Calorimetric and dielectric study of organic ferroelectrics, phenazine-chloranilic acid, and its bromo analog.

The heat capacities of single crystals of organic ferroelectric complexes phenazine-chloranilic acid (Phz-H(2)ca) and phenazine-bromanilic acid (Phz-H(2)ba) were measured. At temperatures below those of the reported ferroelectric phase transitions, heat capacity anomalies due to successive phase transitions were found in both complexes. Excess entropies involved in the low-temperature successive phase transitions are much larger than those due to the ferroelectric phase transitions. The temperature dependence of the complex dielectric constants showed the existence of multiple dielectric relaxation modes in both complexes and their deuterated analogs (Phz-D(2)ca and Phz-D(2)ba). We discuss the possibility of concerted hopping of neighboring protons within a hydrogen-bonded chain while taking into account the one-dimensional nature of the chain.