Here, it is demonstrated that cation disordering is facilitated by Bi Ag charged antisite defects in cubic AgBiSe 2 which also act as a principal donor defect that greatly controls the electronic properties. Using density functional theory calculations and in situ Raman spectroscopy, how saturation annealing with selenium vapor can stabilize p-type conductivity in cubic AgBiSe 2 alloyed with SnSe at high temperatures is elucidated. With stable and controlled hole concentration, a peak is observed in the weighted mobility and the density-of-states effective mass in AgBiSnSe 3 , implying an increased valley degeneracy in this system. These findings corroborate the importance of considering the defect energetics for exploring the dopability of ternary thermoelectric chalcogenides and engineering electronic bands by controlling self-doping.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnAgH8(OF)4 by Materials Project

MnAgH8(OF)4 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Mn3+ is bonded in an octahedral geometry to two O2- and four F1- atoms. There is one shorter (1.96 Å) and one longer (1.98 Å) Mn–O bond length. There are two shorter (1.99 Å) and two longer (2.08 Å) Mn–F bond lengths. Ag1+ is bonded in a 7-coordinate geometry to five O2- and two equivalent F1- atoms. There are a spread of Ag–O bond distances ranging from 2.41–2.81 Å. Both Ag–F bond lengths are 2.84 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to one O2- and one F1- atom. The H–O bond length is 1.03 Å. The H–F bond length is 1.47 Å. In the second H1+ site, H1+ is bonded in a distorted single-bond geometry to one O2- and one F1- atom. The H–O bond length is 1.01 Å. The H–F bond length is 1.62 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Mn3+, one Ag1+, and two equivalent H1+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mn3+ and two equivalent H1+ atoms. In the third O2- site, O2- is bonded in a water-like geometry to two equivalent Ag1+ and two H1+ atoms. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Mn3+, one Ag1+, and one H1+ atom. In the second F1- site, F1- is bonded in a 2-coordinate geometry to one Mn3+ and one H1+ atom.

36 MATERIALS SCIENCE↗