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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Epitaxial crystals of Bi{sub 2}Pt{sub 2}O{sub 7} pyrochlore through the transformation of δ–Bi{sub 2}O{sub 3} fluorite

Bi{sub 2}Pt{sub 2}O{sub 7} pyrochlore is thought to be one of the most promising oxide catalysts for application in fuel cell technology. Unfortunately, direct film growth of Bi{sub 2}Pt{sub 2}O{sub 7} has not yet been achieved, owing to the difficulty of oxidizing platinum metal in the precursor material to Pt{sup 4+}. In this work, in order to induce oxidation of the platinum, we annealed pulsed laser deposited films consisting of epitaxial δ–Bi{sub 2}O{sub 3} and co-deposited, comparatively disordered platinum. We present synchrotron x-ray diffraction results that show the nonuniform annealed films contain the first epitaxial crystals of Bi{sub 2}Pt{sub 2}O{sub 7}. We also visualized the pyrochlore structure by scanning transmission electron microscopy, and observed ordered cation vacancies in the epitaxial crystals formed in a bismuth-rich film but not in those formed in a platinum-rich film. The similarity between the δ–Bi{sub 2}O{sub 3} and Bi{sub 2}Pt{sub 2}O{sub 7} structures appears to facilitate the pyrochlore formation. These results provide the only route to date for the formation of epitaxial Bi{sub 2}Pt{sub 2}O{sub 7}.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Pressure-induced phase and chemical transformations of lithium peroxide (Li 2 O 2 )

Here, we present the pressure-induced phase/chemical changes of lithium peroxide (Li 2 O 2 ) to 63 GPa using diamond anvil cells, confocal micro-Raman spectroscopy, and synchrotron x-ray diffraction. The Raman data show the emergence of the major vibrational peaks associated with O 2 above 30 GPa, indicating the subsequent pressure-induced reversible chemical decomposition (disassociation) in dense Li 2 O 2 . The x-ray diffraction data of Li 2 O 2 , on the other hand, show no dramatic structural change but remain well within a P6 3 /mmc structure to 63 GPa. Nevertheless, the Rietveld refinement indicates a subtle change in the structural order parameter z of the oxygen position O (1/3, 2/3, z) at around 35 GPa, which can be considered as a second-order, isostructural phase transition. The nearest oxygen-oxygen distance collapses from 1.56 Å at ambient condition to 1.48 Å at 63 GPa, resulting in a more ionic character of this layered crystal lattice, 3Li + +(LiO 2 )$3-\atop{3}$. This structural change in turn advocates that Li 2 O 2 decomposes to 2Li and O 2 , further augmented by the densification in specific molar volumes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗