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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Spontaneous emission dynamics of Eu 3+ ions coupled to hyperbolic metamaterials

We show that sub-wavelength nanostructured systems with tunable electromagnetic properties, such as hyperbolic metamaterials (HMMs), provide a useful platform to tailor spontaneous emission processes. Here, we investigate a system comprising Eu 3+ (NO 3 ) 3 ·6H 2 O nanocrystals on an HMM structure featuring a hexagonal array of Ag nanowires in a porous Al2O 3 matrix. The HMM-coupled Eu 3+ ions exhibit up to a 2.4 fold increase in their decay rate, accompanied by an enhancement of the emission rate of the 5 D 0 → 7 F 2 transition. Using finite-difference time-domain modeling, we corroborate these observations with the increase in the photonic density of states seen by the Eu 3+ ions in the proximity of the HMM. Our results indicate that HMMs can serve as a valuable tool to control the emission from weak transitions and, hence, hint at a route toward more practical applications of rare-earth ions in nanoscale optoelectronics and quantum devices.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Materials Data on Ag5(Sn3S8)2 by Materials Project

Ag5(Sn3S8)2 crystallizes in the orthorhombic C222_1 space group. The structure is three-dimensional. there are four inequivalent Ag+1.60+ sites. In the first Ag+1.60+ site, Ag+1.60+ is bonded to six S2- atoms to form AgS6 octahedra that share corners with two equivalent AgS6 octahedra, corners with four equivalent SnS6 octahedra, edges with three AgS6 octahedra, and edges with five SnS6 octahedra. The corner-sharing octahedra tilt angles range from 1–10°. There are a spread of Ag–S bond distances ranging from 2.60–2.79 Å. In the second Ag+1.60+ site, Ag+1.60+ is bonded to six S2- atoms to form AgS6 octahedra that share corners with six AgS6 octahedra, an edgeedge with one AgS6 octahedra, and edges with six SnS6 octahedra. The corner-sharing octahedra tilt angles range from 8–10°. There are a spread of Ag–S bond distances ranging from 2.73–2.84 Å. In the third Ag+1.60+ site, Ag+1.60+ is bonded to six S2- atoms to form AgS6 octahedra that share corners with two equivalent AgS6 octahedra, corners with four SnS6 octahedra, edges with two AgS6 octahedra, and edges with five SnS6 octahedra. The corner-sharing octahedra tilt angles range from 2–10°. There are a spread of Ag–S bond distances ranging from 2.59–2.77 Å. In the fourth Ag+1.60+ site, Ag+1.60+ is bonded to six S2- atoms to form AgS6 octahedra that share edges with two equivalent AgS6 octahedra and edges with six SnS6 octahedra. There are four shorter (2.64 Å) and two longer (2.70 Å) Ag–S bond lengths. There are four inequivalent Sn4+ sites. In the first Sn4+ site, Sn4+ is bonded to six S2- atoms to form SnS6 octahedra that share edges with four SnS6 octahedra and edges with five AgS6 octahedra. There are a spread of Sn–S bond distances ranging from 2.56–2.65 Å. In the second Sn4+ site, Sn4+ is bonded to six S2- atoms to form SnS6 octahedra that share corners with four AgS6 octahedra, edges with four AgS6 octahedra, and edges with four SnS6 octahedra. The corner-sharing octahedra tilt angles range from 1–8°. There are a spread of Sn–S bond distances ranging from 2.56–2.64 Å. In the third Sn4+ site, Sn4+ is bonded to six S2- atoms to form SnS6 octahedra that share edges with four SnS6 octahedra and edges with six AgS6 octahedra. There are four shorter (2.58 Å) and two longer (2.61 Å) Sn–S bond lengths. In the fourth Sn4+ site, Sn4+ is bonded to six S2- atoms to form SnS6 octahedra that share corners with four equivalent AgS6 octahedra, edges with three AgS6 octahedra, and edges with four SnS6 octahedra. The corner-sharing octahedra tilt angles range from 2–6°. There are four shorter (2.57 Å) and two longer (2.69 Å) Sn–S bond lengths. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a rectangular see-saw-like geometry to two Ag+1.60+ and two Sn4+ atoms. In the second S2- site, S2- is bonded in a rectangular see-saw-like geometry to two Ag+1.60+ and two Sn4+ atoms. In the third S2- site, S2- is bonded in a rectangular see-saw-like geometry to two Ag+1.60+ and two Sn4+ atoms. In the fourth S2- site, S2- is bonded to two Ag+1.60+ and three Sn4+ atoms to form SAg2Sn3 square pyramids that share corners with two equivalent SAg3Sn2 square pyramids and edges with two SAg2Sn3 square pyramids. In the fifth S2- site, S2- is bonded in a rectangular see-saw-like geometry to one Ag+1.60+ and three Sn4+ atoms. In the sixth S2- site, S2- is bonded to three Ag+1.60+ and two Sn4+ atoms to form a mixture of edge and corner-sharing SAg3Sn2 square pyramids. In the seventh S2- site, S2- is bonded in a 3-coordinate geometry to one Ag+1.60+ and two Sn4+ atoms. In the eighth S2- site, S2- is bonded in a rectangular see-saw-like geometry to two Ag+1.60+ and two Sn4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag2BiO3 by Materials Project

Ag2BiO3 crystallizes in the orthorhombic Pnna space group. The structure is three-dimensional. there are two inequivalent Ag+1.50+ sites. In the first Ag+1.50+ site, Ag+1.50+ is bonded in a trigonal planar geometry to three O2- atoms. There are one shorter (2.25 Å) and two longer (2.31 Å) Ag–O bond lengths. In the second Ag+1.50+ site, Ag+1.50+ is bonded in a linear geometry to two equivalent O2- atoms. Both Ag–O bond lengths are 2.14 Å. Bi3+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing BiO6 octahedra. The corner-sharing octahedral tilt angles are 33°. There are a spread of Bi–O bond distances ranging from 2.23–2.30 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to two Ag+1.50+ and two equivalent Bi3+ atoms to form a mixture of edge and corner-sharing OAg2Bi2 tetrahedra. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ag+1.50+ and two equivalent Bi3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgBiSe2 by Materials Project

AgBiSe2 is Caswellsilverite structured and crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are two inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to six Se2- atoms to form AgSe6 octahedra that share corners with six BiSe6 octahedra, edges with six equivalent AgSe6 octahedra, and edges with six BiSe6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are three shorter (2.89 Å) and three longer (2.90 Å) Ag–Se bond lengths. In the second Ag1+ site, Ag1+ is bonded to six equivalent Se2- atoms to form AgSe6 octahedra that share corners with six equivalent BiSe6 octahedra, edges with six equivalent AgSe6 octahedra, and edges with six equivalent BiSe6 octahedra. The corner-sharing octahedral tilt angles are 3°. All Ag–Se bond lengths are 2.89 Å. There are two inequivalent Bi3+ sites. In the first Bi3+ site, Bi3+ is bonded to six Se2- atoms to form BiSe6 octahedra that share corners with six AgSe6 octahedra, edges with six AgSe6 octahedra, and edges with six equivalent BiSe6 octahedra. The corner-sharing octahedral tilt angles are 3°. There are three shorter (2.98 Å) and three longer (2.99 Å) Bi–Se bond lengths. In the second Bi3+ site, Bi3+ is bonded to six equivalent Se2- atoms to form BiSe6 octahedra that share corners with six equivalent AgSe6 octahedra, edges with six equivalent AgSe6 octahedra, and edges with six equivalent BiSe6 octahedra. The corner-sharing octahedral tilt angles are 3°. All Bi–Se bond lengths are 2.98 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Ag1+ and three equivalent Bi3+ atoms to form a mixture of edge and corner-sharing SeAg3Bi3 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second Se2- site, Se2- is bonded to three equivalent Ag1+ and three equivalent Bi3+ atoms to form a mixture of edge and corner-sharing SeAg3Bi3 octahedra. The corner-sharing octahedral tilt angles are 0°. In the third Se2- site, Se2- is bonded to three equivalent Ag1+ and three equivalent Bi3+ atoms to form a mixture of edge and corner-sharing SeAg3Bi3 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
NASA NTRS2019

Uncertainties in the Geostationary Ocean Color Imager (GOCI) Remote Sensing Reflectance for Assessing Diurnal Variability of Biogeochemical Processes

Short-term (sub-diurnal) biological and biogeochemical processes cannot be fully captured by the current suite of polar-orbiting satellite ocean color sensors, as their temporal resolution is limited to potentially one clear image per day. Geostationary sensors, such as the Geostationary Ocean Color Imager (GOCI) from the Republic of Korea, allow the study of these short-term processes because their orbit permit the collection of multiple images throughout each day for any area within the sensor’s field of regard. Assessing the capability to detect sub-diurnal changes in in-water properties caused by physical and biogeochemical processes characteristic of open ocean and coastal ocean ecosystems, however, requires an understanding of the uncertainties introduced by the instrument and/or geophysical retrieval algorithms. This work presents a study of the uncertainties during the daytime period for an ocean region with characteristically low-productivity with the assumption that only small and undetectable changes occur in the in-water properties due to biogeochemical processes during the daytime period. The complete GOCI mission data were processed using NASA’s SeaDAS/l2gen package. The assumption of homogeneity of the study region was tested using three-day sequences and diurnal statistics. This assumption was found to hold based on the minimal diurnal and day-to-day variability in GOCI data products. Relative differences with respect to the midday value were calculated for each hourly observation of the day in order to investigate what time of the day the variability is greater. Also, the influence of the solar zenith angle in the retrieval of remote sensing reflectances and derived products was examined. Finally, we determined that the uncertainties in water-leaving “remote-sensing” reflectance (Rrs) for the 412, 443, 490, 555, 660 and 680 nm bands on GOCI are 8.05 × 10−4, 5.49 × 10−4, 4.48 × 10−4, 2.51 × 10−4, 8.83 × 10−5, and 1.36 × 10−4 sr−1, respectively, and 1.09 × 10−2 mg m−3 for the chlorophyll-a concentration (Chl-a), 2.09 × 10−3 m−1 for the absorption coefficient of chromophoric dissolved organic matter at 412 nm (ag (412)), and 3.7 mg m−3 for particulate organic carbon (POC). These Rrs values can be considered the threshold values for detectable changes of the in-water properties due to biological, physical or biogeochemical processes from GOCI.

Geostationary Ocean Color Imager (GOCI)↗
DOE OSTI2020

Silver Adsorption on Calcium Niobate(001) Nanosheets: Calorimetric Energies That Explain Sinter-Resistant Support

Metal nanoparticles deposited on oxide supports are essential to many technologies, including catalysts, fuel cells and electronics. Therefore, understanding the chemical bonding strength between metal nanoparticles and oxide surfaces is of great interest. The adsorption energetics, adhesion energy and adsorbate structure of Ag on dehydrated HCa 2 Nb 3 O 10 (001) nanosheets at 300 K have been studied using metal adsorption calorimetry and surface spectroscopies. These dehydrated (“dh”) calcium niobate nanosheets “(dh-HCa 2 Nb 3 O 10 (001))” have stoichiometry Ca 4 Nb 6 O 19 . They impart unusual stability to metal nanoparticles when used as catalyst supports and are easy-to-prepare by Langmuir-Blodgett (LB) techniques, highly ordered, and essentially single-crystal surfaces of mixed oxides with a huge ratio of terrace to edge sites. Below monolayer coverage, Ag grows on dh-HCa 2 Nb 3 O 10 (001) as 2D islands of thickness ~2 layers. The differential heat of Ag adsorption is initially ~303 kJ/mol, increasing slowly to ~338 kJ/mol by 0.8 ML. At higher coverages, Ag atoms mainly add on top of these 2D islands, growing 3D nanoparticles of increasing thickness, as the heat decreases asymptotically towards silver’s heat of sublimation (285 kJ/mol). The adhesion energy of Ag(s) to this Ca niobate surface is estimated to be 4.33 J/m 2 , larger than on any oxide surface previously measured. This explains the sinter resistance reported for metal nanoparticles on this support. Electron transfer from Ag into the calcium niobate is also measured. Furthermore, these results demonstrate an easy way to do singlecrystal-type surface science studies - and especially thermochemical measurements - on the complex surfaces of mixed oxides: using LB-deposited perovskite nanosheets and ultrahigh vacuum annealing in O 2 .

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

Materials Data on Li2Ag3F6 by Materials Project

Li2Ag3F6 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded to five F1- atoms to form distorted corner-sharing LiF5 trigonal bipyramids. There are a spread of Li–F bond distances ranging from 1.88–2.01 Å. In the second Li1+ site, Li1+ is bonded to five F1- atoms to form distorted corner-sharing LiF5 trigonal bipyramids. There are a spread of Li–F bond distances ranging from 1.88–2.01 Å. There are three inequivalent Ag+1.33+ sites. In the first Ag+1.33+ site, Ag+1.33+ is bonded in a distorted body-centered cubic geometry to eight F1- atoms. There are a spread of Ag–F bond distances ranging from 2.16–2.70 Å. In the second Ag+1.33+ site, Ag+1.33+ is bonded in a 1-coordinate geometry to nine F1- atoms. There are a spread of Ag–F bond distances ranging from 2.33–2.89 Å. In the third Ag+1.33+ site, Ag+1.33+ is bonded in a 1-coordinate geometry to nine F1- atoms. There are a spread of Ag–F bond distances ranging from 2.33–2.87 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Li1+ and four Ag+1.33+ atoms. In the second F1- site, F1- is bonded in a 6-coordinate geometry to one Li1+ and five Ag+1.33+ atoms. In the third F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Li1+ and four Ag+1.33+ atoms. In the fourth F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Li1+ and four Ag+1.33+ atoms. In the fifth F1- site, F1- is bonded in a 6-coordinate geometry to one Li1+ and five Ag+1.33+ atoms. In the sixth F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Li1+ and four Ag+1.33+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rb2Ag2Sn(PSe3)3 by Materials Project

Rb2Ag2Sn(PSe3)3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded in a 9-coordinate geometry to nine Se2- atoms. There are a spread of Rb–Se bond distances ranging from 3.59–3.82 Å. In the second Rb1+ site, Rb1+ is bonded in a 9-coordinate geometry to nine Se2- atoms. There are a spread of Rb–Se bond distances ranging from 3.51–3.93 Å. There are two inequivalent Ag+1.50+ sites. In the first Ag+1.50+ site, Ag+1.50+ is bonded in a 3-coordinate geometry to three Se2- atoms. There are a spread of Ag–Se bond distances ranging from 2.63–2.69 Å. In the second Ag+1.50+ site, Ag+1.50+ is bonded in a distorted trigonal non-coplanar geometry to three Se2- atoms. There are a spread of Ag–Se bond distances ranging from 2.65–2.72 Å. Sn4+ is bonded in a distorted T-shaped geometry to three Se2- atoms. There are a spread of Sn–Se bond distances ranging from 2.75–2.84 Å. There are three inequivalent P3+ sites. In the first P3+ site, P3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are a spread of P–Se bond distances ranging from 2.15–2.26 Å. In the second P3+ site, P3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are one shorter (2.19 Å) and two longer (2.25 Å) P–Se bond lengths. In the third P3+ site, P3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are a spread of P–Se bond distances ranging from 2.19–2.26 Å. There are nine inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 1-coordinate geometry to three Rb1+ and one P3+ atom. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to two Rb1+, one Sn4+, and one P3+ atom. In the third Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent Rb1+, one Sn4+, and one P3+ atom. In the fourth Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent Rb1+, one Ag+1.50+, and one P3+ atom. In the fifth Se2- site, Se2- is bonded in a 2-coordinate geometry to two equivalent Rb1+, one Ag+1.50+, and one P3+ atom. In the sixth Se2- site, Se2- is bonded to two equivalent Rb1+, one Ag+1.50+, and one P3+ atom to form distorted edge-sharing SeRb2AgP trigonal pyramids. In the seventh Se2- site, Se2- is bonded in a 3-coordinate geometry to one Rb1+, two equivalent Ag+1.50+, and one P3+ atom. In the eighth Se2- site, Se2- is bonded in a 4-coordinate geometry to two Rb1+, one Sn4+, and one P3+ atom. In the ninth Se2- site, Se2- is bonded in a 2-coordinate geometry to two Rb1+, one Ag+1.50+, and one P3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li6Ag3F10 by Materials Project

Li6Ag3F10 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are six inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a rectangular see-saw-like geometry to four F1- atoms. There are a spread of Li–F bond distances ranging from 1.87–1.97 Å. In the second Li1+ site, Li1+ is bonded to four F1- atoms to form LiF4 tetrahedra that share corners with three LiF4 tetrahedra and a cornercorner with one AgF5 trigonal bipyramid. There are a spread of Li–F bond distances ranging from 1.86–1.93 Å. In the third Li1+ site, Li1+ is bonded to four F1- atoms to form LiF4 tetrahedra that share corners with four LiF4 tetrahedra and a cornercorner with one AgF5 trigonal bipyramid. There are a spread of Li–F bond distances ranging from 1.91–1.93 Å. In the fourth Li1+ site, Li1+ is bonded to four F1- atoms to form LiF4 tetrahedra that share corners with five LiF4 tetrahedra and corners with two equivalent AgF5 trigonal bipyramids. There are a spread of Li–F bond distances ranging from 1.84–1.93 Å. In the fifth Li1+ site, Li1+ is bonded to four F1- atoms to form distorted LiF4 tetrahedra that share corners with four LiF4 tetrahedra, corners with three equivalent AgF5 trigonal bipyramids, and an edgeedge with one LiF4 tetrahedra. There are a spread of Li–F bond distances ranging from 1.87–2.07 Å. In the sixth Li1+ site, Li1+ is bonded to four F1- atoms to form distorted LiF4 tetrahedra that share corners with four LiF4 tetrahedra, corners with three equivalent AgF5 trigonal bipyramids, and an edgeedge with one LiF4 tetrahedra. There are a spread of Li–F bond distances ranging from 1.85–2.00 Å. There are three inequivalent Ag+1.33+ sites. In the first Ag+1.33+ site, Ag+1.33+ is bonded in a 4-coordinate geometry to four F1- atoms. There are a spread of Ag–F bond distances ranging from 2.22–2.73 Å. In the second Ag+1.33+ site, Ag+1.33+ is bonded in a 6-coordinate geometry to six F1- atoms. There are a spread of Ag–F bond distances ranging from 2.32–2.84 Å. In the third Ag+1.33+ site, Ag+1.33+ is bonded to five F1- atoms to form distorted AgF5 trigonal bipyramids that share corners with ten LiF4 tetrahedra. There are a spread of Ag–F bond distances ranging from 2.20–2.44 Å. There are ten inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to three Li1+ and two equivalent Ag+1.33+ atoms. In the second F1- site, F1- is bonded in a 4-coordinate geometry to two Li1+ and two equivalent Ag+1.33+ atoms. In the third F1- site, F1- is bonded in a distorted see-saw-like geometry to three Li1+ and one Ag+1.33+ atom. In the fourth F1- site, F1- is bonded in a 4-coordinate geometry to three Li1+ and one Ag+1.33+ atom. In the fifth F1- site, F1- is bonded in a distorted T-shaped geometry to one Li1+ and two Ag+1.33+ atoms. In the sixth F1- site, F1- is bonded in a distorted see-saw-like geometry to three Li1+ and one Ag+1.33+ atom. In the seventh F1- site, F1- is bonded in a 3-coordinate geometry to two Li1+ and two Ag+1.33+ atoms. In the eighth F1- site, F1- is bonded in a distorted trigonal pyramidal geometry to two Li1+ and two Ag+1.33+ atoms. In the ninth F1- site, F1- is bonded in a distorted rectangular see-saw-like geometry to three Li1+ and one Ag+1.33+ atom. In the tenth F1- site, F1- is bonded in a 3-coordinate geometry to two Li1+ and one Ag+1.33+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Composition-Dependent Photoluminescence Properties and Anti-Counterfeiting Applications of A 2 AgX 3 (A = Rb, Cs; X = Cl, Br, I)

Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue-emitting all-inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. In this work, the preparation of silver(I) halides A 2 AgX 3 (A = Rb, Cs; X = Cl, Br, I) through solid-state synthesis is reported. In contrast to the Cu(I) analogs, A 2 AgX 3 are broad-band emitters sensitive to A and X site substitutions. First-principle calculations show that defect-bound excitons are responsible for the observed main PL peaks in Rb 2 AgX 3 and that self-trapped excitons (STEs) contribute to a minor PL peak in Rb 2 AgBr 3 . This is in sharp contrast to Rb 2 CuX 3 , in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A 2 AgX 3 significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A 2 AgX 3 are prepared and successfully used in anti-counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A 2 AgX 3 suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Hybrid Layered Double Perovskite Halides of Transition Metals

Hybrid layered double perovskite (HLDP) halides comprise hexacoordinated 1+ and 3+ metals in the octahedral sites within a perovskite layer and organic amine cations between the layers. Here, progress on such materials has hitherto been limited to compounds containing main group 3+ ions isoelectronic with Pb II (such as Sb III and Bi III ). Furthermore, we report eight HLDP halides from the A 2 M I M III X 8 family, where A = para-phenylenediammonium (PPDA), 1,4-butanediammonium (1,4-BDA), or 1,3-propanediammonium (1,3-PDA); M I = Cu or Ag; M III = Ru or Mo; X = Cl or Br. The optical band gaps, which lie in the range 1.55 to 2.05 eV, are tunable according to the layer composition, but are largely independent of the spacer. Magnetic measurements carried out for (PPDA) 2 Ag I Ru III Cl 8 and (PPDA) 2 Ag I Mo III Cl 8 show no obvious evidence of a magnetic ordering transition. While the t 2g 3 Mo III compound displays Curie–Weiss behavior for a spin-only d 3 ion, the t 2g 5 Ru III compound displays marked deviations from the Kotani theory.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Meteoritic and non-meteoritic trace elements in Luna 16 samples.

Two Luna 16 soils have been analyzed for Ag, Au, Bi, Br, Cd, Co, Cs, Cu, Ga, Ge, In, Ur, Ni, Rb, Re, Sb, Se, Te, Tl, and Zn. A meteoritic component similar to that in Apollo 11 and 12 soils seems to be present, corresponding to about 1.5 to 2% Cl chondrites or equivalent. It probably consists largely of micrometeorites. Three elements show strong enrichments compared to Apollo 11 and 12 soils: Cd (5 x to 200 x), Ag (5 x to 10 x), and Bi (3 x). Presumably these elements were brought in by Cd-Ag-Bi rich material, similar to that in Unit VI of Apollo core 12028.

Laul, J. C.↗
NASA NTRS1976

Widths of atomic 4s and 4p vacancy states, Z between 46 and 50

X-ray photoelectron and Auger spectra involving N sub 1, N sub 2, and N sub 3 vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free-atom calculations. As previously observed in Cu and Zn Auger spectra that involve 3d-band electrons, free-atom characteristics are found, with regard to widths and structure, in the Ag and Cd M sub 4-N sub 4,5 N sub 4,5 and M sub 5-N sub 4,5 N sub 4,5 Auger spectra that arise from transitions of 4d-band electrons. Theoretical N sub 1 widths computed with calculated free-atom Auger energies agree well with measurements. Theory, however, predicts wider N sub 2 than N sub 3 vacancy states (as observed for Xe), while the measured N sub 2 and N sub 3 widths are nearly equal to each other and to the average of the calculated N sub 2 and N sub 3 widths. The calculations are made difficult by the exceedingly short lifetime of some 4 p vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation to the transition energy and to the fine details of the atomic potential.

Chen, M. H.↗
DOE OSTI2020

Materials Data on LiAg2F4 by Materials Project

LiAg2F4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Li1+ is bonded to four F1- atoms to form LiF4 tetrahedra that share corners with four equivalent AgF6 pentagonal pyramids and an edgeedge with one AgF6 pentagonal pyramid. There are a spread of Li–F bond distances ranging from 1.86–1.93 Å. There are two inequivalent Ag+1.50+ sites. In the first Ag+1.50+ site, Ag+1.50+ is bonded to six F1- atoms to form distorted AgF6 pentagonal pyramids that share corners with four equivalent LiF4 tetrahedra, edges with two equivalent AgF6 pentagonal pyramids, and an edgeedge with one LiF4 tetrahedra. There are a spread of Ag–F bond distances ranging from 2.21–2.65 Å. In the second Ag+1.50+ site, Ag+1.50+ is bonded in a distorted rectangular see-saw-like geometry to four F1- atoms. There are a spread of Ag–F bond distances ranging from 2.17–2.28 Å. There are four inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to one Li1+ and two Ag+1.50+ atoms. In the second F1- site, F1- is bonded in a 4-coordinate geometry to one Li1+ and three Ag+1.50+ atoms. In the third F1- site, F1- is bonded in a 3-coordinate geometry to one Li1+ and two Ag+1.50+ atoms. In the fourth F1- site, F1- is bonded in a 1-coordinate geometry to one Li1+ and three Ag+1.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effects of the method of active site characterization for determining structure-sensitivity in Ag-catalyzed ethylene epoxidation

We report catalysts have been prepared on a low surface area α-Al 2 O 3 support used commercially for previous generation olefin epoxidation catalysts. Prescreening of the low surface area alumina (0.73 m 2 /g) indicated the absence of acid catalyzed isomerization of EO at an evaluation temperature of 210 °C. A 0.1 wt% Ag base material synthesized by incipient wetness impregnation of AgNO 3 was used as a base material for electroless deposition (ED) of additional Ag to increase particle sizes by controlled reduction of Ag + directly onto the preexisting Ag surface to form weight loadings between 0.3 and 5.0 wt% metal. A 12 wt% Ag/α-Al 2 O 3 using Ag 2 C 2 O 4 as the Ag precursor was also prepared to compare performance of the ED samples with a catalyst more typical of industrial formulations. Characterization by SEM, STEM, and hydrogen titration of oxygen precovered Ag characterized before and after catalytic evaluation indicated that microscopy is required to accurately represent distributions of Ag particle sizes, but H 2 titration of O-precovered Ag gives the best representation of active sites since it directly counts the number of Ag surface sites. Larger particles >100 nm are resistant to both Ag sintering and carbon foulant; TOF values were relatively insensitive to particle size with only a 2.2 × difference between the best and worst performing samples. Selectivity, which is not a function of TOF, shows the most significant structure sensitivity effect where particle sizes follow the trend 67 nm ≈ 92 nm (58% EO) < 157 nm (67% EO) < 211–542 nm (73% EO). The lower EO selectivities were also correlated with increased fouling for the smaller Ag sizes, suggesting that more strongly bound EO precursor(s) leads to combustion and CO 2 /H 2 O formation.

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

Materials Data on U2Ag(GeO6)2 by Materials Project

U2Ag(GeO6)2 crystallizes in the orthorhombic Ama2 space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded to seven O atoms to form distorted UO7 pentagonal bipyramids that share corners with three equivalent GeO4 tetrahedra, edges with two equivalent UO7 pentagonal bipyramids, and an edgeedge with one GeO4 tetrahedra. There are a spread of U–O bond distances ranging from 1.82–2.48 Å. In the second U site, U is bonded to seven O atoms to form distorted UO7 pentagonal bipyramids that share corners with three equivalent GeO4 tetrahedra, edges with two equivalent UO7 pentagonal bipyramids, and an edgeedge with one GeO4 tetrahedra. There are a spread of U–O bond distances ranging from 1.81–2.50 Å. Ag is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Ag–O bond distances ranging from 2.15–2.62 Å. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded to four O atoms to form GeO4 tetrahedra that share corners with three equivalent UO7 pentagonal bipyramids, a cornercorner with one GeO4 tetrahedra, and an edgeedge with one UO7 pentagonal bipyramid. There are a spread of Ge–O bond distances ranging from 1.75–1.78 Å. In the second Ge site, Ge is bonded to four O atoms to form GeO4 tetrahedra that share corners with three equivalent UO7 pentagonal bipyramids, a cornercorner with one GeO4 tetrahedra, and an edgeedge with one UO7 pentagonal bipyramid. There are a spread of Ge–O bond distances ranging from 1.74–1.78 Å. There are ten inequivalent O sites. In the first O site, O is bonded in a distorted bent 150 degrees geometry to one U and one Ge atom. In the second O site, O is bonded in a distorted single-bond geometry to one U and two equivalent Ag atoms. In the third O site, O is bonded in a single-bond geometry to one U atom. In the fourth O site, O is bonded in a distorted bent 120 degrees geometry to one U and one Ge atom. In the fifth O site, O is bonded in a bent 120 degrees geometry to two Ge atoms. In the sixth O site, O is bonded in a water-like geometry to two equivalent Ag atoms. In the seventh O site, O is bonded in a 3-coordinate geometry to one U and two equivalent Ag atoms. In the eighth O site, O is bonded in a single-bond geometry to one U atom. In the ninth O site, O is bonded in a 3-coordinate geometry to two U and one Ge atom. In the tenth O site, O is bonded in a 3-coordinate geometry to two U and one Ge atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Small bimetallic clusters Agn-1M (M = Au, Co, Cu, Ni, Pd, Pt; n = 3, 9, 15): Density functional theory and genetic algorithm

We investigated the effect of size and composition on the properties of bimetallic nanoclusters. The geometric structures, stabilities, and electronic properties of size-selected Ag n-1 M (M = Au, Co, Cu, Ni, Pd, Pt; n = 3, 9, 15) bimetallic nanoclusters are systematically analyzed using spin-polarized density functional theory (DFT) within the generalized gradient approximation (GGA). We determine the most stable geometries for these clusters using a genetic algorithm (GA) in combination with DFT. Our results show that doping pure silver clusters with an M atom (transition metal), referred to as a “guest atom”, increases the stability as compared to pure Ag n (n = 3, 9, 15) clusters. The results for various properties including formation energy per atom, electronic structure, magnetic moments, and vibrational density of states (VDOS) are evaluated as a function of both size and composition of the system. The adsorption of selected bimetallic clusters on hydroxylated alumina substrate shows weak binding and minor changes in geometric properties except for Ag 8 Pt.

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

Materials Data on Sc6AgTe2 by Materials Project

Sc6AgTe2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are six inequivalent Sc sites. In the first Sc site, Sc is bonded in a 1-coordinate geometry to one Ag and one Te atom. The Sc–Ag bond length is 3.21 Å. The Sc–Te bond length is 2.98 Å. In the second Sc site, Sc is bonded in a 4-coordinate geometry to four Te atoms. There are two shorter (2.96 Å) and two longer (2.98 Å) Sc–Te bond lengths. In the third Sc site, Sc is bonded to three equivalent Ag and two equivalent Te atoms to form distorted ScAg3Te2 trigonal bipyramids that share corners with two equivalent ScAg2Te3 square pyramids, edges with three equivalent ScAg2Te3 square pyramids, and edges with four equivalent ScAg3Te2 trigonal bipyramids. There are two shorter (2.90 Å) and one longer (3.02 Å) Sc–Ag bond lengths. Both Sc–Te bond lengths are 3.00 Å. In the fourth Sc site, Sc is bonded in a 3-coordinate geometry to two equivalent Ag and one Te atom. Both Sc–Ag bond lengths are 2.86 Å. The Sc–Te bond length is 3.00 Å. In the fifth Sc site, Sc is bonded to two equivalent Ag and three Te atoms to form distorted ScAg2Te3 square pyramids that share corners with two equivalent ScAg3Te2 trigonal bipyramids, edges with two equivalent ScAg2Te3 square pyramids, and edges with three equivalent ScAg3Te2 trigonal bipyramids. Both Sc–Ag bond lengths are 2.85 Å. There are one shorter (2.93 Å) and two longer (2.97 Å) Sc–Te bond lengths. In the sixth Sc site, Sc is bonded in a 4-coordinate geometry to one Ag and four Te atoms. The Sc–Ag bond length is 3.37 Å. There are a spread of Sc–Te bond distances ranging from 2.94–3.15 Å. Ag is bonded in a 9-coordinate geometry to nine Sc atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 8-coordinate geometry to eight Sc atoms. In the second Te site, Te is bonded to seven Sc atoms to form distorted edge-sharing TeSc7 pentagonal bipyramids.

36 MATERIALS SCIENCE↗