Isothermal relaxation of discommensurations in K2ZnCl4

Overview & Synopsis

At the incommensurate-ferroelectric transition temperature Tc of K2ZnCl4, the dielectric susceptibility contains an anomalous contribution both above and below Tc. Previous quasi-static dielectric measurements and hysteresis loops demonstrated that this anomalous part arises from the peculiar dynamics of discommensurations. We have used isothermal dielectric measurements to get some insight into the long time dynamics of these discommensurations. We have found that the characteristic relaxation times τ are of the order of 104 s in the incommensurate and in the ferroelectric phase. Even more unusual is a non-monotonous relaxation which is observed in a restricted temperature range above and below Tc. In agreement with previous results in Rb2ZnCl4, this is ascribed to the pinning of discommensurations by defects. We show, for the first time, that the crossover time of this peculiar relaxation increases drastically at the same temperature under either heating or cooling conditions.