Low-temperature dielectric relaxation in ferroelectric pyridinium tetrafluoroborate

The dielectric behavior of polycrystalline pyridinium tetrafluoroborate, C5NH6BF4, has been investigated in detail at temperatures in the range of 120 K a parts per thousand currency sign T a parts per thousand currency sign 280 K and frequencies in the range of 10 Hz a parts per thousand currency sign nu a parts per thousand currency sign 10(5) Hz. The marked dielectric dispersion observed at temperatures below 205 K was analyzed by using the sum of two different relaxation processes. The temperature dependence of the relaxation time for the main one with dominant strength revealed an excellent fit to the Arrhenius equation with an activation energy E = 2702 +/- 6 K and a pre-exponential factor tau(0) = 2.2 x 10(-11) s. The coupled reorienting motion of the pyridinium cation and the BF4 anion is suggested to account for the main process. The relaxation time for the other weak process also obeys the Arrhenius law with E = 815 +/- 14 K and tau(0) = 7.9x10(-5) s. The origin of the weak process is ascribed to the ferroelectric domain-wall motion.