Ac conductivity and dielectric constant in (NbSe 4) 10/3I and (TaSe 4) 2I

Abstract

Temperature dependence of the ac conductivity of (NbSe 4) 10/3I and (TaSe 4) 2I has been measured in the frequency range 10 Hz-10 MHz in the charge-density-wave states. Just below the transition temperature T c= 289 K, the dielectric constant suddenly increases and shows a maximum around 265 K in (NbSe 4) 10/3I. On the other hand, well below T c=263 K the dielectric constant increases and has a maximum around 190 K in (TaSe 4) 2I. Strong frequency dependence is observed in their dielectric constants. The imaginary part of the conductivity of (NbSe 4) 10/3I as a function of the frequency shows a peak just below T c. It shifts to higher frequency with decreasing temperature. Below about 200 K a low-frequency relaxation process proposed by Cava et al. was observed in both compounds.