New Organic Ferroelectrics: Co-crystal of 5,5'-Dimethyl-2,2'-bipyridine and Bromanilic Acid

Yasuhisa YAMAMURA, Erika SAITO, Hideki SAITOH, Norie HOSHINO and Kazuya SAITO

Co-crystal 55DMBP-H2ba was synthesized and characterized. The crystral structure is isostructural to co-crystal 55DMBP-H2ia with iodanilic acid. The heat capacity, dielectic permittivity, and polarization-electric field hysteresis showed that the 55DMBP-H2ba undergoes a paraelectiric-ferroelectic phase transition at 253 K on cooling. The transition mechanism is discussed through the analysis of isotropic temperature factors of atoms.
(Chem. Lett., 41, 119 (2012))

Calorimetric and Dielectric Study of Organic Ferroelectrics, Phenazine-Chloranilic Acid and Its Bromo Analogue

Masakazu AMANO, Yasuhisa YAMAMURA, Masato SUMITA, Syuma YASUZUKA, Hitoshi KAWAJI, Tooru ATAKE and Kazuya SAITO

The heat capacities of single crystals of organic ferroelectric complexes phenazine-chloranilic acid Phz-H2ca and phenazine-bromanilic acid Phz-H2ba 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-D2ca and Phz-D2ba . 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.
(J. Chem. Phys., 130, 034503 (2009))

One-Dimensional Correlation in the Dipolar Ising Crystal Tricyclohexylmethanol: Crystal Structure Revisited and Heat Capacity

Yasuhisa YAMAMURA, Hideki SAITOH, Masato SUMITA and Kazuya SAITO

The crystal structure of an organic weak-ferroelectrics, tricyclohexylmethanol (TCHM), was re-examined by single-crystal x-ray diffraction at room temperature. TCHM forms a dimer through hydrogen bonding at the centre of the dimer, where two hydroxyl groups are arranged in tandem and their direction is disordered in two possible orientations, which brings about a dipolar Ising nature. The heat capacity measured by adiabatic calorimetry from 6 to 400 K shows three anomalies including fusion at 368 K. The entropy of the ferroelectric transition is 1.9 J K-1 mol-1, supporting the order-disorder mechanism of dimer dipoles. A broad anomaly at 348 K is related to the breakage of the intra-dimer hydrogen bond. Detailed analysis of the temperature dependence of heat capacity due to the phase transition showed the presence of a broad hump in the excess heat capacity around 160 K. The temperature dependences of the excess heat capacity and the existing dielectric constant can be analysed in terms of a highly anisotropic Ising model.
(J. Phys. Condensed Matt., 19, 176219 (2007))

Low-Temperature Phase Transitions of an Organic Ferroelectrics, Phenazine-Chloranilic Acid

Kazuya SAITO, Masakazu AMANO, Yasuhisa YAMAMURA, Takeo TOJO and Tooru ATAKE

The heat capacity of a ferroelectrics consisting of two organic components having a centrosymmetric molecular shape, phenazine-chloranilic acid, was precisely measured by adiabatic calorimetry below room temperature. The paraelectric-ferroelectric phase transition was detected at 248 K as a heat capacity anomaly. The excess entropy involved is consistent with the previously assumed displacive nature. In addition to the ferroelectric phase transition, two phase transitions were observed in heat capacity and dielectric constant at 136 K and 146 K.
(J. Phys. Soc. Jpn., 75, 033601 (2006))

Successive Phase Transitions of p-Methylbenzyl Alcohol Crystal Studied by X-ray Diffraction and Adiabatic Calorimetry: Structural Disorder in Room-Temperature Phase

Hideki SAITOH, Satoaki IKEUCHI and Kazuya SAITO

Crystal structures of the room-temperature (RT) and low-temperature (LT) phases of p-methylbenzyl alcohol were reexamined by single-crystal X-ray diffraction method while paying special attention to detect structural disorder in the RT phase involved in successive structural phase transitions at 179 K and 210 K. In the RT phase at 250 K, positional disorder of oxygen atoms was detected in contrast to the previous structure report. The structure of the LT phase coincided to the previous one. Heat capacities were measured by adiabatic calorimetry below 350 K, which covers the structural phase transitions and fusion at 331.87 K. The structural phase transitions were of first-order and required long time for completion. The combined magnitude of entropies of transition was ca. 5 J K-1 mol-1, a part of which can be ascribed to the positional disorder observed in the structure analysis. Standard thermodynamic functions are tabulated below 350 K.
(J. Therm. Anal. Calor., 81, 511 (2005))

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