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All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Fine resolution chronology based on initial Sr-87/Sr-86

It has been recognized that small variations in initial Sr-87/Sr-86 (Sr(sub I)), can provide a fine scale relative chronology for the chemical fractionation of materials with low Rb/Sr from parent reservoirs with high Rb/Sr. Similarly, Sr(sub I), as determined for low Rb/Sr phases in meteorites, may permit a fine resolution chronology of the recrystallization or metamorphism of planetary materials. For the establishment of a primitive Sr-87/Sr-86 chronology, it is important to search for samples with extremely low Rb/Sr for which the measured Sr-87/Sr-86 is below BABI, in which case the primitive nature of the Sr can be directly established. Using the measured Rb/Sr to calculate an initial Sr-87/Sr-86 can introduce substantial uncertainty if the Rb-Sr are disturbed. We report Sr-87/Sr-86 in plagioclase from silicate pebbles from the Vaca Muerta mesosiderite on which we have reported Sm-147-Nd-143 and Ne-142 correlations. For the purpose of cross-calibration with our previous work we have performed extensive new measurements on Angra dos Reis and on anorthite from Moore County, which have very low Rb/Sr and primitive Sr-87/Sr-86.

Stewart, B. W.↗
DOE OSTI2020

Materials Data on Sr(H2O3)2 by Materials Project

Sr(H2O3)2 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Sr is bonded in a 10-coordinate geometry to ten O atoms. There are a spread of Sr–O bond distances ranging from 2.61–2.81 Å. There are four inequivalent H sites. In the first H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.07 Å) and one longer (1.44 Å) H–O bond length. In the second H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.07 Å) and one longer (1.44 Å) H–O bond length. In the third H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.04 Å) and one longer (1.53 Å) H–O bond length. In the fourth H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.04 Å) and one longer (1.53 Å) H–O bond length. There are six inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the second O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the third O site, O is bonded in a single-bond geometry to one Sr and one H atom. In the fourth O site, O is bonded in a single-bond geometry to one Sr and one H atom. In the fifth O site, O is bonded in a 2-coordinate geometry to two equivalent Sr and two H atoms. In the sixth O site, O is bonded in a 2-coordinate geometry to two equivalent Sr and two H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(H2O3)2 by Materials Project

Sr(H2O3)2 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Sr is bonded in a 10-coordinate geometry to ten O atoms. There are a spread of Sr–O bond distances ranging from 2.59–2.81 Å. There are four inequivalent H sites. In the first H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.04 Å) and one longer (1.52 Å) H–O bond length. In the second H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.06 Å) and one longer (1.47 Å) H–O bond length. In the third H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.10 Å) and one longer (1.38 Å) H–O bond length. In the fourth H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.14 Å) and one longer (1.31 Å) H–O bond length. There are six inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the second O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the third O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the fourth O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the fifth O site, O is bonded in a distorted bent 120 degrees geometry to one Sr and two H atoms. In the sixth O site, O is bonded in a 2-coordinate geometry to one Sr and two H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(H2O3)2 by Materials Project

Sr(H2O3)2 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Sr is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of Sr–O bond distances ranging from 2.57–2.89 Å. There are four inequivalent H sites. In the first H site, H is bonded in a bent 150 degrees geometry to two O atoms. There is one shorter (1.07 Å) and one longer (1.46 Å) H–O bond length. In the second H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.05 Å) and one longer (1.52 Å) H–O bond length. In the third H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.03 Å) and one longer (1.55 Å) H–O bond length. In the fourth H site, H is bonded in a distorted bent 150 degrees geometry to two O atoms. There is one shorter (1.06 Å) and one longer (1.50 Å) H–O bond length. There are six inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the second O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the third O site, O is bonded in a single-bond geometry to two equivalent Sr and one H atom. In the fourth O site, O is bonded in a single-bond geometry to one Sr and one H atom. In the fifth O site, O is bonded in a 2-coordinate geometry to one Sr and two H atoms. In the sixth O site, O is bonded in a distorted bent 120 degrees geometry to one Sr and two H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(AsO4)2 by Materials Project

Sr(AsO4)2 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Sr is bonded in a 6-coordinate geometry to eight O atoms. There are a spread of Sr–O bond distances ranging from 2.41–3.21 Å. There are two inequivalent As sites. In the first As site, As is bonded in a rectangular see-saw-like geometry to four O atoms. There are a spread of As–O bond distances ranging from 1.64–1.88 Å. In the second As site, As is bonded in a tetrahedral geometry to four O atoms. There are a spread of As–O bond distances ranging from 1.66–1.87 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a distorted trigonal planar geometry to two equivalent Sr and one As atom. In the second O site, O is bonded in a distorted single-bond geometry to one Sr, one As, and one O atom. The O–O bond length is 1.48 Å. In the third O site, O is bonded in a single-bond geometry to one As atom. In the fourth O site, O is bonded in a 1-coordinate geometry to one Sr, one As, and one O atom. In the fifth O site, O is bonded in a 1-coordinate geometry to one Sr, one As, and one O atom. The O–O bond length is 1.49 Å. In the sixth O site, O is bonded in a distorted trigonal planar geometry to two equivalent Sr and one As atom. In the seventh O site, O is bonded in a distorted bent 150 degrees geometry to one Sr and one As atom. In the eighth O site, O is bonded in a distorted single-bond geometry to one As atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(H2O3)2 by Materials Project

Sr(H2O3)2 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. Sr is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of Sr–O bond distances ranging from 2.57–2.87 Å. There are four inequivalent H sites. In the first H site, H is bonded in a single-bond geometry to two O atoms. There is one shorter (1.00 Å) and one longer (1.74 Å) H–O bond length. In the second H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the third H site, H is bonded in a single-bond geometry to two O atoms. There is one shorter (0.99 Å) and one longer (1.73 Å) H–O bond length. In the fourth H site, H is bonded in a distorted single-bond geometry to two O atoms. There is one shorter (1.01 Å) and one longer (1.67 Å) H–O bond length. There are six inequivalent O sites. In the first O site, O is bonded in a water-like geometry to two equivalent Sr and two H atoms. In the second O site, O is bonded in a 3-coordinate geometry to one Sr, one H, and one O atom. The O–O bond length is 1.36 Å. In the third O site, O is bonded in a water-like geometry to two equivalent Sr and two H atoms. In the fourth O site, O is bonded in a 3-coordinate geometry to two equivalent Sr and one O atom. In the fifth O site, O is bonded in a 3-coordinate geometry to one Sr, one H, and one O atom. The O–O bond length is 1.35 Å. In the sixth O site, O is bonded in a distorted trigonal planar geometry to one Sr, one H, and one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cubic Crystal Structure Formation and Optical Properties within the Ag–B II –M IV –X (B II = Sr, Pb; M IV = Si, Ge, Sn; X = S, Se) Family of Semiconductors

Quaternary chalcogenide semiconductors are promising materials for energy conversion and nonlinear optical applications, with properties tunable primarily by varying the elemental composition and crystal structure. Here, we first analyze the connections among several cubic crystal structure types, as well as the orthorhombic Ag 2 PbGeS 4 -type structure, reported for select members within the Ag–B II –M IV –X (B II = Sr, Pb; M IV = Si, Ge, Sn; X = S, Se) compositional space. Focusing on the Ag–Pb–Si–S and Ag–Sr–Sn–S systems, we show that one structure type, with the formulas Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , is favored. We have prepared powder and single-crystal samples of Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , showing that each takes on the noncentrosymmetric cubic space group I$\bar{43}$d and is isostructural to the previously reported compound Ag 2 Sr 3 Ge 2 Se 8 . Through hybrid density functional theory calculations, these cubic compounds are demonstrated to be (quasi-)direct band gap semiconductors with high densities of states at the band maxima. Furthermore, the band-gap energies are measured by reflectance spectroscopy as 1.95(3) and 2.66(4) eV for Ag 2 Pb 3 Si 2 S 8 and Ag 2 Sr 3 Sn 2 S 8 , respectively. We further measure the optical properties and show the electronic band structures of three other isostructural A I –B II –M IV –X-type materials, i.e., Ag 2 Sr 3 Si 2 S 8 , Ag 2 Sr 3 Ge 2 S 8 , and Ag 2 Sr 3 Ge 2 Se 8 , showing that the band gaps can be predictably tuned by element substitution. Detailed visual analyses of the different structures and of their relationships with other members of the Ag–B II –M IV –X compositional family provide a basis for a broader understanding of the structure formation and optoelectronic properties within the quaternary chalcogenide semiconductor family.

14 SOLAR ENERGY↗
DOE OSTI2020

Subaru Near-infrared Imaging Polarimetry of Misaligned Disks around the SR 24 Hierarchical Triple System

The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.″1 resolution near-infrared polarized intensity images of the circumstellar structures around SR 24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the near-IR (NIR) polarization disk around SR 24S are 55° and 137 au, respectively, those around SR 24N are 110° and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR 24S shows strong asymmetry, whereas the circumsecondary disk around SR 24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in {sup 12}CO observations in terms of its size and elongation direction. This consistency is because both NIR and {sup 12}CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR 24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR 24N as a circumbinary disk surrounding the SR 24Nb–Nc system.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2019

Subaru Near-Infrared Imaging Polarimetry of Misaligned Disks Around the SR 24 Hierachical Triple System

The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 0.″1 resolution near-infrared polarized intensity images of the circumstellar structures around SR 24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the near-IR (NIR) polarization disk around SR 24S are 55° and 137 au, respectively, those around SR 24N are 110° and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR 24S shows strong asymmetry, whereas the circumsecondary disk around SR 24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in 12CO observations in terms of its size and elongation direction. This consistency is because both NIR and 12CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR 24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR 24N as a circumbinary disk surrounding the SR 24Nb─Nc system.

Satoshi Mayama↗
DOE OSTI2020

The Influence of Alkalinity on the Uptake of Cs{sup +} and Sr{sup 2+} by Cation-substituted Natisites in Sodium-bearing Conditions - 20336

The titanosilicate natisite (Na{sub 2}TiSiO{sub 5}) is a kinetic phase of the mineral sitinakite (Na{sub 2}Ti{sub 2}O{sub 3}SiO{sub 4}.2H{sub 2}O), which is a reference material in the removal of Cs and Sr from radioactive high-level waste. Natisite is disregarded in the literature as a candidate sorbent for Cs and Sr, despite being more thermally stable than sitinakite, which is a critical property for this application. Replacing portion of the Ti in natisite by other metals is believed to enhance natisite sorption properties. In nuclear waste remediation, Cs and Sr are contained in high-salinity liquid wastes that can either be highly acidic or alkaline. In the present study, Al-, Sn-, and Zr-natisites were synthesized, and compared to pure natisite and sitinakite in batch experiments. Five concentrations of NaOH and NaNO{sub 3} (i.e. source of Na{sup +}) mimicking conditions of high alkalinity, and competing Na{sup +} ions, respectively, were evaluated. Sorption results demonstrate that sitinakite is generally more effective than all four natisites in removing Cs and Sr. However, sitinakite uptake mechanism seems to deteriorate at increasing concentrations of base and Na{sup +}. Although less selective than sitinakite, all natisite sorbents provided a less dramatic decline in Cs and Sr uptake through increasing molarities. Overall, there was an improvement in the sorption of Cs and Sr by the metal-substituted materials over natisite and, in neither of the testing solutions, natisite outperformed its substituted variants. In highly alkaline solutions, Sn- and Zr-Natisite provided for exceptional removal for Sr, removing more than twice the amount sorbed by sitinakite at 0.1 M NaOH. The results obtained for Sr uptake by all four natisite materials in alkaline solutions are promising, especially considering the highly alkaline nature of wastes from the nuclear industry. Future studies should investigate the sorption mechanisms responsible for natisite selectivity for Sr at high pH. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Materials Data on Sr(GaAu)2 by Materials Project

Sr(AuGa)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Sr is bonded in a 12-coordinate geometry to eight Au and eight Ga atoms. There are four shorter (3.47 Å) and four longer (3.51 Å) Sr–Au bond lengths. There are four shorter (3.48 Å) and four longer (3.52 Å) Sr–Ga bond lengths. There are two inequivalent Au sites. In the first Au site, Au is bonded in a 9-coordinate geometry to four equivalent Sr and five Ga atoms. There are one shorter (2.61 Å) and four longer (2.67 Å) Au–Ga bond lengths. In the second Au site, Au is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Ga atoms. All Au–Ga bond lengths are 2.65 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a 5-coordinate geometry to four equivalent Sr and five Au atoms. In the second Ga site, Ga is bonded to four equivalent Sr and four equivalent Au atoms to form a mixture of distorted edge and face-sharing GaSr4Au4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(InAu)2 by Materials Project

Sr(AuIn)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Sr is bonded in a 12-coordinate geometry to seven Au and four In atoms. There are a spread of Sr–Au bond distances ranging from 3.25–3.58 Å. There are a spread of Sr–In bond distances ranging from 3.59–3.63 Å. There are two inequivalent Au sites. In the first Au site, Au is bonded in a 9-coordinate geometry to four equivalent Sr and five In atoms. There are a spread of Au–In bond distances ranging from 2.78–2.95 Å. In the second Au site, Au is bonded in a 9-coordinate geometry to three equivalent Sr, two equivalent Au, and four In atoms. Both Au–Au bond lengths are 2.90 Å. There are a spread of Au–In bond distances ranging from 2.76–2.89 Å. There are two inequivalent In sites. In the first In site, In is bonded to two equivalent Sr and four Au atoms to form a mixture of distorted corner and edge-sharing InSr2Au4 tetrahedra. In the second In site, In is bonded in a 5-coordinate geometry to two equivalent Sr and five Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(H8O5)2 by Materials Project

Sr(H8O5)2 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two Sr(H8O5)2 sheets oriented in the (0, 0, 1) direction. Sr is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Sr–O bond distances ranging from 2.61–2.67 Å. There are eight inequivalent H sites. In the first H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the second H site, H is bonded in a single-bond geometry to two O atoms. There is one shorter (1.02 Å) and one longer (1.68 Å) H–O bond length. In the third H site, H is bonded in a single-bond geometry to two O atoms. There is one shorter (1.01 Å) and one longer (1.69 Å) H–O bond length. In the fourth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 1.00 Å. In the fifth H site, H is bonded in a single-bond geometry to two O atoms. There is one shorter (1.01 Å) and one longer (1.70 Å) H–O bond length. In the sixth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.99 Å. In the seventh H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the eighth H site, H is bonded in a distorted single-bond geometry to two O atoms. There is one shorter (1.03 Å) and one longer (1.66 Å) H–O bond length. There are five inequivalent O sites. In the first O site, O is bonded in a 5-coordinate geometry to four H and one O atom. The O–O bond length is 1.51 Å. In the second O site, O is bonded in a water-like geometry to one Sr and two H atoms. In the third O site, O is bonded in a water-like geometry to one Sr and two H atoms. In the fourth O site, O is bonded in a water-like geometry to one Sr and two H atoms. In the fifth O site, O is bonded in a distorted bent 120 degrees geometry to one Sr and two H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(H8O5)2 by Materials Project

Sr(H8O5)2 crystallizes in the monoclinic C2 space group. The structure is two-dimensional and consists of one Sr(H8O5)2 sheet oriented in the (0, 0, 1) direction. Sr is bonded in a distorted body-centered cubic geometry to eight O atoms. There are a spread of Sr–O bond distances ranging from 2.59–2.65 Å. There are eight inequivalent H sites. In the first H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.02 Å) and one longer (1.62 Å) H–O bond length. In the second H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the third H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.02 Å) and one longer (1.60 Å) H–O bond length. In the fourth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the fifth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the sixth H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.02 Å) and one longer (1.63 Å) H–O bond length. In the seventh H site, H is bonded in a distorted single-bond geometry to two O atoms. There is one shorter (1.01 Å) and one longer (1.68 Å) H–O bond length. In the eighth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. There are five inequivalent O sites. In the first O site, O is bonded in a 5-coordinate geometry to four H and one O atom. The O–O bond length is 1.49 Å. In the second O site, O is bonded in a water-like geometry to one Sr and two H atoms. In the third O site, O is bonded in a water-like geometry to one Sr and two H atoms. In the fourth O site, O is bonded in a water-like geometry to one Sr and two H atoms. In the fifth O site, O is bonded in a distorted water-like geometry to one Sr and two H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(SnAu)2 by Materials Project

Sr(AuSn)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Sr is bonded in a 12-coordinate geometry to eight Au and eight Sn atoms. There are four shorter (3.63 Å) and four longer (3.66 Å) Sr–Au bond lengths. There are four shorter (3.62 Å) and four longer (3.80 Å) Sr–Sn bond lengths. There are two inequivalent Au sites. In the first Au site, Au is bonded in a 4-coordinate geometry to four equivalent Sr and four equivalent Sn atoms. All Au–Sn bond lengths are 2.80 Å. In the second Au site, Au is bonded in a 9-coordinate geometry to four equivalent Sr and five Sn atoms. There are one shorter (2.67 Å) and four longer (2.85 Å) Au–Sn bond lengths. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded to four equivalent Sr and four equivalent Au atoms to form a mixture of distorted face and edge-sharing SnSr4Au4 tetrahedra. In the second Sn site, Sn is bonded in a 9-coordinate geometry to four equivalent Sr and five Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(NO5)2 by Materials Project

Sr(NO4)2O2 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of four hydrogen peroxide molecules and two Sr(NO4)2 sheets oriented in the (0, 1, 0) direction. In each Sr(NO4)2 sheet, Sr is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Sr–O bond distances ranging from 2.57–3.13 Å. N is bonded in a trigonal planar geometry to three O atoms. There are a spread of N–O bond distances ranging from 1.22–1.32 Å. There are four inequivalent O sites. In the first O site, O is bonded in a distorted water-like geometry to one Sr and one N atom. In the second O site, O is bonded in a 1-coordinate geometry to two equivalent Sr and one N atom. In the third O site, O is bonded in a single-bond geometry to one N atom. In the fourth O site, O is bonded in a bent 120 degrees geometry to one Sr and one O atom. The O–O bond length is 1.23 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(SnHg)2 by Materials Project

Sr(HgSn)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Sr is bonded in a 12-coordinate geometry to seven Hg and seven Sn atoms. There are a spread of Sr–Hg bond distances ranging from 3.50–3.92 Å. There are a spread of Sr–Sn bond distances ranging from 3.58–3.79 Å. There are two inequivalent Hg sites. In the first Hg site, Hg is bonded in a 8-coordinate geometry to four equivalent Sr and four Sn atoms. There are a spread of Hg–Sn bond distances ranging from 2.92–3.21 Å. In the second Hg site, Hg is bonded in a 7-coordinate geometry to three equivalent Sr and four Sn atoms. There are a spread of Hg–Sn bond distances ranging from 2.91–3.26 Å. There are two inequivalent Sn sites. In the first Sn site, Sn is bonded in a 8-coordinate geometry to three equivalent Sr, four Hg, and one Sn atom. The Sn–Sn bond length is 2.92 Å. In the second Sn site, Sn is bonded in a 9-coordinate geometry to four equivalent Sr, four Hg, and one Sn atom. The Sn–Sn bond length is 2.95 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanism for Acetone and Crotonaldehyde Production during Steam Reforming of Ethanol over La 0.7 Sr 0.3 MnO 3–x Perovskite: Evidence for a Shared C4 Aldol Addition Intermediate

Here a mechanistic study was conducted on the catalytic conversion of ethanol over La 0.7 Sr 0.3 MnO 3–x perovskite catalysts in the presence and absence of water. The study sought insights into the path of C–C coupling toward acetone and crotonaldehyde and also into clarifying whether the lack of previous reports of C–C coupling over La 0.7 Sr 0.3 MnO 3–x (100) could be due to a “pressure gap”. Several types of experiments were performed at 400–800 K: flow experiments with a torr range reactant gas flown over La 0.7 Sr 0.3 MnO 3–x powders; ultra-high vacuum experiments with continuous gas exposures to a La 0.7 Sr 0.3 MnO 3–x (100) single-crystal sample; and torr range continuous gas exposures to a La 0.7 Sr 0.3 MnO 3–x (100) single-crystal sample. When ethanol and water were flown over La 0.7 Sr 0.3 MnO 3–x powders at 400–800 K, the products detected were ethene, acetaldehyde, acetone, crotonaldehyde, CO, CO 2 , and H 2 . Acetone was catalytically produced over both the La 0.7 Sr 0.3 MnO 3–x powder and the La 0.7 Sr 0.3 MnO 3–x (100) single-crystal sample at temperatures of 700–800 K when reaction conditions were on the order of 1 Torr of reactant gas and with an excess of water relative to ethanol (1 ethanol/9 water). Isotopic labeling with deuterium was used to gain insights into the C–C coupling reaction mechanism and paths in species with three and four carbons (C 3 and C 4 species). Additionally, steady-state isotopic transient kinetic analysis (SSITKA) experiments + simulations using carbon labeling of the ethanol feed were performed. Three mechanistic paths were considered for the C–C coupling step: the first two paths, A and B, involve coupling between two intermediates which are both in oxygen vacancies; and the third path, C, involves coupling between one intermediate in an oxygen vacancy and one intermediate outside of an oxygen vacancy. The results suggest that the dominant path to the C 3 product, acetone, depends on the conditions. The less active path (attributed to path A or B) occurs at 600–700 K and involves coupling between two irreversibly bound species. The more active path (attributed to path C) requires an excess of water, becomes dominant at 600–800 K, and involves coupling between one irreversibly bound species and one reversibly bound species. Based on these various observations from experiments and simulations, an elementary step is proposed for acetone formation involving a previously unreported C 4 transition state that is formed after aldol addition. Density functional theory calculations were performed based on this hypothesis, and it confirmed that this specific and previously unreported aldol addition path to acetone does exist and that this path consistent with the experimental data. In this path, C–C formation occurs to create a C 4 intermediate that is bound to an oxygen vacancy, then a hydrogen transfer with C–C bond breaking occurs that results in the production of the acetone molecule. The proposed mechanism is also consistent with the experimental observation that acetone formation has a greater than first-order dependence on the water vapor pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗