Synthesis of LixC60(x=1–28) fullerides under high-pressure and high-temperature conditions and their electrical properties

LixC60 with compositions of x=1–28 were treated under 5 GPa at 573 K for 1 h in order to explore a new Li-doped C60 polymer. Three types of Li-doped phases, i.e., trigonal (3R) two-dimensional (2D-) polymer, tetragonal (T) 2D-polymer, and fcc monomer were obtained as single phases for x=1,4,16, respectively by the high-pressure (HP) treatment. The C60 molecules in the 3R and T 2D-polymers are linked via [2+2] cycloaddition at a distance of 9.3 Å. Li4C60 prepared without the HP treatment was a new T 2D-polymer linked by the [2+2] cycloaddition. The IR spectra of the Li4C60 and the Li16C60 before and after the HP treatment suggested the existence of some degrees of covalency between the Li and C atoms. The electrical conductivity measurements showed that the (LiC60)HP 3R 2D-polymer, the (Li4C60)HP T 2D-polymer, and the (Li16C60)HP fcc monomer phases were semiconductors with the conductivities of 1.8×10−4, 1.2×10−1, 6.4×10−1 Ω−1 cm−1 at room temperature, respectively.