A one-step doping process of C~o crystals with three equivalents of rubidium to produce Rb3C~o crystals was developed. The Tc's for all Rb3C6o crystalline samples ( ~ 30.5 K) were higher than those of the powder samples (28 to 29.6 K), but consistent with the reported four-probe resistivity result for a doped C6o crystal (transition midpoint = 30.2 K). High superconducting shielding fractions (between 60 and 90%) and sharp magnetic transition widths (ATlo-9o between ~ 3 K and 0.7 K) were observed for the samples doped with Rb at temperatures of 300 to 450°C. The doping process, as well as the composition, of these samples were studied with the use of an ESR spectrometer. Two major components, RbC~o and Rb3C~o, were quantitatively characterized. The superconducting shielding fractions of these samples were found to be linearly correlated with the Rb3C~o content obtained from ESR measurements. Higher-temperature doping ( > 400 °C) favored the formation of Rb3C~o at the expense of severe C~o crystal fragmentation. The optimal doping condition to produce Rb3C~o crystals was found to be around 300 ° C.
Synthesis, Purification, and Characterization of the 1:1 Addition Product of C60 and Anthracene. --(SCHLUETER, J. A.; SEAMAN, J. M.; TAHA, S.; COHEN, H.; LYKKE, K. R.; WANG, H. H.; WILLIAMS, J. M.; J.
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