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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Synthesis, crystal growth, structural and magnetic characterization of NH{sub 4}MCl{sub 2}(HCOO), M=(Fe, Co, Ni)

An ambient-pressure solution route and an improved solvothermal synthetic method have been developed to produce polycrystalline powders and large single crystals of NH{sub 4}MCl{sub 2}(HCOO) (M=Fe, Co, Ni). The magnetic structure of the 1D linear chain compound NH{sub 4}FeCl{sub 2}(HCOO) has been determined by low-temperature neutron powder diffraction, revealing ferromagnetic intra-chain interactions and antiferromagnetic inter-chain interactions. The newly-reported Co and Ni analogs are isostructural with NH{sub 4}FeCl{sub 2}(HCOO), but there are significant differences in the magnetic properties of each compound; the Ni analog behaves similarly to the Fe compound but with stronger magnetic coupling, exhibiting antiferromagnetic ordering (T{sub N}=8.5 K) and a broad metamagnetic transition between 2 and 5 T, while the Co analog does not order magnetically above 2 K, despite strong antiferromagnetic nearest-neighbor interactions. - Graphical abstract: Large single crystals of NH{sub 4}MCl{sub 2}(HCOO) (M=Fe, Co, Ni), which adopt a 1D zig-zag chain structure, can be grown via a solvothermal method. Neutron diffraction experiments revealed that the magnetic structure of the iron compound exhibits ferromagnetic intra-chain coupling and antiferromagnetic inter-chain coupling. - Highlights: • Large crystals of NH{sub 4}MCl{sub 2}(HCOO) (M=Fe, Co, Ni) have been grown solvothermally. • The magnetic structure of M=Fe was solved by low-temperature neutron diffraction. • NH{sub 4}FeCl{sub 2}(HCOO) exhibits FM intra-chain and AFM inter-chain interactions. • NH{sub 4}CoCl{sub 2}(HCOO) exhibits no 3D magnetic ordering above 2 K. • NH{sub 4}NiCl{sub 2}(HCOO) exhibits AFM ordering (T{sub N}=8.5 K) and FM intra-chain interactions.

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DOE OSTI2016

Synthesis, structure, and magnetic characterization of Cr{sub 4}US{sub 8}

The compound Cr{sub 4}US{sub 8} has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2{sub 1}/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS{sub 6} octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr{sub 4}US{sub 8} is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie–Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength. - Graphical abstract: Structure of Cr{sub 4}US{sub 8} viewed down the a axis. - Highlights: • At 1073 K Cr{sub 4}US{sub 8} was synthesized and at 100 K its crystal structure was determined. • The 3D structure comprises CrS{sub 6} octahedra with channels partially occupied by U. • The magnetic behavior of Cr{sub 4}US{sub 8} is complex.

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DOE OSTI2017

Synthesis and characterization of metastable, 20 nm-sized Pna2{sub 1}-LiCoPO{sub 4} nanospheres

The majority of research activities on LiCoPO{sub 4} are focused on the phospho-olivine (space group Pnma), which is a promising high-voltage cathode material for Li-ion batteries. In contrast, comparably little is known about its metastable Pna2{sub 1} modification. Herein, we present a comprehensive study on the structure–property relationships of 15–20 nm Pna2{sub 1}-LiCoPO{sub 4} nanospheres prepared by a simple microwave-assisted solvothermal process. Unlike previous reports, the results indicate that the compound is non-stoichiometric and shows cation-mixing with Co ions on the Li sites, which provides an explanation for the poor electrochemical performance. Co L{sub 2,3}-edge X-ray absorption spectroscopic data confirm the local tetrahedral symmetry of Co{sup 2+}. Comprehensive studies on the thermal stability using thermogravimetric analysis, differential scanning calorimetry, and in situ powder X-ray diffraction show an exothermic phase transition to olivine Pnma-LiCoPO{sub 4} at 527 °C. The influence of the atmosphere and the particle size on the thermal stability is also investigated. - Graphical abstract: Blue nano-sized Pna2{sub 1}-LiCoPO{sub 4,} featuring tetrahedrally-coordinated Co{sup 2+}, was synthesized in a rapid one-step microwave-assisted solvothermal process. The phase relation between this metastable and the stable polymorph was analyzed and electrochemical properties are discussed. - Highlights: • Preparation of uniform 15–20 nm nanospheres of metastable Pna2{sub 1}-LiCoPO{sub 4} polymorph. • Structure redetermination shows cation-mixing (Co blocking Li sites). • In situ investigation of phase transformation to olivine Pnma-LiCoPO{sub 4} at 527 °C. • Pna2{sub 1}-LiCoPO{sub 4} reemerges as a stable high-temperature phase above 800 °C. • X-ray absorption spectroscopy confirms local tetrahedral symmetry (T{sub d} Co{sup 2+}).

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