Synthesisand properties of C_<60> based mutielement compounds

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We have carried out a fundamental research on fullerene based solids and obtained the following results.1. Fullerene polymersWe have succeeded to selectively synthesize a fullerene dimer, which is a 2+2 cycloadduct of C60, by a high pressure-high temperature treatment of a molecular compound(ET)2C60. Comparing the dimer, one-dimensional polymer, and two-dimensional polymers by means of differential scanning calorimetry measurements, we clarified that all the polymeric forms of fullerenes are more stable than the monomer form. The energetics of the fullerene polymers are established in this work. The energy difference between these polymeric phases are smaller than the difference between graphite and diamond.2.Multinary fullerene superconductors2-1 : Antiferromagnetic order in NH3K3C6OSuperconductor-insulator transition is one of the universal and fundamental problems in solid state physics.In the case of fullerenes, this transition takes place by an intercalation of NH3 molecules into … More superconducting K3C60. We have investigated the nonsuperconducting NH3K3C6O by various means to clarify the mechanism of superconductor-nonsuperconductor transition. We found that the electronic ground state of NH3K3C6O is an antiferromagnetic insulator. This result clearly shows that he loss of superconductivity in NH3K3C6O is of magnetic origin, providing a nice analogy to the well know cuprate and organic superconductors.2-2 : High pressure effect of (NH3)xNaA2C6O(O.5<x<l, A=K, Rb)superconductorsThe title superconductors shows an anomalous correlation between Tc and lattice parameter, which is opposite to the one found in the standard A3C60 superconductors. The Tc/llattice parameter correlation was investigated under hydrostatic pressure, showing that Tc of these ammoniated superconductors is not scaled any more simply by the interfullerene spacings.2-3 : Superconductor at highly doped statesNew fullerene superconductors with highly doped states are found. The nonavalent K3Ba3C6O and decavalent K2Ba4C6Oshowed that the criterion of superconductivity in the highly doped state is significantly different form that of the low doped systems. Less