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

Abstract

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.

New Organic Ferroelectrics: Cocrystal of 5,5′-Dimethyl-2,2′-bipyridine and Bromanilic Acid

“…below the second-order phase transition has been observed in PhzH 2 ca and its analogs. 10,11 Although a similar situation may be imagined, this issue is left for the future.…”

“…Such H-bond chains often exhibit interesting dynamics of protons, which is, e.g., seen in PhzH 2 ca. 11 However, the study on the proton dynamics in 55DMBPH 2 ba is beyond the scope of the present work.…”

Thin films of a ferroelectric phenazine/chloranilic acid organic cocrystal

“…Phz-H 2 ca cocrystal bulk powder similarly has a peak in the dielectric constant and loss at reduced temperatures [7,19]. Disorder in the Phz-H 2 ca cocrystal thin films may be responsible for the shift and broadening of the dielectric constant peak and the associated paraelectric-ferroelectric phase transition.…”

Cell-quintupling: Structural phase transition in a molecular crystal, bis(trans-4–butylcyclohexyl)methanol

“…Phase transitions between crystalline phases having closely related structures are widely involved in the evolution of materials functionality such as ferroelectricity. [1][2][3] Such phase transitions offer the stage for detailed discussions in the context of the group theory first proposed by Landau 4 (Landau's thermodynamic phenomenology). Landau's phenomenology puts forward the criteria that govern the possible occurrence of a continuous transition.…”