The dielectric properties of polycrystalline C₆₀

The dielectric properties (1-50 kHz) of polycrystalline C60have been carefully studied from 70 to 300 K. Below 170 K, the ac conductance σ(T) is proportional to the temperature, which is thought to be due to the phonon-assisted jump of electrons between localized states around the Fermi level. A significant change of the slope of the capacitance versus temperature curve occurs at 85 K, which can be attributed to the glass transition. It is confirmed that electric dipoles may be induced by orientational defects in C60crystal. The capacitance drop around 256 K is found to originate from the disappearance of the orientational defects above the order-disorder phase-transition temperature.