H. Shimoda et al., SUPERCONDUCTIVITY IN ALKALI-AMMONIA COMPLEX FULLERIDES, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 285, 1996, pp. 181-186
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)