SUPERCONDUCTIVITY IN ALKALI-AMMONIA COMPLEX FULLERIDES

Here we show that low temperature synthesis in liquid ammonia successf ully stablied the combination of one Na and two large alkali ions (K a nd Rb) by incorporating NH3 molecules. Both (NH3)(x)NaK2C60 and (NH3)( x)NaRb2C60 (x similar to 0.8) retained the fee cell with a=14.37 Angst rom and a=13.52 Angstrom, and superconduct at 11K and 13K, respectivel y, A Na-NH3 cluster occupies the octahedral interstice and remaining K or Rb occupies the tetrahedral site. The Na ion is displaced by 0.4-0 .6 Angstrom from the center of the octahedral site. The present system thus provides an example of fee superconductors involving off-centere d cations that exhibit different trend in the well known relationship between transition temperature (T-c) and lattice parameter of face-cen tered cubic A(3)C(60) (A=alkali metals) superconductors.(1-3)