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A new solid-state 19 F magic-angle spinning NMR signal at an isotropic 19 F chemical shift of −53 ppm is measured from graphite fluoride synthesized by reaction of graphite with F 2 at temperatures above 750 K with no catalyst. Two-dimensional NMR suggests the −53 ppm 19 F NMR signal originates from covalent fluoromethanetriyl groups belonging to ordered (C y F) n bulk domains composited with the major (CF) n domains. Quantitative 19 F and 13 C NMR find y = 4.32 ± 0.64 . DFT calculations of NMR chemical shifts for unsaturated fluorographene models show that a (C 4 F) n phase with fluorine bound covalently to a single side of the carbon layer best explains the observed NMR chemical shifts. We assign the new phase to this (C 4 F) n structure, which constitutes up to 15% of the carbon in our graphite fluoride composites. The (C 4 F) n content of the composite affects bulk electrochemical properties in a manner similar to graphite fluorides produced by conventional, catalyzed fluorination processes. [ABSTRACT FROM AUTHOR]

Nanoparticle dispersions of various phases were added to YBa2Cu3O7-x (YBCO or 123) thin films by multilayer pulsed laser deposition, to determine their effect on flux pinning. The different pinning materials examined include Y2BaCuO2 (Y211 or green-phase), La2BaCuO2 (La211 or brown-phase), Y2O3, CeO2, and MgO, with lattice constant mismatches varying from 0.5% to 12% with respect to YBCO. Y211 and Y2O3 provided significant pinning increases at temperatures of 65 K and 77 K, however other phases provided enhancements only at 65 K (for CeO2 and La211) for limited range of applied field strengths. An interesting correlation between Tc transition widths and pinning strengths was observed. The additions produced markedly different nanoparticle and film microstructures, as well as superconducting properties. [ABSTRACT FROM AUTHOR]