LOW-FREQUENCY DIELECTRIC PERMITTIVITY OF C-60

Complex dielectric response measurements have been made on a C-60/C-70 mixture pellet. The frequency and temperature ranges cover from 20 Hz to 1 MHz and from 30 to 300 K. Results show that the real part of the dielectric constant is 5 with a weak thermally activated polarization contribution. This thermal polarization is believed to be related to reorientation of C-60 molecules recently observed by many techniques s uch as NMR, sound velocity, thermal conductivity, and others. Our data yield relaxation frequencies for reorientation, indicating that the p resence of an additional electric dipole moment of the orientationally ordered C-60 molecules at low temperature contributes 0.2-0.3 to the static dielectric constant.