STRUCTURE AND PROPERTIES OF ALKALI-DOPED C-60

The structure of superconducting face-centered cubic (f.c.c.) M3C60 compounds has been precisely studied for binary alkali-metal-doped C60 molecules, where M is Na, K, Rb, Cs and their binary mixtures. Refinements of the observed X-ray diffraction patterns show that MS2MLC60 compounds are stable and preferentially ordered compared with the crystal phases for MSML2C60, which are very dependent on the alkali metals used, where M(S) denotes the smaller alkali metal and M(L) the larger metal. A new relationship between the superconducting transition temperature (T(c)) and the f.c.c. lattice constant (a0) is demonstrated over a wide range of lattice parameters, using the binary alkali-metal-doped f.c.c. M3C60 superconductors. The new T(c)-a0 relationship is compared with the previously reported pressure experiments and the prediction based on the simple Bardeen-Cooper-Schriefter theory.