Abstract
Alkali-metal-doped fullerenes are prepared by a rapid, new method employing alkali-metal azides. By means of ac susceptibility and low-field microwave absorption (LFMA), the authors have investigated the superconducting phases in K- and Rb-doped C. With Rb doping, the transition to the superconducting state takes place at T{sub c} = 38 K when observed by LFMA. The LFMA signal shows significant hysteresis behavior. During a day following the doping process, the LFMA for nominal composition Rb{sub 3}C{sub 60} is found to be drastically time dependent. Measurements by ac susceptibility, on the same sample, show an onset at 34 K which is lower than the T{sub c} obtained by LFMA but higher than the highest value reported for Rb{sub 3}C{sub 60} by ac susceptibility. This could indicate the presence of another superconducting phase. At 12 K the superconducting fraction is found to be about 95% by ac susceptibility so the material formed by this new preparation method is almost entirely superconducting. 22 refs., 4 figs., 1 tab.
Published Version
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