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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on B2(CN2)3 by Materials Project

B2(CN2)3 crystallizes in the trigonal R32 space group. The structure is two-dimensional and consists of three B2(CN2)3 sheets oriented in the (0, 0, 1) direction. B3+ is bonded in a trigonal planar geometry to three equivalent N3- atoms. All B–N bond lengths are 1.44 Å. C4+ is bonded in a linear geometry to two equivalent N3- atoms. Both C–N bond lengths are 1.22 Å. N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Materials Data on B2(CN2)3 by Materials Project

B2(CN2)3 crystallizes in the trigonal R-3c space group. The structure is two-dimensional and consists of six B2(CN2)3 sheets oriented in the (0, 0, 1) direction. B3+ is bonded in a trigonal planar geometry to three equivalent N3- atoms. All B–N bond lengths are 1.43 Å. C4+ is bonded in a linear geometry to two equivalent N3- atoms. Both C–N bond lengths are 1.22 Å. N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on B2(CN2)3 by Materials Project

B2(CN2)3 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two B2(CN2)3 sheets oriented in the (0, 0, 1) direction. B3+ is bonded in a trigonal planar geometry to three N3- atoms. All B–N bond lengths are 1.43 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a linear geometry to two equivalent N3- atoms. Both C–N bond lengths are 1.22 Å. In the second C4+ site, C4+ is bonded in a linear geometry to two N3- atoms. Both C–N bond lengths are 1.22 Å. There are three inequivalent N3- sites. In the first N3- site, N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom. In the second N3- site, N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom. In the third N3- site, N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Materials Data on B2(CN2)3 by Materials Project

B2(CN2)3 crystallizes in the triclinic P1 space group. The structure is one-dimensional and consists of two B2(CN2)3 ribbons oriented in the (0, 1, 0) direction. there are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three N3- atoms. There is one shorter (1.41 Å) and two longer (1.47 Å) B–N bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three N3- atoms. There is one shorter (1.41 Å) and two longer (1.47 Å) B–N bond length. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a linear geometry to two N3- atoms. Both C–N bond lengths are 1.23 Å. In the second C4+ site, C4+ is bonded in a linear geometry to two N3- atoms. Both C–N bond lengths are 1.21 Å. There are six inequivalent N3- sites. In the first N3- site, N3- is bonded in a bent 120 degrees geometry to one B3+ and one C4+ atom. The N–C bond length is 1.23 Å. In the second N3- site, N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom. In the third N3- site, N3- is bonded in a bent 120 degrees geometry to one B3+ and one C4+ atom. The N–C bond length is 1.23 Å. In the fourth N3- site, N3- is bonded in a bent 150 degrees geometry to one B3+ and one C4+ atom. In the fifth N3- site, N3- is bonded in a bent 120 degrees geometry to one B3+ and one C4+ atom. The N–C bond length is 1.23 Å. In the sixth N3- site, N3- is bonded in a bent 120 degrees geometry to one B3+ and one C4+ atom. The N–C bond length is 1.23 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evolution of B2 and laves phases in a ferritic steel under Fe 2+ ion irradiation at 475 °C

Microstructural evolution in a novel ferritic steel (Fe–12Cr–3W–3Ni–3Al–1Nb, in wt.%) computationally designed to contain B2 and Laves phases after 4 MeV Fe 2+ ion irradiation up to 220 dpa at 475 °C was characterized using transmission electron microscopy in conjunction with x-ray energy dispersive spectroscopy. The ferritic matrix phase exhibited dislocation loops and tangled dislocations, but our focus was on stability of two types of intermetallic precipitates. The B2–NiAl precipitates ~13 nm in size remained crystalline and appeared to have slightly lower Al concentration after irradiation. The Laves phase, (Fe,Cr) 2 (Nb,W), were present in two size ranges: coarse micron-scale precipitates which were amorphized with a slight composition change at irradiation doses above~30 dpa, while the finer precipitate particles~100 nm in size were partially disintegrated with a noticeable composition change at doses above~70 dpa. Meanwhile, many Nb/Cr-enriched particles ~8 nm in size formed within a few hundreds of nanometers from the disintegrated particles. The understanding of the phase stability would help design advanced steels and engineer microstructures that are stable against high irradiation doses, while retaining good high temperature strength.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Dynamics and structure of the B2→B19’ phase transformation in NiTi revealed through in situ 4D-STEM

The structural evolution of NiTi during the B2→B19’ martensitic phase transformation via thermal cycling is investigated using in situ four dimensional scanning transmission electron microscopy (4D-STEM). With 4D-STEM, we can directly visualize and quantify the nanoscale evolution of the martensitic structure on thermal cycling and also investigate the origin of diffuse scattering of NiTi in the pre-transitional state. Mapping of the martensite orientation and strain visualizes the progression of the transformation front and self-accommodation of the B19’ structure. Diffuse streaking and strain are measured in the pre-transitional austenite (B2) phase and demonstrate no localization or preferential directionality hinting that long-range homogeneous instability rather than nanoscale heterogeneities may be the origin of the pre-transitional anomalies in NiTi. Finally, it is revealed that NiTi does not reform the same martensite nanostructure on thermal cycling but does express similar features. This small variation is likely owing to transformation-induced dislocations.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Competitive B2 and B33 Nucleation during Solidification of Ni 50 Zr 50 Alloy: Molecular Dynamics Simulation and Classical Nucleation Theory

We studied the homogenous nucleation of the stoichiometric B2 and B33 phases in the Ni 50 Zr 50 alloy using the persistent embryo method and the classical nucleation theory. The two phases become very close competitors at large supercoolings, which is consistent with the experimental observations. In the case of the B2 phase, the linear temperature dependence of the solid–liquid interface (SLI) free energy extrapolated to the melting temperature leads to the same value as the one obtained from the capillarity fluctuation method (CFM). In the case of the B33 phases, the SLI free energy is also a linear function of temperature at large supercoolings, but the extrapolation to the melting temperature leads to a value which is considerably different from the CFM value. This is persistent with the large anisotropy of the SLI properties of the B33 phase nearby the melting temperature observed in the simulation of the nominally flat interface migration.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomic Layers of B2 CuPd on Cu Nanocubes as Catalysts for Selective Hydrogenation

The search for highly active and selective catalysts with high precious metal atom utilization efficiency has attracted increasing interest in both the fundamental synthesis of materials and important industrial reactions. Here, in this work, we report the synthesis of Pd–Cu nanocubes with a Cu core and an ordered B2 intermetallic CuPd shell with controllable atomic layers on the surface (denoted as Cu/B2 CuPd), which can efficiently and robustly catalyze the selective hydrogenation of acetylene (C 2 H 2 ) to ethylene (C 2 H 4 ) under mild conditions. The optimized Cu/B2 CuPd with a Pd loading of 9.5 at. % exhibited outstanding performance in the C 2 H 2 semi-hydrogenation with 100% C 2 H 2 conversion and 95.2% C 2 H 4 selectivity at 90 °C. We attributed this outstanding performance to the core/shell structure with a high surface density of active Pd sites isolated by Cu in the B2 intermetallic matrix, representing a structural motif of single-atom alloys (SAAs) on the surface. The combined experimental and computational studies further revealed that the electronic states of Pd and Cu are modulated by SAAs from the synergistic effect between Pd and Cu, leading to enhanced performance compared with pristine Pd and Cu catalysts. This study provides a new synthetic methodology for making single-atom catalysts with high precious metal atom utilization efficiency, enabling simultaneous tuning of both geometric and electronic structures of Pd active sites for enhanced catalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Endotaxially stabilized B2-FeSi nanodots in Si (100) via ion beam co-sputtering

We report on the formation of embedded B2-FeSi nanodots in [100]-oriented Si substrates, and investigate the crystallographic mechanism underlying the stabilization of this uncommon, bulk-unstable, phase. The nanodots were approximately 10 nm in size, and were formed by iron thin film deposition and subsequent annealing. Cross-sectional transmission electron microscopy, energy loss spectroscopy mapping, and quantitative image simulation and analysis were utilized to identify the phase, strain, and orientational relationship of the nanodots to the host silicon lattice. X-ray photoelectron spectroscopy was utilized to analyze the surface composition and local bonding. Elasticity calculations yielded a nanodot residual strain value of −18%. Geometrical phase analysis graphically pinpointed the positions of misfit dislocations, and clearly showed the presence of pinned (11{sup ¯}1{sup ¯}){sub Si}//(100){sub FeSi}, and unpinned (2{sup ¯}42){sub Si}//(010){sub FeSi}, interfaces. This partial endotaxy in the host silicon lattice was the mechanism that stabilized the B2-FeSi phase.

36 MATERIALS SCIENCE↗
DOE OSTI2014

B2+L2{sub 1} ordering in Co{sub 2}MnAl Heusler alloy

Magnetic and structural properties of B2 ordered Co{sub 2}MnAl Heusler alloy have been studied by X-ray diffraction and DC magnetization techniques. X-ray diffractogram shows the structure is of B2 type with preferential site disorder between Mn and Al atoms and presence of a small L2{sub 1} phase. DC magnetization studies at low temperature establish that the antiferromagnetic nature arises mainly due to the antiparallel coupling of spin moments of 3d electrons of Co with Mn atoms. Curie temperature (T{sub c}) is 733 K which is close to T{sub c} of the L2{sub 1} phase.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Structures of two intermediate phases between the B1 and B2 phases of PbS under high pressure

The structural transitions of PbS were investigated at pressures up to 50 GPa using synchrotron powder and single crystal X-ray diffraction (XRD) methods in diamond anvil cells. We found two intermediate phases between the B1 phase under atmospheric pressure and the B2 phase at 21.1 GPa, which is different to previous reports. The structures of these two intermediate phases were indexed as B27 and B33, respectively. Their structural parameters were investigated using density functional theory (DFT) calculations. Our results provide a new insight into understanding the transition pathway between the B1 and B2 phases in PbS.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Crystal orientation dependence of band matching in all-B2-trilayer current-perpendicular-to-plane giant magnetoresistance pseudo spin-valves using Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) Heusler alloy and NiAl spacer

We have experimentally investigated the crystal orientation dependence of band matching in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) pseudo-spin-valves using Co{sub 2}Fe(Ge{sub 0.5}Ga{sub 0.5}) (CFGG) Heusler alloy ferromagnetic layer and NiAl spacer. The high quality epitaxial CFGG/NiAl/CFGG all-B2-trilayers structure devices were fabricated on both MgO(001) and sapphire (112{sup ¯}0) single crystal substrates to create (001) and (110) crystal orientations. Same magneto-transport properties were observed from these two differently orientated devices indicating that there is no or little orientation dependence of band matching on MR output. We also found that all-B2-trilayer structure was free of lattice matching influence depending on the crystal orientation, which made it a good candidate for CPP-GMR device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Fabrication and characterization of spin injector using a high-quality B2-ordered-Co{sub 2}FeSi{sub 0.5}Al{sub 0.5}/MgO/Si(100) tunnel contact

We successfully fabricate a (100)-orientated B2-type-Co{sub 2}FeSi{sub 0.5}Al{sub 0.5} (CFSA)/MgO/Si(100) tunnel contact that is promising for an efficient spin injector for Si channels. The MgO barrier is formed by radical oxidation of an Mg thin film deposited on a Si(100) surface at room temperature and successive radical oxygen annealing at 400 °C. The CFSA electrode is grown on the MgO barrier at 400 °C by ultrahigh-vacuum molecular beam deposition, and it exhibits a (100)-orientated columnar polycrystalline structure with a high degree (63%) of B2-order. The MgO barrier near the interface of the CFSA/MgO junction is crystallized with the (100) orientation, i.e., the spin filter effect due to the MgO barrier could be expected for this junction. A three-terminal Si-channel spin-accumulation device with a CFSA/MgO/Si(100) spin injector is fabricated, and the Hanle effect of accumulated spin polarized electrons injected from this contact to the Si channel is observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Transmission electron microscopy studying of structural features of NiTi B2 phase formed under pulsed electron-beam impact

By transmission electron microscopy method the evolution of structural-phase states on a depth of close to equiatomic NiTi modified layer has been studied. Modification performed by pulse impact on its surface low-energy high-current electron beam (beam energy density 10 J/sm{sup 2}, 10 pulses, pulse duration 50mks). It is established that during the treatment in the layer thickness of 8–10 μm, the melting of primary B2 phase and contained therein as Ti2Ni phase particles occurs. The result is change in the concentration ratio of titanium and nickel in the direction of increasing titanium content, which was confirmed by X-ray analysis in the form of increased unit cell parameter B2 phase. Analysis of the electron diffraction pattern showed that the modified layer is characterized as a highly distorted structure on the basis of bcc lattice. Lattice distortions are maximal near the surface and extends to a depth of melt. In subjacent layer there is gradual decline lattice distortions is observed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

B2, B7 or B10: Which palm-based blend mandate wise to be chosen in Malaysia?

The diminishing fossil energy resources, coupled with heightened interest in the abatement of greenhouse gas emissions and concerns about energy security have motivated Malaysia to produce palm-based biodiesel and it has been started to be exported since 2006. In line with this issue, the government in Malaysia launched the palm-based biodiesel blending mandate of five percent (B5) in the federal administration of Putrajaya on 1{sup st} June 2011. This was then followed by four states: Malacca on July 11, Negeri Sembilan on August 1, Kuala Lumpur on September 1 and Selangor on October 1 of the same year but it is yet to be implemented nationwide. However what is the wise blend mandate to be chosen? Thus, this paper seeks to examine the possible impact of various blend mandates implementation (B2, B7 and B10) on the palm oil industry market variables (stock and price) since the main aim of biodiesel industry in Malaysia is to reduce domestic palm oil stock to below one million tones and provide a floor price to support Crude Palm Oil (CPO) prices at RM2,000 per tonne. A structural econometric model consisting of nine structural equations and three identities was proposed in this study. The model has been estimated by two stage least squares (2SLS) method using annual data for the period 1976-2013. The study indicates that counterfactual simulation of a decrease from B5 to B2 predicts a decrease (11.2 per cent) in CPO domestic consumption for biodiesel usage, 731.02 per cent reduction in CPO stock and an increase of 27.41 percent in domestic price of CPO. However the increase in the blend mandate from B5 to B7 and B10 suggest that domestic consumption of CPO for biodiesel purpose increase 7.40 and 18.55 percent respectively. The interesting findings in this study suggest that no matter whether Malaysian government increase or decrease the blend mandate the increase in the price of CPO are the same with an increase of is 27.41 percent. Hence, this study suggests that the lower blend mandate is the most favourable on.+-e compared to increasing it in this short period due to high production cost of CPO prices. However, future study on economic feasibility of palm-based biodiesel has to be conducted to support this study.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2023

PBE-GGA predicts the B8↔B2 phase boundary of FeO at Earth’s core conditions

FeO is a crucial component of the Earth’s core, and its thermodynamic properties are essential to developing more accurate core models. It is also a notorious correlated insulator in the NaCl-type (B1) phase at ambient conditions. It undergoes two polymorphic transitions at 300 K before it becomes metallic in the NiAs-type (B8) structure at ~100 GPa. Although its phase diagram is not fully mapped, it is well established that the B8 phase transforms to the CsCl-type (B2) phase at core pressures and temperatures. Here, we report a successful ab initio calculation of the B8↔B2 phase boundary in FeO at Earth’s core pressures. We show that fully anharmonic free energies computed with the Perdew–Burke–Ernzerhof-generalized gradient approximation coupled with thermal electronic excitations reproduce the experimental phase boundary within uncertainties at P > 255 GPa, including the largely negative Clapeyron slope of –52 MPa/K. This study validates the applicability of a standard density functional theory functional to FeO under Earth’s core conditions and demonstrates the theoretical framework that enables complex predictive studies of this region.

58 GEOSCIENCES↗
DOE OSTI2011

IONIZED GAS KINEMATICS AND MORPHOLOGY IN Sgr B2 Main ON 1000 AU SCALES

We have imaged the Sgr B2 Main region with the Very Large Array in the BnA configuration ({theta}{sub beam} = 0.''13) in both the H52{alpha} (45.453 GHz) radio recombination line and 7 mm continuum emission. At a distance of 8500 pc, this spatial resolution corresponds to a physical scale of 0.005 pc ({approx}1100 AU). The current observations detect H52{alpha} emission in 12 individual ultracompact and hypercompact H II regions. Two of the sources with detected H52{alpha} emission have broad ({Delta}V{sub FWHM} {approx} 50 km s{sup -1}) recombination lines, and two of the sources show lines with peaks at more than one velocity. We use line parameters from the H52{alpha} lines and our previous H66{alpha} line observations to determine the relative contribution of thermal, pressure, and kinematic broadening, and electron density. These new observations suggest that pressure broadening can account for the broad lines in some of the sources, but that gas motions (e.g., turbulence, accretion, or outflow) contribute significantly to the broad lines in at least one of the sources (Sgr B2 F3).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

SAGITTARIUS B2 MAIN: A CLUSTER OF ULTRA-COMPACT H II REGIONS AND MASSIVE PROTOSTELLAR CORES

The ionized core in the Sgr B2 Main star-forming region was imaged using the Submillimeter Array archival data observed for the H26{alpha} line and continuum emission at 0.86 mm with an angular resolution 0.''3. Eight hyper-compact H26{alpha} emission sources were detected with a typical size in the range of 1.6-20 Multiplication-Sign 10{sup 2} AU and electron density of 0.3-3 Multiplication-Sign 10{sup 7} cm{sup -3}, corresponding to the emission measure 0.4-8.4 Multiplication-Sign 10{sup 10} cm{sup -6} pc. The H26{alpha} line fluxes from the eight hyper-compact H II sources imply that the ionization for each of the sources must be powered by a Lyman continuum flux from an O star or a cluster of B stars. The most luminous H26{alpha} source among the eight detected sources requires an O6 star that appears to be embedded in the ultra-compact H II region F3. In addition, {approx}23 compact continuum emission sources were also detected within the central 5'' Multiplication-Sign 3'' ({approx}0.2 pc) region. Under the assumption of a power-law distribution for the dust temperature, with the observed brightness temperature of the dust emission we determined the physical properties of the submillimeter emission sources, showing that the molecular densities are in the range of 1-10 Multiplication-Sign 10{sup 8} cm{sup -3}, surface densities between 13 and 150 g cm{sup -2}, and total gas masses in the range from 5 to {approx}> 200 M{sub Sun }, which are one or two orders of magnitude greater than the corresponding values of the Bonnor-Ebert mass. With a mean free-fall timescale of 2 Multiplication-Sign 10{sup 3} years, each of the massive protostellar cores is undergoing gravitational collapse to form new massive stars in the Sgr B2 Main core.

79 ASTRONOMY AND ASTROPHYSICS↗