The locations of alkali cations in alkali-metal-fullerides

We study the locations of alkali cations in alkali-metal-fullerides by calc ulating the interaction between alkali cations and C-60 molecules, which co nsists of short-range interatomic (ionic) potentials and long-range Coulomb interaction. It is shown that the octahedrally coordinated alkali cations shift away from the center along the [111] directions in some FCC alkali fu llerides A(3)C(60) and A(x)A(y)'C-60 (x + y = 3), while those in other alka li fullerides, with a higher-content of alkali cations, such as A(4)C(60) a nd A(6)C(60), shift along the [110] directions, whereas for these compounds the alkali cations in the tetrahedral sites remain in the central position s. The calculation also show that the octahedral sites, as well as the tetr ahedral sites, are not all equivalent because the transition from FCC phase to orientationally ordered phase break the FCC symmetry of the lattice. (C ) 2000 Elsevier Science B.V. All rights reserved.