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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Feld-induced modulation of two-dimensional electron gas at LaAlO 3 /SrTiO 3 interface by polar distortion of LaAlO 3

Since the discovery of two-dimensional electron gas at the LaAlO 3 /SrTiO 3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO 3 /SrTiO 3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO 3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO 3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lithium calix[4]arenes: structural studies and use in the ring opening polymerization of cyclic esters

We have structurally characterized a number of lithiated calix[4]arenes, where the bridge in the calix[4]arene is thia (–S–, L S H 4 ), sulfinyl (–SO–, L SO H 4 ), sulfonyl (–SO 2 –, L SO2 H 4 ), dimethyleneoxa (–CH 2 OCH 2 –, L COC H 4 ) or methylene (–CH 2 –, LH 4 ). In the case of L 4S H 4 , interaction with LiO t Bu led to the isolation of the complex [Li 8 (L 4S ) 2 (THF) 4 ]·5THF ( 1 ·5THF), whilst similar interaction of L 4SO H 4 led to the isolation of [Li 6 (L 4SO H) 2 (THF) 2 ]·5(THF) ( 2 ·5THF). Interestingly, the mixed sulfinyl/sulfonyl complexes [Li 8 (calix[4]arene(SO)(SO 2 )(SO 1.68 ) 2 ) 2 (THF) 6 ]·8(THF) ( 3 ·8THF) and [Li 5 Na(L SO/3SO2 H) 2 (THF) 5 ]·7.5(THF) ( 4 ·7.5(THF) have also been characterized. Interaction of LiO t Bu with L SO2 H 4 and L COC H 4 afforded [Li 5 L 4SO2 (OH)(THF) 4 ]·2THF ( 5 ·2THF) and [Li 6 (L COC ) 2 (HO t Bu) 2 ]·0.78THF·1.22hexane ( 6 ·0.78THF·1.22hexane), respectively. In the case of LH 4 , reaction with LiO t Bu in THF afforded a monoclinic polymorph [LH 2 Li 2 (thf)(OH 2 ) 2 ]·3THF ( 7 ·3THF) of a known triclinic form of the complex, whilst reaction of the de-butylated analogue of LH 4 , namely de-BuLH 4 , afforded a polymeric chain structure {[Li 5 (de-BuL)(OH)(NCMe) 3 ]·2MeCN} n ( 8 ·2MeCN). For comparative catalytic studies, the complex [Li 6 (L Pr ) 2 (H 2 O) 2 ]·hexane ( 9 hexane), where L Pr2 H 2 = 1,3-di- n -propyloxycalix[4]areneH 2 , was also prepared. The molecular crystal structures of 1–9 are reported, and their ability to act as catalysts for the ring opening (co-)/polymerization (ROP) of the cyclic esters ε-caprolactone, δ-valerolactone, and rac -lactide has been investigated. In most of the cases, complex 6 outperformed the other systems, allowing for higher conversions and/or greated polymer M n .

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

Crystal and magnetic structure of polar oxide HoCrWO 6

In this study, polar magnetic oxide HoCrWO 6 is synthesized and its crystal structure, magnetic structure, and thermodynamic properties are investigated. HoCrWO 6 forms the polar crystal structure (space group Pna 2 1 (#33)) due to the cation ordering of W 6+ and Cr 3+ . There is an antiferromagnetic transition at T N = 24.5 K along with the magnetic entropy change (~5 J.Kg. –1 K –1 at 70 kOe). Neutron diffraction measurement indicates that both Cr and Ho sublattices are ordered with the moment of 2.32(5)μ B and 8.7(4)μ B at 2 K, respectively. While Cr forms A-type collinear antiferromagnetic (AFM) structure with magnetic moment along the b axis, Ho sublattice orders in a non-coplanar AFM arrangement. A comparison with isostructural DyFeWO 6 and DyCrWO 6 indicates that the magnetic structure of this family of compounds is controlled by the presence or absence of e g electrons in the transition metal sublattice.

42 ENGINEERING↗
DOE OSTI2020

Materials Data on HoC3S3(O2F)9 by Materials Project

HoO9(CF3)3(SO3)3 crystallizes in the hexagonal P6_3/m space group. The structure is zero-dimensional and consists of six fluoroform molecules, six sulfur trioxide molecules, and two HoO9 clusters. In each HoO9 cluster, Ho is bonded in a 9-coordinate geometry to nine O atoms. There are six shorter (2.30 Å) and three longer (2.31 Å) Ho–O bond lengths. There are two inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Ho atom. In the second O site, O is bonded in a single-bond geometry to one Ho atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Spin Wave Excitations in Honeycomb Antiferromagnet MnTiO 3

Using inelastic neutron scattering, we investigate the spin wave excitations on the antiferromagnetic MnTiO 3 (T N = 65 K), which has the stacked honeycomb structure. At T = 2 K, the spin wave energy extends up to 10.7 meV with the zone-center anisotropy gap of 0.8 meV. Whereas the dispersion is also strong along the direction perpendicular to the honeycomb planes, the exchange cancellation causes the magnetic interactions to be effectively anisotropic below TN. Furthermore, while the spin wave spectrum survives at temperatures above TN, we find that the magnetic interactions become more anisotropic within the paramagnetic phase. These results suggest that the magnetic interaction in MnTiO 3 crosses over from being three dimensional to two dimensional above T N .

36 MATERIALS SCIENCE↗
NASA NTRS1988

Windshear avoidance - Requirements and proposed system for airborne lidar detection

A generalized windshear hazard index is derived from considerations of wind conditions and an aircraft's present and potential altitude. Based on a systems approach to the windshear threat, lidar appears to be a viable methodology for windshear detection and avoidance, even in conditions of moderately heavy precipitation. The airborne CO2 and Ho:YAG lidar windshear detection systems analyzed can each give the pilot information about the line-of-sight component of windshear threat from his present position to a region extending 1 to 3 km in front of the aircraft. This constitutes a warning time of 15 to 45 s. The technology necessary to design, build and test such a brassboard 10.6-micron CO2 lidar is at hand.

Targ, Russell↗
DOE OSTI2020

Materials Data on HoSeO3F by Materials Project

HoSeO3F crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ho3+ is bonded in a 8-coordinate geometry to six O2- and two equivalent F1- atoms. There are a spread of Ho–O bond distances ranging from 2.29–2.64 Å. There are one shorter (2.20 Å) and one longer (2.21 Å) Ho–F bond lengths. Se4+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.71–1.78 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Se4+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ho3+ and one Se4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three equivalent Ho3+ and one Se4+ atom. F1- is bonded in a distorted bent 120 degrees geometry to two equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaHoFe4O7 by Materials Project

BaHoFe4O7 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ba2+ is bonded to twelve equivalent O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, edges with twelve equivalent FeO4 tetrahedra, and faces with four equivalent HoO6 octahedra. All Ba–O bond lengths are 3.24 Å. Ho3+ is bonded to six equivalent O2- atoms to form HoO6 octahedra that share corners with twelve equivalent FeO4 tetrahedra and faces with four equivalent BaO12 cuboctahedra. All Ho–O bond lengths are 2.26 Å. Fe+2.25+ is bonded to four O2- atoms to form FeO4 tetrahedra that share corners with three equivalent HoO6 octahedra, corners with six equivalent FeO4 tetrahedra, and edges with three equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 51°. There are three shorter (1.98 Å) and one longer (2.10 Å) Fe–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ba2+, one Ho3+, and two equivalent Fe+2.25+ atoms. In the second O2- site, O2- is bonded in a tetrahedral geometry to four equivalent Fe+2.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Te5O13 by Materials Project

Ho2Te5O13 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one Ho2Te5O13 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.21–2.81 Å. In the second Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.30–2.64 Å. There are five inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.91–2.46 Å. In the second Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.88–2.54 Å. In the third Te4+ site, Te4+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Te–O bond distances ranging from 1.90–1.94 Å. In the fourth Te4+ site, Te4+ is bonded in a 5-coordinate geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.90–2.75 Å. In the fifth Te4+ site, Te4+ is bonded in a rectangular see-saw-like geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.89–2.15 Å. There are thirteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Te4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ho3+ and one Te4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two Te4+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two Te4+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to one Ho3+ and one Te4+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two Te4+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+ and two Te4+ atoms. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to two Ho3+ and one Te4+ atom. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to two Te4+ atoms. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+ and one Te4+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Te4+ atoms. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. In the thirteenth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ho3+ and one Te4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Understanding how chemical structure affects ignition-delay-time $\phi$-sensitivity

$\phi$-sensitivity is the change in ignition delay time (IDT) with respect to the fuel-to-air equivalence ratio ($\phi$). High $\phi$-sensitivity is a desirable fuel property for applications in advanced compression ignition and multi-mode engine designs. Understanding how $\phi$-sensitivity depends on chemical structure is essential for selecting promising biofuels from the ever-growing list of proposed candidates. Here, we investigate the effect of chemical structure on $\phi$-sensitivity with experiment, simulation, and theory. Experimental Advanced Fuel Ignition Delay Analyzer (AFIDA) measurements for 2,4-dimethylpentane and diisopropyl ether provide evidence that branching and functional groups strongly impact $\phi$-sensitivity. Further insights into this dependence are obtained with 0-D kinetic simulations with existing mechanisms for n-pentane, diethyl ether, 3-pentanone, n-heptane, 2-methylhexane, 2,4-dimethylpentane, and 2,2,3-trimethylbutane. Quantum mechanical (QM) G4 calculations of low-temperature reactions help explain the observed experimental and simulation trends. Specifically, these QM calculations provide theoretical estimates of the ketohydroperoxide (KHP) dissociation rates, the HO 2 formation rates from peroxy radical (ROO), and the “cross-over” temperatures, i.e., the temperature at which ROO dissociation is favored compared to hydroperoxyl radical (QOOH) formation. Each of these reaction rates is compared to the n-alkane reference point to determine the impact of branching and different functional groups. Although kinetic mechanisms typically assume that KHP dissociation rates are invariant of chemical environment, our QM results suggest that this rate can span a range of roughly two orders of magnitude. We also discuss the importance of including the peroxy-hydroperoxy (OO-OOH) hydrogen transfer reaction for branched ethers. Finally, the insights gained assist in proposing a highly $\phi$-sensitive compound, namely, isopropyl propyl ether.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

Investigation of airborne lidar for avoidance of windshear hazards

A generalized windshear hazard index is defined, which is derived from considerations of wind conditions at the present position of an aircraft and from remotely sensed information along the extended flight path. Candidate airborne sensor technologies based on microwave Doppler radar, Doppler lidar, and infrared radiometric techniques are discussed in the context of overall system functional requirements. Initial results of a performance and technology assessment study for competing lidars are presented. Based on a systems approach to the windshear threat, lidar appears to be a viable technology for windshear detection and avoidance, even in conditions of moderately heavy precipitation. The proposed airborne CO2 and Ho:YAG lidar windshear-detection systems analyzed here can give the pilot information about the line-of-sight component of windshear threat from his present position to a region extending 1 to 3 km in front of the aircraft. This constitutes a warning time of 15 to 45 seconds. The technology necessary to design, build, and test such a brassboard 10.6 micron CO2 lidar is now available. However, for 2-micron systems, additional analytical and laboratory investigations are needed to arrive at optimum 2-micron rare-earth-based laser crystals.

Targ, Russell↗
DOE OSTI2024

Magnetic functionalization and catalytic behavior of magnetic nanoparticles during laser photochemical graphitization of polyimide

We report laser-assisted photochemical graphitization of polyimides (PIs) into functional magnetic nanocomposites using laser irradiation of PI in the presence of magnetite nanoparticles (MNPs). PI Kapton sheets covered with MNP were photochemically treated under ambient conditions using a picosecond pulsed laser (1064 nm) to obtain an electrically conductive material. Scanning electron microscopy of the treated material revealed a layered magnetic nanoparticle/graphite (MNP/graphite) nanocomposite structure. Four probe conductivity measurements indicated that the nanocomposite has an electrical conductivity of 1550 ± 60 S/m. Superconducting quantum interference device magnetometer-based magnetic characterization of the treated material revealed an anisotropic ferromagnetic response in the MNP/graphite nanocomposite compared to the isotropic response of MNP. Raman spectroscopy of the MNP/graphite nanocomposite revealed a fourfold improvement in graphitization, suppression in disorder, and decreased nitrogenous impurities compared to the graphitic material obtained from laser treatment of just PI sheets. X-ray photoelectron spectroscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy were used to delineate the phase transformations of MNP during the formation of MNP/graphite nanocomposite. Post-mortem characterization indicates a possible photocatalytic effect of MNP during MNP/graphite nanocomposite formation. Under laser irradiation, MNP transformed from the initial Fe 3 O 4 phase to γ-Fe 2 O 3 and Fe 5 C 2 phases and acted as nucleation spots to catalyze the graphitization process of PI.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Complex-coordinate calculation of (1,3)P resonances in Ps(-) using Hylleraas functions

An accurate calculation for (1,3)P autodetaching resonances in Ps(-) has been carried out using the complex-rotation method, which has the advantage of giving resonance position and width at the same time. The wave function is of the Hylleraas type with an available number of terms up to 1140. One 1P and two 3P resonances below the n = 2 threshold and two 1P and two 3P resonances below the n = 3 threshold of the positronium atom. Resonance parameters are compared with those obtained from scattering and adiabatic calculations where available.

Bhatia, A. K.↗
NASA NTRS1994

The rotating molecular core in G10.6 - 0.4: Synthesis maps in (12)C(18)O

Using the Owens Valley Radio Observatory millimeter-wave interferometer, the compact molecular cloud core surrounding the H II region G10.60-0.4 has been resolved in the C(18)O J = 1-0 transition. Since this line is most likely optically thin, it is an excellent tracer of the total column density. We find a centrally condensed and flattened (12.6 sec x 4.2 sec ; 0.3 pc x 0.1 pc) core, which is rotating rapidly with a substantial velocity gradient (17 +/- 2 km/s pc) along the major axis. The core is quite bright (greater than 10K), dense (greater than (10(exp 6)/cu cm), massive (10(exp 3) solar mass), and embedded in a more extended (greater than 60 seconds) envelope. There is no evidence for absorption, implying that the C(18)O emitting gas is both optically thin and substantially hotter than the equivalent continuum temperature at 3 mm. The systemic velocity of the rotating core is -2.5 +/- 0.5 km/s, the same as the systemic velocity of the extended cloud.

Ho, Paul T. P.↗
DOE OSTI2020

Materials Data on Ho2MgSe4 by Materials Project

MgHo2Se4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mg2+ is bonded to five Se2- atoms to form MgSe5 square pyramids that share corners with four HoSe6 octahedra, edges with four HoSe6 octahedra, and edges with four equivalent MgSe5 square pyramids. The corner-sharing octahedra tilt angles range from 3–4°. There are a spread of Mg–Se bond distances ranging from 2.67–2.76 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share corners with three equivalent HoSe6 octahedra, corners with two equivalent MgSe5 square pyramids, edges with six HoSe6 octahedra, and an edgeedge with one MgSe5 square pyramid. The corner-sharing octahedra tilt angles range from 53–58°. There are a spread of Ho–Se bond distances ranging from 2.82–2.94 Å. In the second Ho3+ site, Ho3+ is bonded to six Se2- atoms to form HoSe6 octahedra that share corners with three equivalent HoSe6 octahedra, corners with two equivalent MgSe5 square pyramids, edges with four HoSe6 octahedra, and edges with three equivalent MgSe5 square pyramids. The corner-sharing octahedra tilt angles range from 53–58°. There are a spread of Ho–Se bond distances ranging from 2.76–2.95 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three equivalent Mg2+ and two equivalent Ho3+ atoms to form a mixture of edge and corner-sharing SeHo2Mg3 square pyramids. In the second Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three Ho3+ atoms. In the fourth Se2- site, Se2- is bonded to two equivalent Mg2+ and three Ho3+ atoms to form SeHo3Mg2 square pyramids that share corners with two equivalent SeHo2Mg3 square pyramids and edges with five SeHo3Mg2 square pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbHo(MoO4)2 by Materials Project

RbHo(MoO4)2 crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Rb1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Rb–O bond distances ranging from 2.85–3.08 Å. Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.28–2.58 Å. Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Mo–O bond distances ranging from 1.76–1.86 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Rb1+, one Ho3+, and one Mo6+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Rb1+ and one Mo6+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ho3+ and one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Local ordering in disordered Nd x Zr 1-x O 2-0.5x pyrochlore as observed using neutron total scattering

Pyrochlore complex oxides (A 2 B 2 O 7 ) are an important class of fluorite-derivative ceramics with exceptional chemical and structural versatility which make them ideal model systems for studying disordering mechanisms over a range of spatial scales. Here, neutron total scattering methods were used to analyze the structural behavior in the non-stoichiometric series Nd x Zr 1-x O 2-0.5x (0.5 ≤ x ≤ 0.23) as a function of Nd content, x. Characterization of the structure functions using Rietveld refinement and the pair distribution functions with small-box refinement reveal complex disordering pathways; the average, long-range phase changes over a very narrow compositional range from pyrochlore ($Fd\bar{3}m$) to defect fluorite ($Fm\bar{3}m$) through full randomization of the cation and anion sublattices at x ~ 0.31, while the local, short-range structure continuously adopts a weberite-type atomic arrangement (C222 1 ). Comparison to a previously studied Ho 2 Ti 2-x Zr x O 7 solid solution series reveals how changes in chemical composition and stoichiometry modify defect formation and determine how disordering progresses across different length scales in pyrochlore oxides.

36 MATERIALS SCIENCE↗