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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A step towards unveiling the nature of three cataclysmic variables: LS Cam, V902 Mon, and SWIFT J0746.3-1608

ABSTRACT We have carried out detailed time-resolved timing analyses of three cataclysmic variables (CVs) namely LS Cam, V902 Mon, and SWIFT J0746.3-1608, using the long-baseline, high-cadence optical photometric data from the Transiting Exoplanet Survey Satellite. Our analysis of LS Cam observations hints the presence of a superorbital period of ∼4.025 ± 0.007 d along with negative and positive superhump periods of ∼3.30 and 3.70 h, respectively. These results can be explained as an interaction of nodal and apsidal precession of the accretion disc with orbital motion. For the other two sources, V902 Mon and SWIFT J0746.3-1608, we have found evidence of a beat period of 2387.0 ± 0.6 and 2409.5 ± 0.7 s, respectively, which were not found in earlier studies. Our results presented in this study indicate the change in the accretion mode during the entire observing period for both sources. For V902 Mon, an apparent orbital period derivative of (6.09 ± 0.60) × 10−10 was also found. Moreover, the second harmonic of orbital frequency dominates the power spectrum of SWIFT J0746.3-1608, suggestive of ellipsoidal modulation of the secondary star. Present analyses suggest that LS Cam could be a superhumping CV, whereas V902 Mon and SWIFT J0746.3-1608 are likely to be variable disc-overflow accreting intermediate polars.

Rawat, Nikita (ORCID:0000000246336832)↗
DOE OSTI2020

Effect of Co 2 N impurity on the superconducting properties of δ-MoN thin films grown by polymer assisted deposition

We report the effect of Co 2 N impurity on the superconducting properties of δ-MoN thin films grown by polymer-assisted deposition on c-cut sapphire (Al 2 O 3 ). The films show a superconducting transition temperature of 10.4 K and an upper critical field H c2 (0) perpendicular to the film surface around 3 T. The latter corresponds to a relatively large coherence length ξ, which enhances the two-dimensional limit when the magnetic field is applied parallel to the film surface. In comparison with pure δ-MoN films, the inclusion of Co 2 N impurity in the δ-MoN films could significantly modify the critical current density at the vortex-free state. In conclusion, the ability to tune the superconducting properties of metal-nitride superconductors by introducing chemically and structurally compatible impurity may find potential applications for superconducting single-photon detectors.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN crystallizes in the hexagonal P6/mmm space group. The structure is two-dimensional and consists of one MoN sheet oriented in the (0, 0, 1) direction. Mo3+ is bonded in a 6-coordinate geometry to six equivalent N3- atoms. All Mo–N bond lengths are 2.32 Å. N3- is bonded in a 9-coordinate geometry to six equivalent Mo3+ and three equivalent N3- atoms. All N–N bond lengths are 1.96 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two MoN sheets oriented in the (0, 0, 1) direction. Mo3+ is bonded in a distorted square co-planar geometry to four equivalent N3- atoms. There are a spread of Mo–N bond distances ranging from 2.07–2.12 Å. N3- is bonded in a distorted square co-planar geometry to four equivalent Mo3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN crystallizes in the hexagonal P6/mmm space group. The structure is one-dimensional and consists of one MoN ribbon oriented in the (0, 0, 1) direction. Mo3+ is bonded in a linear geometry to two equivalent N3- atoms. Both Mo–N bond lengths are 1.91 Å. N3- is bonded in a linear geometry to two equivalent Mo3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo3+ is bonded to four equivalent N3- atoms to form corner-sharing MoN4 tetrahedra. All Mo–N bond lengths are 2.02 Å. N3- is bonded to four equivalent Mo3+ atoms to form corner-sharing NMo4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Mo3+ is bonded in a body-centered cubic geometry to eight equivalent N3- atoms. All Mo–N bond lengths are 2.34 Å. N3- is bonded in a body-centered cubic geometry to eight equivalent Mo3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN is Tungsten Carbide structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Mo3+ is bonded to six equivalent N3- atoms to form a mixture of distorted corner, edge, and face-sharing MoN6 pentagonal pyramids. All Mo–N bond lengths are 2.19 Å. N3- is bonded to six equivalent Mo3+ atoms to form a mixture of distorted corner, edge, and face-sharing NMo6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Mo3+ is bonded to six equivalent N3- atoms to form a mixture of edge and corner-sharing MoN6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Mo–N bond lengths are 2.18 Å. N3- is bonded to six equivalent Mo3+ atoms to form a mixture of edge and corner-sharing NMo6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. Mo3+ is bonded in a rectangular see-saw-like geometry to four equivalent N3- atoms. There are one shorter (2.00 Å) and three longer (2.06 Å) Mo–N bond lengths. N3- is bonded in a distorted rectangular see-saw-like geometry to four equivalent Mo3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN is Tungsten Carbide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mo3+ is bonded to six equivalent N3- atoms to form a mixture of edge, face, and corner-sharing MoN6 octahedra. The corner-sharing octahedral tilt angles are 45°. All Mo–N bond lengths are 2.19 Å. N3- is bonded to six equivalent Mo3+ atoms to form a mixture of distorted edge and corner-sharing NMo6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoN by Materials Project

MoN is Tungsten Carbide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Mo3+ sites. In the first Mo3+ site, Mo3+ is bonded to six equivalent N3- atoms to form a mixture of distorted corner, edge, and face-sharing MoN6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 44°. All Mo–N bond lengths are 2.16 Å. In the second Mo3+ site, Mo3+ is bonded to six equivalent N3- atoms to form a mixture of corner, edge, and face-sharing MoN6 octahedra. All Mo–N bond lengths are 2.22 Å. N3- is bonded to six Mo3+ atoms to form a mixture of distorted corner, edge, and face-sharing NMo6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Steam-Assisted Ammonolysis of MoO2 as a Synthetic Pathway to Oxygenated δ-MoN

A common route for the synthesis of molybdenum nitrides is through the temperature-programmed reaction of molybdenum oxides with NH3, or ammonolysis. In this work, the role of precursor phase, gas phase chemistry (impact of H2O), and temperature profile on the reaction outcome (700 °C) was examined, which resulted in varying amounts of MoO2, H2MoO5, and the nitride phases—cubic γ (nominally Mo2N) and hexagonal δ (nominally MoN). The phase fraction of the δ phase increased with precursor in the sequence MoO2 > MoO3 > H2MoO5. Steam in the reaction gas also favored the production of δ over γ, but with too much steam, MoO2 was obtained in the product. Synthesis conditions for obtaining nearly phase-pure δ were identified: MoO2 as the precursor, 2% H2O in the gas stream, and a moderate heating rate (3 °C/min). In situ X-ray diffraction provided insights into the reaction pathway. Extensive physico-chemical analysis of the δ phase, including synchrotron X-ray and neutron diffraction, electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and prompt gamma activation analysis, revealed its stoichiometry to be MoO0.108(8)N0.892(8)H0.012(5), indicating non-trivial oxygen incorporation. The presence of N/O ordering and an impurity phase Mo5N6 were also revealed, detectable only by neutron diffraction. Notably, a computationally predicted MoON phase (doi: 10.1103/PhysRevLett.123.236402), of interest due to its potential to display a metal-insulator transition, did not appear under any reaction condition examined.

Pandey, Shobhit↗
DOE OSTI2022

DFT Investigation of Ammonia Formation via a Langmuir–Hinshelwood Mechanism on Mo-Terminated δ-MoN(0001)

In this work, we employed density functional theory to elucidate the energetics associated with elementary steps along a Langmuir-Hinshelwood mechanism for the Haber-Bosch synthesis of ammonia from N 2 and H 2 on a hexagonal, Mo-terminated molybdenum nitride surface. Using nudged elastic band calculations, we determined the energy barriers involved in the reaction processes. An active site consisting of four nearest-neighbor Mo atoms, previously identified as an active site on similar surfaces, was chosen to investigate the reaction processes. Using this approach, we calculate a barrier of ~0.5 eV for the dissociation of N 2 . The superior activity of the dissociation of the strong N 2 bonds is rationalized based on the unique geometric and electronic configurations present at these active sites. Despite the favorable energetics for nitrogen dissociation, the energy cost for hydrogenation of NH x (0 ≤ x ≤ 2) species is shown to be energetically limiting for the formation of ammonia through the Langmuir-Hinshelwood mechanism at these sites, with elementary step activation barriers calculated to be as large as ~2 eV. A comparison to Haber-Bosch results derived from a similar γ-Mo 2 N model system suggests the relative independence of surface chemistry and bulk stoichiometry for rhombic Mo 4 active sites present on molybdenum nitrides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

The Ice Particle and Aggregate Simulator (IPAS). Part III: Verification and Analysis of Ice–Aggregate and Aggregate–Aggregate Collection for Microphysical Parameterization

Abstract The Ice Particle and Aggregate Simulator (IPAS) is used to theoretically represent the aggregation process of ice crystals. Aggregates have a variety of formations based on initial ice particle size, shape, and falling orientation, all of which influence water phase partitioning. Aggregate dimensional properties and density changes are calculated for monomer–monomer (MON–MON), monomer–aggregate (MON–AGG), and aggregate–aggregate (AGG–AGG) collection to be used by ice-microphysical models for improvement in aggregation parameterizations. Aggregates are chosen from a database of 9 744 000 preformed combinations to be further collected (see Part II). AGG–AGG collection results in more extreme and a smaller range of aggregate aspect ratios than MON–AGG collection. A majority of aggregates are closer to prolate than oblate spheroids, regardless of collection type, except for quasi-horizontally oriented particles that have extreme aspect ratios to begin with. MON–AGG collection frequently results in an increase in density upon collection, whereas MON–MON and AGG–AGG collection almost always result in particle density decreases, with extreme reductions near 99% for MON–MON collection. MON–MON collection results in the greatest decreases in density but then quickly becomes unaffected by the addition of more monomers due to inherent size differences between monomers and aggregates. Finally, a holistic analysis to in situ observations of cloud particle images is presented. IPAS 2D aspect ratios surround a median value of 0.6 and closely follow that of previous studies while varying by no more than ≈12% on average from observed aggregates.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Production and Fuel properties of Iso-Olefins with Controlled Molecular Structure and Obtained from Butene Oligomerization

The ability to control the molecular structure (e.g., degree of branching) of iso-olefins produced from oligomerizing light olefins is a valuable tool for tuning the final compositions of hydrocarbon fuels and targeting specific fuel properties. In this study, we demonstrated that the degree of branching of iso-olefins obtained from butene(s) oligomerization can be controlled by tuning process conditions (i.e., temperature, weight hourly space velocity [WHSV], and nature of butene feedstock) and by choosing the proper catalyst (i.e., Amberlyst-36 vs. Y/ZSM-22). In this study, we produced three types of iso-olefin mixtures: 1) a methyl-heptenes rich (74 wt.%) mixture, 2) dimethyl-hexenes rich (80–96 wt.%) mixtures, and 3) highly branched (i.e., more than three methyl substitutions) iso-olefins rich (>50 wt.%) mixtures. While dimethyl-hexenes are preferentially formed at lower temperatures (60–100°C) and WHSV (i.e., 2 hr-1), methyl-heptenes are favorably produced at higher temperatures (>100°C) and WHSVs (i.e., 7 hr-1) over Amberlyst-36. The use of either 1-butene or 2-butene as feedstock resulted in liquid products with similar branching because facile intramolecular isomerization occurs prior to oligomerization. However, the use of isobutylene feedstock forms a significantly more branched olefin product. The formation of highly branched iso-olefins also is favored at higher temperature (140°C) over Amberlyst-36. Using Y/ZSM-22 instead of Amberlyst-36 allowed preferential formation of less-branched methyl-heptenes. For each type of iso-olefins mixture, we determined fuel properties including research octane number (RON), motor octane number (MON), and octane sensitivity (S), which is the difference between RON and MON. We found that not only RON and MON but also S values increased with the degree of branching of these complex mixtures of iso-olefins. The highest RON of 99.7 and S value of 9.3 were obtained for a mixture of highly branched iso-olefins.

Dagle, Vanessa↗