Electrical Resistivity of Fullerenes at High Pressures

Abstract

We have measured the electrical resistivity as a function of temperature up to pressures of 25 GPa of pure fullerenes C60, C70 and the compound C60I4. For the three materials the best fit in our temperature range corresponds to a three-dimensional variable-range hopping conductivity, signature of an important disorder. A dramatic decrease of the resistivity, by two orders of magnitude per GPa, is observed at low pressures. However, no metallic state is attained as all the samples present a phase transformation in the high-pressure range, probably originated by the crossover from sp2 to sp3 hybridization of the carbon orbitals at high pressures.