K3+δC84.: Higher fullerene analogues of the A3C60 superconductors

Face-centered cubic phases of both the D-2 and D-2d isomers of the C-84 anion with band fillings close to those of the A(3)C(60) superconductors are prepared by a two-step reaction involving saturated K8+xC84 phases as intermediates. Rietveld refinement shows that the structures are more disordered than those of K8+xC84, with incomplete occupancy of multiple cation sites and the presence of two anion orientations, while both temperature-dependent powder diffraction and EPR demonstrate the monophasic nature of the reaction products. The temperature-independent magnetic susceptibilities and line width variation in EPR indicate that these phases have finite densities of states at the Fermi level for both C-84 majority isomers, unlike the previously prepared saturated phases, but de magnetization measurements indicate the absence of superconductivity above 5 K.