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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.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Striking stability of a mixed-valence thallium(III)-thallium(I) complex in some solvents

At the dissolution of solid anhydrous thallium(III) trifluoromethanesulfonate, Tl(CF 3 SO 3 ) 3 , or thallium(III) trifluoroacetate, Tl(CF 3 COO) 3 , in dimethylsulfoxide (dmso) or N,N,N’,N’-tetramethylurea (tmu), intensely red-colored complexes are formed. This red thallium complex is stable for years in dmso, while it is reduced fairly rapidly to thallium(I) in tmu with a half-life time of an hour. At the dissolution of Tl(CF 3 SO 3 ) 3 in N,N-dimethylpropyleneurea (dmpu) an immediate reduction to thallium(I) takes place. A stable colorless aqueous thallium(III) solution is obtained at the dissolution in acidic water. Stable dmso solutions and solid dmso solvates of thallium(III) perchlorate, nitrate and trifluormethanesulfonate can be prepared by adding dmso to concentrated acidic aqueous thallium(III) solutions. These experimental observations conclude that the pure solids Tl(CF 3 SO 3 ) 3 and Tl(CF 3 COO) 3 play an essential role in the formation of the red-colored thallium complexes. 205 Tl NMR data show that the red thallium complex contains equal amounts of thallium(III) and thallium(I). The structure of the red thallium complex in dmso, as determined by EXAFS, has Tl–O bond distances of 2.216(3) and 2.80(2) Å, which are in very close agreement with the bond distances obtained in the pure dmso solvates of the thallium(III) and thallium(I) ions, respectively, and a Tl···Tl distance of 3.49(1) Å bridged by oxygen atoms. From the EXAFS data it is impossible to distinguish if dmso molecules and/or trifluoromethanesulfonate ions act as bridges. DFT calculations could eliminate some structures due to the irrelevant structural parameters or the energetics of the proposed reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Degeneracy and effective mass in the valence band of two-dimensional (100)-GaAs quantum well systems

Quantum Hall measurement of two-dimensional high-mobility [μ∼2×10{sup 6} cm{sup 2}/(V·s)] hole systems confined in a 20 nm wide (100)-GaAs quantum well have been performed for charge densities between 4 and 5 × 10{sup 10} cm{sup −2} in a temperature range of 10–160 mK. The Fourier analysis of the Shubnikov-de Haas (SdH) oscillations of the magnetoresistance vs. the inverse of the magnetic field 1/B reveals a single peak, indicating a degenerate heavy hole (HH) band. The hole density p=(e/h)·f agrees with the Hall measurement result within 3%. The HH band degeneracy is understood through the diminishing spin-orbit interaction due to the low charge density and the nearly symmetric confinement. SdH oscillations fitted for 0.08 T ≤ B ≤ 0.24 T to the Dingle parameters yield an effective mass between 0.30 and 0.50 m{sub e} in good agreement with previous cyclotron resonance results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Synchrotron-based valence shell photoionization of CH radical

We report the first experimental observations of X{sup +} {sup 1}Σ{sup +}←X {sup 2}Π and a{sup +} {sup 3}Π←X {sup 2}Π single-photon ionization transitions of the CH radical performed on the DESIRS beamline at the SOLEIL synchrotron facility. The radical was produced by successive hydrogen-atom abstractions on methane by fluorine atoms in a continuous microwave discharge flow tube. Mass-selected ion yields and photoelectron spectra were recorded as a function of photon energy using a double imaging photoelectron/photoion coincidence spectrometer. The ion yield appears to be strongly affected by vibrational and electronic autoionizations, which allow the observation of high Rydberg states of the neutral species. The photoelectron spectra enable the first direct determinations of the adiabatic ionization potential and the energy of the first triplet state of the cation with respect to its singlet ground state. This work also brings valuable information on the complex electronic structure of the CH radical and its cation and adds new observations to complement our understanding of Rydberg states and autoionization processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Bandgap profiling in CIGS solar cells via valence electron energy-loss spectroscopy

A robust, reproducible method for the extraction of relative bandgap trends from scanning transmission electron microscopy (STEM) based electron energy-loss spectroscopy (EELS) is described. The effectiveness of the approach is demonstrated by profiling the bandgap through a CuIn 1-x Ga x Se 2 solar cell that possesses intentional Ga/(In + Ga) composition variation. The EELS-determined bandgap profile is compared to the nominal profile calculated from compositional data collected via STEM-based energy dispersive X-ray spectroscopy. The EELS based profile is found to closely track the calculated bandgap trends, with only a small, fixed offset difference. This approach, which is particularly advantageous for relatively narrow bandgap materials and/or STEM systems with modest resolution capabilities (i.e., >100 meV), compromises absolute accuracy to provide a straightforward route for the correlation of local electronic structure trends with nanoscale chemical and physical structure/microstructure within semiconductor materials and devices.

14 SOLAR ENERGY↗
DOE OSTI2016

Ellipticity dependence of high harmonic yield in intense laser field: case of s-valence electron

Having solved numerically the time-dependent Schrödinger equation, we have analysed the dependence of the high harmonic generation yield on the ellipticity of an intense laser field. For the case of a zero angular momentum of an initial state, it has been shown that the ellipticity dependence of the HHG yield is affected by the harmonic number. The numerical results are interpreted in the framework of our recently developed quasi-classical analytical model for HHG. In the quasi-classical approximation, the difference in the ellipticity dependence of the HHG yield for different harmonics is shown to be caused by the interference effects of quantum orbits. (extreme laser radiation: physics and fundamental applications)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Complexation and Solvent Extraction Studies of High Valency Actinides by Hard/Soft Donor Schiff Base Ligands

Successful separation of the mid actinides (U, Np, Pu, Am) from other elements is imperative for drastically lowering the long term radiotoxicity of SNF. Ubiquitous to these mid actinides is a wide range of oxidation states (+III, +IV, +V, +VI) where the +V and +VI oxidation states exist in a linear dioxo actinyl cation AnO{sub 2}{sup n+} (O=An=O){sup n+} guaranteeing unique ligand coordination about the equatorial plane. Multidentate Schiff base ligands which possess nitrogen and oxygen donor groups can accommodate the steric demands of the actinyl cations as well as providing selectivity for actinides in a separation process. Group extraction or retention of the mid actinides in a biphasic solvent extraction process can be achieved by complexation of their actinyl species by Schiff base ligands in one phase while all other non actinyl cations are complexed in the other phase. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Identifying Dense NiSe 2 /CoSe 2 Heterointerfaces Coupled with Surface High-Valence Bimetallic Sites for Synergistically Enhanced Oxygen Electrocatalysis

Constructing heterostructures with abundant interfaces is essential for integrating the multiple functionalities in single entities. Herein, the synthesis of NiSe 2 /CoSe 2 heterostructures with different interfacial densities via an innovative strategy of successive ion injection is reported. The resulting hybrid electrocatalyst with dense heterointerfaces exhibits superior electrocatalytic properties in an alkaline electrolyte, superior to other benchmarks and precious metal catalysts. Advanced synchrotron techniques, post structural characterizations, and density functional theory (DFT) simulations reveal that the introduction of atomic-level interfaces can lower the oxidation overpotential of bimetallic Ni and Co active sites (whereas Ni$^{2+}$ can be more easily activated than Co$^{2+}$) and induce the electronic interaction between the core selenides and surface in situ generated oxides/hydroxides, which play a critical role in synergistically reducing energetic barriers and accelerating reaction kinetics for catalyzing the oxygen evolution. Hence, the heterointerface structure facilitates the catalytic performance enhancement via increasing the intrinsic reactivity of metallic atoms and enhancing the synergistic effect between the inner selenides and surface oxidation species. This work not only complements the understanding on the origins of the activity of electrocatalysts based on metal selenides, but also sheds light on further surface and interfacial engineering of advanced hybrid materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Deactivation of a Cobalt Catalyst for Water Reduction through Valence Tautomerism

The activity of the water reduction catalyst [Co III (L 1 )(pyr) 2 ]PF 6 (1), where (L 1 ) 2- is a bis-amido pyridine ligand and pyr is pyrrolidine, is investigated. Catalyst 1 has an overpotential of 0.54 V and a high observed TOF of 23 min -1 , albeit for a relatively short time. Considering the significant activity of 1 and aiming to improve catalyst design, a detailed structural and electronic study is performed to understand the mechanisms of deactivation. Experimental and theoretical evidence support that the metal-reduced [Co I (L 1 )] - is in tautomeric equilibrium with the ligand-reduced [Co II (L 1 .)] - species. While [Co I (L 1 )] - favors formation of a Co III -H - relevant for catalysis, the [Co II (L 1 .)] - species leads to ligand protonation, structural distortions, and, ultimatley, catalyst deactivation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Magnetic Studies on New Mixed-Valence Phosphates Zn{sup 2+}Fe{sub 2}{sup 3+}(P{sub 2}O{sub 7}){sub 2} and Zn{sub 0.5}{sup 2+}Cu{sub 0.5}{sup 2+}Fe{sub 2}{sup 3+}(P{sub 2}O{sub 7}){sub 2}

Structural studies of Zn{sup 2+}Fe{sub 2}{sup 3+}(P{sub 2}O{sub 7}){sub 2} and Cu{sub 0.5}Zn{sub 0.5}Fe{sub 2}(P{sub 2}O{sub 7}){sub 2} were made using powder X-ray diffraction and refined by Rietveld method. Both phosphates crystallize in an orthorhombic structure with Pnma space group. Magnetometry measurements showed that below T{sub N} = 5.6 (1), Zn{sup 2+}Fe{sub 2}{sup 3+}(P{sub 2}O{sub 7}){sub 2} becomes antiferromagnetic and the T{sub N} = 14 K is attributed to Cu{sub 0.5}Zn{sub 0.5}Fe{sub 2}(P{sub 2}O{sub 7}){sub 2}. Mössbauer studies at room temperature and low temperature were performed in both samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗