An attempt to prepare carbon clathrate compounds using high-pressure and high-temperature conditions

In an attempt to prepare a crystalline carbon compound having a three-dimensional (3D) network similar to silicon clathrate superconductors, fullerene C60 molecules were three-dimensionally polymerized using high-pressure and high-temperature conditions. A single crystal of 3D polymer was obtained from a two-dimensional C60 polymer with a body-centered orthorhombic symmetry. The X-ray structural analysis of the 3D polymer revealed that the spherical C60 monomer molecules were substantially deformed to cuboidal shapes, each unit being bonded to eight neighboring units to form a body-centered orthorhombic lattice. The new 3D polymer was electrically conductive and showed high micro-Vickers hardness comparable to that of cubic BN.