• An Erratum to this article was published on 31 October 1991


SUPERCONDUCTING K3C60 (ref. 1) has been shown2 to have an intercalated face-centred cubic (f.c.c.) structure, and other A3C60 compounds (where A is K, Rb or mixtures of K, Rb and/or Cs) form an isostructural series with superconducting transition temperatures up to 31.3 K (ref. 3). Recently we reported413C NMR studies of KxC60 for x<3, and concluded that the system contained two phases (x = 0 and x = 3) for 0<x<3. Here we report an investigation of AxC60 in the range 3<x<6 and find evidence for an additional phase at x = 4. In contrast to f.c.c. A3C60 (refs 2, 3) and body-centred cubic A6C60 (ref. 5), A4C60 (where A is K, Rb, Cs) has a body-centred tetragonal structure. We show that all of the experimentally observed phases of AxC60 can be predicted solely on the basis of electrostatic considerations. We have found no evidence for superconductivity in A4C60.

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  1. 1

    Hebard, A. F. et al. Nature 350, 600–601 (1991).

  2. 2

    Stephens, P. W. et al. Nature 351, 632–634 (1991).

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    Fleming, R. M. et al. Nature (in the press).

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    Tycko, R. et al. Science (in the press).

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    Fleming, R. M. et al. in Clusters and Cluster Assembled Materials (ed. Averback, R. S.) (Materials Research Society, New York, 1991).

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  1. AT&T Bell Laboratories, Murray Hill, New Jersey, 07974, USA

    • R. M. Fleming
    • , M. J. Rosseinsky
    • , A. P. Ramirez
    • , D. W. Murphy
    • , J. C. Tully
    • , R. C. Haddon
    • , T. Siegrist
    • , R. Tycko
    • , S. H. Glarum
    • , P. Marsh
    • , G. Dabbagh
    • , S. M. Zahurak
    • , A. V. Makhija
    •  & C. Hampton


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