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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The nightside ionosphere of Venus under varying levels of solar EUV flux

Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter (PVO), and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV flux effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.

Ho, C. M.↗
NASA NTRS1993

The Nightside Ionosphere of Venus Under Varying Levels of Solar EUV Flux

Solar activity varied widely over the 14 year lifetime of the Pioneer Venus Orbiter, and these variations directly affected the properties of the nightside ionosphere. At solar maximum, when solar EUV was largest, the Venus ionosphere was found to extend to highest altitudes and nightward ion transport was the main source of the nightside ionosphere. At solar minimum, nightward ion transport was reduced, and electron precipitation was thought to be the main source. In this study, we have attempted a separation of spatial variations from temporal variations by examining the altitude profiles of the magnetic field, and electron density and temperature for three different solar EUV flux ranges. In the upper ionosphere and near-planet magnetotail (h greater than 1800 km), the solar EUV effects are significant. The electron density decreases about an order of magnitude from high to low EUV flux, while the electron temperature at least doubles. The magnetic field also increases 2 - 3 nT. In the lower ionosphere (200 - 600 km), lower EUV fluxes are associated with slightly reduced density, and higher temperature. These results are in accord with recent entry phase observations, where the electron density measured above the ionospheric density peak is lower than that observed at solar maximum during the early Pioneer Venus mission.

Ho, C. M.↗
DOE OSTI2020

Materials Data on Rb3HoO3 by Materials Project

Rb3HoO3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent Rb1+ sites. In the first Rb1+ site, Rb1+ is bonded to four O2- atoms to form distorted RbO4 tetrahedra that share corners with five equivalent HoO4 tetrahedra and an edgeedge with one RbO4 tetrahedra. There are a spread of Rb–O bond distances ranging from 2.85–3.11 Å. In the second Rb1+ site, Rb1+ is bonded in a 3-coordinate geometry to five O2- atoms. There are a spread of Rb–O bond distances ranging from 2.85–3.50 Å. In the third Rb1+ site, Rb1+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Rb–O bond distances ranging from 2.71–3.22 Å. Ho3+ is bonded to four O2- atoms to form HoO4 tetrahedra that share corners with five equivalent RbO4 tetrahedra and an edgeedge with one HoO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.11–2.21 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to six Rb1+ and one Ho3+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to four Rb1+ and two equivalent Ho3+ atoms. In the third O2- site, O2- is bonded in a 5-coordinate geometry to four Rb1+ and one Ho3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Isomeric effects on the reactivity of branched alkenes: An experimental and kinetic modeling study of methylbutenes

Here, a detailed experimental study of the low-to-intermediate temperature combustion of methylbutene isomers, i.e., branched C 5 alkenes, has been undertaken with multiple experimental facilities. Ignition delay times were measured at equivalence ratios 0.5–2.0, 685–1020 K and up to 45 bar condition from two rapid compression machines and showed slight deviation from an Arrhenius behavior for all three isomers, while their reactivity order differs as temperature changes. Sampled intermediates formed during the oxidation process of mixtures at 900–1150 K and 0.82 bar from a flow reactor and at 730 K and 20 bar from a rapid compression machine were analyzed using gas chromatography techniques. Trends in the formation and consumption of sampled intermediates were modeled using a kinetic model developed in this work for all three isomers. Rate of production and sensitivity analyses emphasize the role of double bond-specific reactions governing the global reactivity of these fuels. Additional studies of the addition reactions of HO 2 radicals to the double bond and to allylic radicals may improve the model performance.

2-Methyl-1-butene↗
DOE OSTI2020

Materials Data on HoTa3O9 by Materials Project

HoTa3O9 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ho3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ho–O bond distances ranging from 2.34–2.69 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form TaO6 octahedra that share corners with two equivalent TaO6 octahedra, corners with two equivalent TaO7 pentagonal bipyramids, and edges with two equivalent TaO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 35°. There are a spread of Ta–O bond distances ranging from 1.98–2.01 Å. In the second Ta5+ site, Ta5+ is bonded to seven O2- atoms to form distorted TaO7 pentagonal bipyramids that share a cornercorner with one TaO6 octahedra, corners with two equivalent TaO7 pentagonal bipyramids, an edgeedge with one TaO6 octahedra, and edges with two equivalent TaO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 38°. There are a spread of Ta–O bond distances ranging from 1.94–2.24 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ta5+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+ and two equivalent Ta5+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Ho3+ and two equivalent Ta5+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and two equivalent Ta5+ atoms. In the fifth O2- site, O2- is bonded in a distorted linear geometry to one Ho3+ and two equivalent Ta5+ atoms. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ho3+ and two Ta5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2Si4CN6 by Materials Project

Ho2Si4N6C crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six N3- atoms to form distorted HoN6 pentagonal pyramids that share corners with ten SiCN3 tetrahedra, an edgeedge with one HoN6 pentagonal pyramid, and an edgeedge with one SiCN3 tetrahedra. There are a spread of Ho–N bond distances ranging from 2.33–2.58 Å. In the second Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six N3- atoms. There are a spread of Ho–N bond distances ranging from 2.32–2.87 Å. There are four inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to one C4- and three N3- atoms to form SiCN3 tetrahedra that share corners with two equivalent HoN6 pentagonal pyramids, corners with six SiCN3 tetrahedra, and an edgeedge with one HoN6 pentagonal pyramid. The Si–C bond length is 1.90 Å. There is two shorter (1.75 Å) and one longer (1.77 Å) Si–N bond length. In the second Si4+ site, Si4+ is bonded to one C4- and three N3- atoms to form SiCN3 tetrahedra that share corners with three equivalent HoN6 pentagonal pyramids and corners with six SiCN3 tetrahedra. The Si–C bond length is 1.91 Å. There are a spread of Si–N bond distances ranging from 1.73–1.76 Å. In the third Si4+ site, Si4+ is bonded to one C4- and three N3- atoms to form SiCN3 tetrahedra that share corners with two equivalent HoN6 pentagonal pyramids and corners with six SiCN3 tetrahedra. The Si–C bond length is 1.91 Å. There is one shorter (1.74 Å) and two longer (1.76 Å) Si–N bond length. In the fourth Si4+ site, Si4+ is bonded to one C4- and three N3- atoms to form SiCN3 tetrahedra that share corners with three equivalent HoN6 pentagonal pyramids and corners with six SiCN3 tetrahedra. The Si–C bond length is 1.88 Å. There is two shorter (1.75 Å) and one longer (1.76 Å) Si–N bond length. C4- is bonded to four Si4+ atoms to form CSi4 tetrahedra that share corners with six NHo2Si2 tetrahedra and corners with four NHo2Si2 trigonal pyramids. There are six inequivalent N3- sites. In the first N3- site, N3- is bonded to two Ho3+ and two Si4+ atoms to form distorted NHo2Si2 trigonal pyramids that share corners with two equivalent CSi4 tetrahedra, corners with six NHo2Si2 tetrahedra, a cornercorner with one NHo2Si2 trigonal pyramid, an edgeedge with one NHo2Si2 tetrahedra, and an edgeedge with one NHo2Si2 trigonal pyramid. In the second N3- site, N3- is bonded to two Ho3+ and two Si4+ atoms to form distorted NHo2Si2 trigonal pyramids that share corners with two equivalent CSi4 tetrahedra, corners with six NHo2Si2 tetrahedra, a cornercorner with one NHo2Si2 trigonal pyramid, an edgeedge with one NHo2Si2 tetrahedra, and an edgeedge with one NHo2Si2 trigonal pyramid. In the third N3- site, N3- is bonded to two Ho3+ and two Si4+ atoms to form distorted NHo2Si2 tetrahedra that share corners with two equivalent CSi4 tetrahedra, corners with six NHo2Si2 tetrahedra, corners with three NHo2Si2 trigonal pyramids, and an edgeedge with one NHo2Si2 trigonal pyramid. In the fourth N3- site, N3- is bonded to two equivalent Ho3+ and two Si4+ atoms to form distorted NHo2Si2 tetrahedra that share corners with two equivalent CSi4 tetrahedra, corners with four NHo2Si2 tetrahedra, corners with five NHo2Si2 trigonal pyramids, and an edgeedge with one NHo2Si2 tetrahedra. In the fifth N3- site, N3- is bonded in a 3-coordinate geometry to two Ho3+ and two Si4+ atoms. In the sixth N3- site, N3- is bonded to two equivalent Ho3+ and two Si4+ atoms to form distorted NHo2Si2 tetrahedra that share corners with two equivalent CSi4 tetrahedra, corners with four NHo2Si2 tetrahedra, corners with four NHo2Si2 trigonal pyramids, an edgeedge with one NHo2Si2 tetrahedra, and an edgeedge with one NHo2Si2 trigonal pyramid.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Two VHH Antibodies Neutralize Botulinum Neurotoxin E1 by Blocking Its Membrane Translocation in Host Cells

Botulinum neurotoxin serotype E (BoNT/E) is one of the major causes of human botulism, which is a life-threatening disease caused by flaccid paralysis of muscles. After receptor-mediated toxin internalization into motor neurons, the translocation domain (HN) of BoNT/E transforms into a protein channel upon vesicle acidification in endosomes and delivers its protease domain (LC) across membrane to enter the neuronal cytosol. It is believed that the rapid onset of BoNT/E intoxication compared to other BoNT serotypes is related to its swift internalization and translocation. We recently identified two neutralizing single-domain camelid antibodies (VHHs) against BoNT/E1 termed JLE-E5 and JLE-E9. Here, we report the crystal structures of these two VHHs bound to the LCHN domain of BoNT/E1. The structures reveal that these VHHs recognize two distinct epitopes that are partially overlapping with the putative transmembrane regions on HN, and therefore could physically block membrane association of BoNT/E1. This is confirmed by our in vitro studies, which show that these VHHs inhibit the structural change of BoNT/E1 at acidic pH and interfere with BoNT/E1 association with lipid vesicles. Therefore, these two VHHs neutralize BoNT/E1 by preventing the transmembrane delivery of LC. Furthermore, structure-based sequence analyses show that the 3-dimensional epitopes of these two VHHs are largely conserved across many BoNT/E subtypes, suggesting a broad-spectrum protection against the BoNT/E family. In summary, this work improves our understanding of the membrane translocation mechanism of BoNT/E and paves the way for developing VHHs as diagnostics or therapeutics for the treatment of BoNT/E intoxication.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Materials Data on Ho2Ge2O7 by Materials Project

Ho2Ge2O7 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four 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 2.24–2.41 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 2.23–2.81 Å. In the third 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 2.31–2.62 Å. In the fourth Ho3+ site, Ho3+ is bonded to six O2- atoms to form distorted HoO6 octahedra that share corners with seven GeO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.23–2.40 Å. There are four inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with two equivalent HoO6 octahedra and a cornercorner with one GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–69°. There are a spread of Ge–O bond distances ranging from 1.75–1.80 Å. In the second Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share a cornercorner with one HoO6 octahedra. The corner-sharing octahedral tilt angles are 54°. There are a spread of Ge–O bond distances ranging from 1.74–1.81 Å. In the third Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with three equivalent HoO6 octahedra and corners with two GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 62–68°. There are a spread of Ge–O bond distances ranging from 1.74–1.80 Å. In the fourth Ge4+ site, Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share a cornercorner with one HoO6 octahedra and a cornercorner with one GeO4 tetrahedra. The corner-sharing octahedral tilt angles are 50°. There are a spread of Ge–O bond distances ranging from 1.75–1.88 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to three Ho3+ and one Ge4+ atom to form a mixture of distorted corner and edge-sharing OHo3Ge tetrahedra. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Ho3+ and one Ge4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Ge4+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Ge4+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Ge4+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Ge4+ atom. In the seventh O2- site, O2- is bonded to three Ho3+ and one Ge4+ atom to form distorted corner-sharing OHo3Ge tetrahedra. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Ge4+ atom. In the tenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Ge4+ atom. In the eleventh O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Ge4+ atom. In the twelfth O2- site, O2- is bonded in a 1-coordinate geometry to two Ho3+ and one Ge4+ atom. In the thirteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Ge4+ atom. In the fourteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+ and two Ge4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoSbMo2O9 by Materials Project

HoMo2SbO9 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first 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 2.31–2.45 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 2.33–2.41 Å. There are two inequivalent Mo6+ sites. In the first Mo6+ site, 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. In the second Mo6+ site, Mo6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Mo–O bond distances ranging from 1.77–1.84 Å. Sb3+ is bonded in a distorted rectangular see-saw-like geometry to four O2- atoms. There are a spread of Sb–O bond distances ranging from 2.02–2.30 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to one Ho3+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+ and two equivalent Sb3+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one Mo6+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one Mo6+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Ho3+, one Mo6+, and one Sb3+ atom. In the sixth O2- site, O2- is bonded in a linear geometry to one Ho3+ and one Mo6+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one Mo6+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one Mo6+ atom. In the ninth O2- site, O2- is bonded in a distorted linear geometry to one Mo6+ and one Sb3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optically Induced Picosecond Lattice Compression in the Dielectric Component of a Strongly Coupled Ferroelectric/Dielectric Superlattice

Above-bandgap femtosecond optical excitation of a ferroelectric/dielectric BaTiO 3 /CaTiO 3 superlattice leads to structural responses that are a consequence of the screening of the strong electrostatic coupling between the component layers. Time-resolved X-ray free-electron laser diffraction shows that the structural response to optical excitation includes a net lattice expansion of the superlattice consistent with depolarization-field screening driven by the photoexcited charge carriers. The depolarization-field-screening-driven expansion is separate from a photoacoustic pulse launched from the bottom electrode on which the superlattice is epitaxially grown. The distribution of diffracted intensity of superlattice X-ray reflections indicates that the depolarization-field-screening-induced strain includes a photoinduced expansion in the ferroelectric BaTiO 3 and a contraction in CaTiO 3 . The magnitude of expansion in BaTiO 3 layers is larger than the contraction in CaTiO 3 . The difference in the magnitude of depolarization-field-screening-driven strain in the BaTiO 3 and CaTiO 3 components can arise from the contribution of the oxygen octahedral rotation patterns at the BaTiO 3 /CaTiO 3 interfaces to the polarization of CaTiO 3 . The depolarization-field-screening-driven polarization reduction in the CaTiO 3 layers points to a new direction for the manipulation of polarization in the component layers of a strongly coupled ferroelectric/dielectric superlattice.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Navigation systems requirement analysis for the Aeroassist Flight Experiment (AFE)

Navigation requirements for Aeroassist Flight Experiment (AFE) spacecraft passing through the earth's atmosphere have been studied using a 6-DOF dynamics model, an Inertial Measurement Unit model, a baseline AFE aeropass flight guidance logic, and a baseline AFE aeropass control model. The goal of this study is to determine, in a statistical sense, how much flight path angle error can be tolerated at Entry Interface (EI) and still have acceptable delta-V requirements at exit to position the AFE spacecraft for recovery. Assuming there is fuel available to produce 370 ft/sec of delta-V at atmospheric exit, a 3-sigma standard deviation in flight path angle error of 0.04 degree at EI would result in a 98 percent probability of mission success. In addition to the required delta-V at exit, other aeropass parameters such as maximum aeroheating rate, fuel consumption, and the science requirements affecting mission success are also investigated.

Huang, K. H.↗
DOE OSTI2020

Materials Data on Co3P2(HO)16 by Materials Project

Co3P2(HO)16 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two Co3P2(HO)16 sheets oriented in the (0, 1, 0) direction. there are two inequivalent Co2+ sites. In the first Co2+ site, Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with two equivalent PO4 tetrahedra. There are two shorter (2.08 Å) and four longer (2.16 Å) Co–O bond lengths. In the second Co2+ site, Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with four equivalent PO4 tetrahedra and an edgeedge with one CoO6 octahedra. There are a spread of Co–O bond distances ranging from 2.09–2.19 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with five CoO6 octahedra. The corner-sharing octahedra tilt angles range from 46–57°. There are a spread of P–O bond distances ranging from 1.55–1.58 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.00 Å) and one longer (1.74 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Co2+, one P5+, and two equivalent H1+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Co2+ and one P5+ atom. In the third O2- site, O2- is bonded in a 2-coordinate geometry to one Co2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Co2+ and two H1+ atoms. In the fifth O2- site, O2- is bonded in a distorted water-like geometry to one Co2+ and two H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3P2(HO)16 by Materials Project

Ni3P2(HO)16 crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of two Ni3P2(HO)16 sheets oriented in the (0, 1, 0) direction. there are two inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with two equivalent PO4 tetrahedra. There are two shorter (2.06 Å) and four longer (2.12 Å) Ni–O bond lengths. In the second Ni2+ site, Ni2+ is bonded to six O2- atoms to form NiO6 octahedra that share corners with four equivalent PO4 tetrahedra and an edgeedge with one NiO6 octahedra. There are a spread of Ni–O bond distances ranging from 2.06–2.15 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with five NiO6 octahedra. The corner-sharing octahedra tilt angles range from 46–58°. There are a spread of P–O bond distances ranging from 1.55–1.58 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.01 Å) and one longer (1.70 Å) H–O bond length. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to one Ni2+, one P5+, and two equivalent H1+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ni2+ and one P5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to one Ni2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Ni2+ and two H1+ atoms. In the fifth O2- site, O2- is bonded in a distorted water-like geometry to one Ni2+ and two H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interfacial stabilization for epitaxial CuCrO 2 delafossites

AB O 2 delafossites are fascinating materials that exhibit a wide range of physical properties, including giant Rashba spin splitting and anomalous Hall effects, because of their characteristic layered structures composed of noble metal A and strongly correlated B O 2 sublayers. However, thin film synthesis is known to be extremely challenging owing to their low symmetry rhombohedral structures, which limit the selection of substrates for thin film epitaxy. Hexagonal lattices, such as those provided by Al 2 O 3 (0001) and (111) oriented cubic perovskites, are promising candidates for epitaxy of delafossites. However, the formation of twin domains and impurity phases is hard to suppress, and the nucleation and growth mechanisms thereon have not been studied for the growth of epitaxial delafossites. In this study, we report the epitaxial stabilization of a new interfacial phase formed during pulsed-laser epitaxy of (0001)-oriented CuCrO 2 epitaxial thin films on Al 2 O 3 substrates. Through a combined study using scanning transmission electron microscopy/electron-energy loss spectroscopy and density functional theory calculations, we report that the nucleation of a thermodynamically stable, atomically thick CuCr 1-x Al x O 2 interfacial layer is the critical element for the epitaxy of CuCrO 2 delafossites on Al 2 O 3 substrates. This finding provides key insights into the thermodynamic mechanism for the nucleation of intermixing-induced buffer layers that can be used for the growth of other noble-metal-based delafossites, which are known to be challenging due to the difficulty in initial nucleation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Accelerating the discovery of novel magnetic materials using machine learning–guided adaptive feedback

Magnetic materials are essential for energy generation and information devices, and they play an important role in advanced technologies and green energy economies. Currently, the most widely used magnets contain rare earth (RE) elements. An outstanding challenge of notable scientific interest is the discovery and synthesis of novel magnetic materials without RE elements that meet the performance and cost goals for advanced electromagnetic devices. Here, we report our discovery and synthesis of an RE-free magnetic compound, Fe 3 CoB 2 , through an efficient feedback framework by integrating machine learning (ML), an adaptive genetic algorithm, first-principles calculations, and experimental synthesis. Magnetic measurements show that Fe 3 CoB 2 exhibits a high magnetic anisotropy ( K 1 = 1.2 MJ/m 3 ) and saturation magnetic polarization ( J s = 1.39 T), which is suitable for RE-free permanent-magnet applications. Our ML-guided approach presents a promising paradigm for efficient materials design and discovery and can also be applied to the search for other functional materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Searching for correlations between vibrational spectral features and structural parameters of silicate glass network

Infrared (IR) and Raman spectroscopic features of silicate glasses are usually interpreted based on the analogy with those of smaller molecules, molecular clusters, or crystalline counterparts; this study tests the accuracy and validity of these widely cited peak assignment schemes by comparing vibrational spectral features with bond parameters of the glass network created by molecular dynamics (MD) simulations. A series of sodium silicate glasses with compositions of [Na 2 O] x [Al 2 O 3 ] 2 [SiO 2 ] 98- x with x = 7, 12, 17, and 22 were synthesized and analyzed with IR and Raman. A silica glass substrate and a crystalline quartz were also analyzed for comparison. Glass structures with the same compositions were generated with MD simulations using three types of potentials: fixed partial charge pairwise (Teter), partial diffuse charge potential (MGFF), and bond order-based charge transfer potential (ReaxFF). The comparison of simulated and experimental IR spectra showed that, among these three potentials tested, ReaxFF reproduces the concentration dependence of spectral features closest to the experimentally observed trend. Hence, the bond length and angle distributions as well as Si– Q n species and ring size distributions of silica and sodium silicate glasses were obtained from ReaxFF-MD simulations and further compared with the peak assignment or deconvolution schemes—which have been widely used since 1970s and 1980s—(a) correlation between the IR peak position in the Si–O stretch region (1050-1120 cm -1 ) and the Si–O–Si bond angle; (b) deconvolution of the Raman bands in the Si–O stretch region with the Q n speciation; and (c) assignment of the Raman bands in the 420-600 cm -1 region to the bending modes of (SiO) n rings with different sizes (typically, n = 3-6). The comparisons showed that none of these widely used methods is congruent with the bond parameters or structures of silicate glass networks produced via ReaxFF-MD simulations. This result invokes that the adequacy of these spectral interpretation methods must be questioned. Alternative interpretations are proposed, which are to be tested independently in future studies.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Quantum Molecular Charge-Transfer Model for Multistep Auger–Meitner Decay Cascade Dynamics

The fragmentation of molecular cations following inner-shell decay processes in molecules containing heavy elements underpins the X-ray damage effects observed in X-ray scattering measurements of biological and chemical materials, as well as in medical applications involving Auger electron-emitting radionuclides. Traditionally, these processes are modeled using simulations that describe the electronic structure at an atomic level, thereby omitting molecular bonding effects. This work addresses the gap by introducing a novel approach that couples Auger–Meitner decay to nuclear dynamics across multiple decay steps, by developing a decay spawning dynamics algorithm and applying it to potential energy surfaces characterized with ab initio molecular dynamics simulations. We showcase the approach on a model decay cascade following K-shell ionization of IBr and subsequent Kβ fluorescence decay. We examine two competing channels that undergo two decay steps, resulting in ion pairs with a total 3+ charge state. This approach provides a continuous description of the electron transfer dynamics occurring during the multistep decay cascade and molecular fragmentation, revealing the combined inner-shell decay and charge transfer time scale to be approximately 75 fs. In conclusion, our computed kinetic energies of ion fragments show good agreement with experimental data.

Ab initio molecular dynamics↗
NASA NTRS1995

The middle atmospheric response to short and long term solar UV variations: analysis of observations and 2D model results

We have investigated the middle atmospheric response to the 27-day and 11-yr solar UV flux variations at low to middle latitudes using a two-dimensional photochemical model. The model reproduced most features of the observed 27-day sensitivity and phase lag of the profile ozone response in the upper stratosphere and lower mesosphere, with a maximum sensitivity of +0.51% per 1% change in 205 nm flux. The model also reproduced the observed transition to a negative phase lag above 2 mb, reflecting the increasing importance with height of the solar modulated HO(x) chemistry on the ozone response above 45 km. The model revealed the general anti-correlation of ozone and solar UV at 65-75 km, and simulated strong UV responses of water vapor and HO(x) species in the mesosphere. Consistent with previous 1D model studies, the observed upper mesospheric positive ozone response averaged over +/- 40 was simulated only when the model water vapor concentrations above 75 km were significantly reduced relative to current observations. In agreement with observations, the model computed a low to middle latitude total ozone phase lag of +3 days and a sensitivity of +0.077% per 1% change in 205 nm flux for the 27-day solar variation, and a total ozone sensitivity of +0.27% for the 11-yr solar cycle. This factor of 3 sensitivity difference is indicative of the photochemical time constant for ozone in the lower stratosphere which is comparable to the 27-day solar rotation period but is much shorter than the 11-yr solar cycle.

Fleming, Eric L.↗