Gamma single-hit detector for NDSE, LAO-034-21, Year 1 of 3
Presentation to be presented during the Site-Directed Research and Development (SDRD) program FY 2021 review meeting (Webex), September 22–23, 2021.
Schwellenbach, David↗
SEARCH · Engineering Papers
Results for “LaO”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Detector Wall Research for Fast Gamma Signal Detection in Neutron-Diagnosed Subcritical Experiment Applications Project #: LAO-026-20 Year 3 of 3
Explore the source record for details and available documents.
Baker, Stuart A↗
Measurement of Dynamic Melting and Re-Crystallization of Shocked Metals Project #: LAO-031-21 Year 2 of 3
Explore the source record for details and available documents.
36 MATERIALS SCIENCE↗
Achieving Multimodal and Multicolor Luminescence in LaAlO 3 :Pr 3+ , Gd 3+ via Trap Engineering and Energy Transfer
Achieving multimodal luminescence within a single phosphor is vital for multifunctional applications but remains challenging due to complex color tuning and trap engineering. In this study, we report Pr 3+ and Gd 3+ co‐doped LaAlO 3 (LAO:PG) phosphors, designed through careful modulation of multilevel traps and Pr 3+ → Gd 3+ energy transfer dynamics. These materials exhibit diverse luminescence modes, including down‐conversion luminescence (DCL), up‐conversion luminescence (UCL), persistent luminescence (PersL), optically stimulated luminescence (OSL), and thermally stimulated luminescence (TSL) across a wide spectral range. Unlike previously studied Pr 3+ ‐doped LAO, the co‐doped LAO:PG shows DCL in both UV‐visible and NIR regions and displays ultraviolet‐C UCL under visible excitation. Notably, we observe, for the first time, PersL lasting several minutes in these phosphors—an improvement over the non‐PersL behavior of Pr 3+ ‐only doped LAO. Additionally, the LAO:PG phosphors exhibit strong OSL response. TSL analysis reveals five distinct trap levels linked to these properties. Density functional theory calculations further correlate intrinsic defects to these traps, supporting a proposed mechanism for the observed multimodal luminescence. These findings highlight LAO:PG as a promising platform for developing advanced phosphors with integrated luminescence modes, paving the way for future applications in data storage, phototherapy, and anti‐counterfeiting technologies.
Chemistry↗
Energetic and Electronic Properties of AcX and LaX (X = O and F)
The bonding and spectroscopic properties of LaX and AcX (X = O and F) diatomic molecules were studied by highlevel ab initio CCSD(T) and SO-CASPT2 electronic structure calculations. Bond dissociation energies (BDEs) were calculated at the Feller−Peterson−Dixon (FPD) level. Potential energy curves and spectroscopic constants for the lowest-lying spin−orbit Ω states were obtained at the SO-CASPT2/aQ-DK level. A dense manifold of excited states was described for the monofluorides with the ground states well separated from the excited states. The spectroscopic parameters were in good agreement with those reported experimentally for LaO and LaF. For the diatomic molecules containing actinides, no experimental data of these parameters was found, but the results were consistent with other high-level calculations. The BDEs calculated at the FPD level were 791.3 (LaO), 705.2 (AcO), 650.0 (LaF), and 678.6 (AcF) kJ/ mol. The NBO analysis showed that the monofluorides are essentially ionic, which explains why the BDE(AcF) is higher than BDE(LaF); for the monoxides, covalent contributions involving the d orbitals of the metal and the p orbitals of the oxygen are stronger for LaO than AcO, which explains the higher BDE for LaO. Finally, the bond orders are predicted to be 2 for LaF and AcF, 3 for AcO, and higher than 3 for LaO.
Basis sets↗
Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2
Abstract Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives 1–3 . Their conversion first generates syngas, a mixture of CO and H 2 , which is then processed further using Fischer–Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present 4–8 . The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO 2 waste that leads to a low carbon utilization efficiency 9–14 . The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C 5 –C 10 LAOs than are found in the C 2 –C 4 olefins that dominate the product mixtures 9–14 . Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1–2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. 12–15 ), is stable for 200 h, and produces desired C 2 –C 10 LAOs and unwanted CO 2 with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250–320 °C), demonstrates the potential of the system for developing a practically relevant technology.
Science & Technology - Other Topics↗
GONG Catalog of Solar Filament Oscillations Near Solar Maximum
We have cataloged 196 filament oscillations from the Global Oscillation Network Group Hα network data during several months near the maximum of solar cycle 24 (2014 January–June). Selected examples from the catalog are described in detail, along with our statistical analyses of all events. Oscillations were classified according to their velocity amplitude: 106 small-amplitude oscillations (SAOs), with velocities <10 km s-1, and 90 large-amplitude oscillations (LAOs), with velocities >10 km s-1. Both SAOs and LAOs are common, with one event of each class every two days on the visible side of the Sun. For nearly half of the events, we identified their apparent trigger. The period distribution has a mean value of 58 ± 15 minutes for both types of oscillations. The distribution of the damping time per period peaks at τ/P = 1.75 and 1.25 for SAOs and LAOs, respectively. We confirmed that LAO damping rates depend nonlinearly on the oscillation velocity. The angle between the direction of motion and the filament spine has a distribution centered at 27° for all filament types. This angle agrees with the observed direction of filament-channel magnetic fields, indicating that most of the cataloged events are longitudinal (i.e., undergo field-aligned motions). We applied seismology to determine the average radius of curvature in the magnetic dips, R ≈ 89 Mm, and the average minimum magnetic field strength, B ≈ 16 G. The catalog is available to the community online and is intended to be expanded to cover at least 1 solar cycle.
Filaments↗
Understanding the Origin of Negative Temperature Dependence and Activity of N-Coordinated Cobalt Sites During Ethylene Dimerization
The on-demand production of short-chain linear alpha olefins (LAOs; C4-C8) via C2H4 dimerization and oligomerization is industrially attractive, prompting extensive research on designing active, selective, and stable catalysts for industrial use. Cobalt supported on ammoniated carbon (Co(NH3)x/C) catalysts have shown remarkable activity and selectivity in this process. However, critical aspects such as the active phase, active site structure, the role of the catalyst support, cobalt loading effects, and the inverse correlation of the reaction rate with temperature remain inadequately understood. This study systematically explores these factors using a combination of steady-state differential catalytic tests, in situ molecular characterization including diffuse reflectance UV-Vis (DR-UV-Vis), Infrared, and Raman spectroscopies, and ex situ X-ray diffraction (XRD) and high annular aberration-corrected dark field transmission electron microscopy (HAADF-STEM). Various supports (SiO2, Al2O3, NH4-ZSM-5, g-C3N4, and C) and cobalt loadings (1.0-3.0 Co nm-2) were studied to determine the optimal catalyst composition and identify the active phase and sites. Carbon-supported catalysts uniquely produce C4-8 LAOs during C2H4 dimerization, with site-time-yield remaining constant (~10-3 s-1) for 1.0-4.0 Co nm-2 at prolonged reaction times (24-48?h time-on-stream). At higher loadings of 6.0 Co nm-2, the formation of crystalline CoO and Co3O4 phases reduces catalytic activity and LAO selectivity. Our findings show that active catalysts lack crystalline cobalt oxides and instead feature dispersed Co2+ sites, tetra-coordinated to a mix of N/NH3 and O/H2O ligands, which catalyze C2H4 dimerization via the Cossee-Arlman mechanism, exhibiting 1st order dependence on C2H4 concentration. The observed inverse rate-temperature correlation is attributed to compensation effects (i.e., presence of Cremer-Constable relationship) linked to changes in adsorption enthalpic and entropic factors.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
In situ investigation of conducting interface formation in $\mathrm{LaAlO_3}$/$\mathrm{SrTiO_3}$ heterostructure
The high-mobility conducting interface (CI) between LaAlO 3 (LAO) and SrTiO 3 (STO) has revealed many fascinating phenomena, including exotic magnetism and superconductivity. But, the formation mechanism of the CI has not been conclusively explained. Here, using in situ angle-resolved photoemission spectroscopy, we elucidated the mechanisms for the CI formation. In as-grown samples, we observed a built-in potential (V bi ) proportional to the polar LAO thickness starting from the first unit cell (UC) with CI formation appearing above 3 UCs. However, we found that the V bi is removed by synchrotron ultraviolet (UV)-irradiation; The built-in potential is recovered by oxygen gas (O 2 (g))-exposure. Furthermore, after UV-irradiation, the CI appears even below 3UC of LAO. Here, our results demonstrate not only the V bi -driven CI formation in as-grown LAO/STO, but also a new route to control of the interface state by UV lithographic patterning or other surface modification.
36 MATERIALS SCIENCE↗
Threshold Ionization Spectroscopy and Theoretical Calculations of LnO (Ln = La and Ce)
Mass-analyzed threshold ionization (MATI) spectroscopy was used to measure the vibronic spectra of LnO (Ln = La and Ce). Single-reference coupled cluster and relativistic multireference configuration calculations were carried out to compare with the measured vibronic energies. The spectrum of LaO displays a single vibronic band system, while that of CeO shows multiple ones. The ionization energies of LaO and CeO are measured as 5.2446 (6) and 5.3332(6) eV, respectively, which are a hundredfold improvement over the literature values. The vibrational energies of the neutral molecule and corresponding ion reveal the charge effect on the metal-oxygen bond of both species. The single band system in the spectrum of LaO arises from the transition of the ground state of the neutral molecule with the La(6s 1 )O(2p 6 ) valence configuration to the ground state of the singly charged ion with the La(6s o )O(2p 6 ) configuration. Here, the multiple band systems in the spectrum of CeO are attributed to the spin-orbit coupling for the Ce(4f 1 6s 1 )O(2p 6 ) configuration of the neutral molecule and an excited state for the Ce(4f 1 )O(2p 6 ) configuration of the ion.
74 ATOMIC AND MOLECULAR PHYSICS↗
Renewable linear alpha-olefins by base-catalyzed dehydration of biologically-derived fatty alcohols
In this work, base catalysts were studied for the dehydration of fatty alcohols to linear alpha olefins (LAOs). For the dehydration of 1-octanol to 1-octene, 15%Cs/SiO 2 catalyst was 56% selective at 10% conversion. Diluting a feed of C 8 , C 10 , and C 14 fatty alcohols to 50% in undecane increased the selectivity to alpha olefins to 77-99%. 15%Cs/SiO 2 was further investigated for the dehydration of a 4.2 g/L mixed C 8 -C 14 fatty alcohol in tridecane feed and showed linear alpha olefin selectivities of 78-100% at initial conversions of 51-91% with the conversion lowering to 32-77% over 30 h. Catalytic activity was totally regenerated through calcination. A feed of biologically derived alcohols was produced with E. coli strain CM24 transformed with three plasmids (pBTRCk – pVHb – maACR, pACYC – pVHb – seFadBA, pTRC99A – pVHb – tdTER – fdh) which yielded a 5.5 g/L of C 8 -C 14 fatty alcohol in tridecane. This biologically-derived feed was successfully dehydrated to linear alpha olefins over 15%Cs/SiO 2 at selectivities of 60-100% with initial conversions of 35-75% which decreased to 22-55% over 30 h. Techno-economic analysis (TEA) of the integrated process for fatty alcohol production and subsequent dehydration to alpha olefins was conducted across the potential fermentation TRY (titer, rate, yield) landscape. Baseline fermentation performance resulted in a minimum product selling price (MPSP) double the market price for LAOs due to low titers and high costs associated with managing water and tridecane solvent flows through the system. However, targeted improvements in fermentation performance (e.g., achieving 40 g/L titer, 0.5 g/L/h productivity, 80% theoretical yield) can enable financially viable production of biologically derived LAOs.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
First-principles modeling of conductivity at the (001), (110), and (111) SrTiO 3 /LaAlO 3 heterointerfaces
Here, the complex polar oxide heterojunction of SrTiO 3 /LaAlO 3 (STO/LAO) is of great interest due to the emergent physical phenomena observed at the interface. STO and LAO separately are wide band-gap insulators. However, upon joining them at the 001, 110, and 111 crystallographic planes, the interface undergoes a transition to a conductive state. Although first-principles modeling of the 001 plane interface has been widely studied, there is a lack of reports regarding the 110 and 111. This paper expands the theoretical model of the STO/LAO heterointerface to the three crystallographic planes (001, 110, and 111) where the conductivity has been experimentally reported. The calculations showed that whereas at the 001 interface the conductivity appears at a critical thickness of 4 monolayers of LAO, the 110 and 111 planes have no clear critical thickness; these two interfaces were always conductive. Nevertheless, the number of conductive electrons per unit cell increases with the thickness of the LAO layer in the 110 and 111 interfaces. This is related to the energy levels downshifting due to the electrostatic potential buildup (which was in the opposite direction respect to the 001 interface), increasing the number of conductive sates below the Fermi level. Given the absence of a critical thickness and the fact that chemical intermixing and oxygen vacancies at the interface were not considered, the main mechanism responsible for the conductivity in the 110 and 111 planes was attributed to the large structure reconstruction that locally changes the energy levels at the interface causing charge transfer and accumulation at the layers close to the interface.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Data for Renewable Linear Alpha-Olefins by Base-Catalyzed Dehydration of Biologically-Derived Fatty Alcohols
Base catalysts were studied for the dehydration of fatty alcohols to linear alpha olefins (LAOs). For the gas phase dehydration of 1-octanol to 1-octene, 15% Cs/SiO2 catalyst was 56% selective at 10% conversion. Diluting a feed of C8, C10, and C14 fatty alcohols to 50% in undecane increased the selectivity to alpha olefins to 77–99%. 15% Cs/SiO2 was further investigated for the gas phase dehydration of a 4.2 g L−1 mixed C8–C14 fatty alcohol in tridecane feed and showed linear alpha olefin selectivities of 78–100% at initial conversions of 51–91% with the conversion lowering to 32–77% over 30 h. Catalytic activity was totally regenerated through calcination. A feed of biologically derived alcohols was produced with E. coli strain CM24 transformed with three plasmids (pBTRCk–pVHb–maACR, pACYC–pVHb–seFadBA, pTRC99A–pVHb–tdTER–fdh) which yielded a 5.5 g L−1 of C8–C14 fatty alcohol in tridecane. This biologically-derived feed was successfully dehydrated to linear alpha olefins over 15% Cs/SiO2 at selectivities of 60–100% with initial conversions of 35–75% which decreased to 22–55% over 30 h. Techno-economic analysis (TEA) of the integrated process for fatty alcohol production and subsequent dehydration to alpha olefins was conducted across the potential fermentation TRY (titer, rate, yield) landscape. Baseline fermentation performance resulted in a minimum product selling price (MPSP) double the market price for LAOs due to low titers and high costs associated with managing water and tridecane solvent flows through the system. However, targeted improvements in fermentation performance (e.g., achieving 40 g L−1 titer, 0.5 g L−1 h−1 productivity, 80% theoretical yield) can enable financially viable production of biologically derived LAOs.
Catalysis↗
Materials Data on LaGaSe2O by Materials Project
(LaO)GaSe2 crystallizes in the orthorhombic Pca2_1 space group. The structure is two-dimensional and consists of one GaSe2 sheet oriented in the (0, 0, 1) direction and one LaO sheet oriented in the (0, 0, 1) direction. In the GaSe2 sheet, Ga3+ is bonded to four Se2- atoms to form corner-sharing GaSe4 tetrahedra. There are one shorter (2.35 Å) and three longer (2.47 Å) Ga–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted single-bond geometry to one Ga3+ atom. In the second Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to three equivalent Ga3+ atoms. In the LaO sheet, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are a spread of La–O bond distances ranging from 2.41–2.44 Å. O2- is bonded to four equivalent La3+ atoms to form a mixture of distorted corner and edge-sharing OLa4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on La2SnS3O2 by Materials Project
(LaO)2SnS3 crystallizes in the orthorhombic Pnma space group. The structure is two-dimensional and consists of two SnS3 ribbons oriented in the (0, 1, 0) direction and two LaO sheets oriented in the (0, 0, 1) direction. In each SnS3 ribbon, Sn4+ is bonded to four S2- atoms to form corner-sharing SnS4 tetrahedra. There are a spread of Sn–S bond distances ranging from 2.38–2.49 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in an L-shaped geometry to two equivalent Sn4+ atoms. In the second S2- site, S2- is bonded in a 1-coordinate geometry to one Sn4+ atom. In each LaO sheet, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. There are three shorter (2.41 Å) and one longer (2.42 Å) La–O bond lengths. O2- is bonded to four equivalent La3+ atoms to form a mixture of distorted edge and corner-sharing OLa4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on LaCuSO by Materials Project
(LaO)CuS is Parent of FeAs superconductors structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one CuS sheet oriented in the (0, 0, 1) direction and one LaO sheet oriented in the (0, 0, 1) direction. In the CuS sheet, Cu1+ is bonded to four equivalent S2- atoms to form a mixture of corner and edge-sharing CuS4 tetrahedra. All Cu–S bond lengths are 2.42 Å. S2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms. In the LaO sheet, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All La–O bond lengths are 2.36 Å. O2- is bonded to four equivalent La3+ atoms to form a mixture of corner and edge-sharing OLa4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on La3Cu4(P2O)2 by Materials Project
La(CuP)4(LaO)2 crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two La(CuP)4 sheets oriented in the (0, 0, 1) direction and two LaO sheets oriented in the (0, 0, 1) direction. In each La(CuP)4 sheet, La3+ is bonded to eight equivalent P3- atoms to form LaP8 hexagonal bipyramids that share corners with sixteen equivalent CuP4 tetrahedra, edges with four equivalent LaP8 hexagonal bipyramids, edges with eight equivalent CuP4 tetrahedra, and faces with four equivalent LaP8 hexagonal bipyramids. All La–P bond lengths are 3.08 Å. Cu+1.75+ is bonded to four P3- atoms to form CuP4 tetrahedra that share corners with four equivalent LaP8 hexagonal bipyramids, corners with four equivalent CuP4 tetrahedra, edges with two equivalent LaP8 hexagonal bipyramids, and edges with four equivalent CuP4 tetrahedra. There are two shorter (2.35 Å) and two longer (2.47 Å) Cu–P bond lengths. There are two inequivalent P3- sites. In the first P3- site, P3- is bonded in a 9-coordinate geometry to four equivalent La3+, four equivalent Cu+1.75+, and one P3- atom. The P–P bond length is 2.26 Å. In the second P3- site, P3- is bonded in a 4-coordinate geometry to four equivalent Cu+1.75+ atoms. In each LaO sheet, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All La–O bond lengths are 2.37 Å. O2- is bonded to four equivalent La3+ atoms to form a mixture of edge and corner-sharing OLa4 tetrahedra.
36 MATERIALS SCIENCE↗
Materials Data on La4Cu4Se3SO4 by Materials Project
(LaO)4Cu4Se3S crystallizes in the tetragonal P4mm space group. The structure is two-dimensional and consists of one Cu4Se3S sheet oriented in the (0, 0, 1) direction and one LaO sheet oriented in the (0, 0, 1) direction. In the Cu4Se3S sheet, Cu1+ is bonded to three Se2- and one S2- atom to form a mixture of edge and corner-sharing CuSe3S tetrahedra. There are one shorter (2.52 Å) and two longer (2.53 Å) Cu–Se bond lengths. The Cu–S bond length is 2.42 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms. S2- is bonded in a 4-coordinate geometry to four equivalent Cu1+ atoms. In the LaO sheet, there are three inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All La–O bond lengths are 2.38 Å. In the second La3+ site, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All La–O bond lengths are 2.39 Å. In the third La3+ site, La3+ is bonded in a 4-coordinate geometry to four equivalent O2- atoms. All La–O bond lengths are 2.38 Å. O2- is bonded to four La3+ atoms to form a mixture of edge and corner-sharing OLa4 tetrahedra.
36 MATERIALS SCIENCE↗