Low-frequency dielectric relaxations of a nonchiral liquid crystal, 8CB

Low-frequency dielectric measurements are performed on a nonchiral liquid c rystal (8CB) for two different cell thicknesses 4.5 mum and 1.6 mum, as fun ctions of temperature at various amplitudes of the probe field. Relaxation peak frequencies are observed at similar to 10 Hz for the 4.5 mum thick sam ple and similar to 100 Hz for the 1.6 mum cell. When the external-field amp litude was increased, the relaxation peak frequency was shifted to lower fr equency for the 4.5 mum cell but hardly changed for the 1.6 mum cell. To ex plain this odd result from experimental observations, we performed a numeri cal simulation, where the ionic impurities were assumed to encounter ioniza tion-recombination processes in addition to a translational diffusion. We w ere able to confirm that there are two separate contributions from ionic im purities to the low-frequency dielectric relaxations in this system-that is , from fast ions in the single-particle diffusion and slow ions in the ioni zation-recombination-assisted diffusion.