FULLERIDE SUPERCONDUCTORS AND ORIENTATIONAL ORDER - T-C VS LATTICE-CONSTANT IN NA2RBXCS1-XC60

The effect of orientational order on fulleride superconductivity was s tudied by performing DC SQUID magnetometry and high-resolution x-ray d iffraction on the title quaternary phases. These are all simple cubic, Pa (3) over bar space group, with the same molecular orientational or der as occurs in pure C-60. The T-c vs. lattice constant correlation i s much steeper than is found for the merohedrally-disordered Fm (3) ov er bar m phases, implying the possibility of large T-c enhancements wi th only minor additional dilation of the sc lattice. The effect of ori entational order can be rationalized as primarily due to a density of states effect.