Structural Disorder and Molecular Dynamics in Ferroelectric Crystals [C(NH₂)₃]₄Br₂SO₄ and [C(NH₂)₃]₄Cl₂SO₄

Abstract

Two isomorphic ferroelectric crystals of tetraguanidinium dibromo-sulfate, [C­(NH2)3]4Br2SO4, and tetraguanidinium dichloro-sulfate, [C­(NH2)3]4Cl2SO4, have been studied by Raman spectroscopy, single-crystal X-ray diffraction, and scanning calorimetry. Despite the isostructural paraelectric and quasi-isostructural ferroelectric phases, the crystals show distinct phase relations and properties. The differences in the temperature evolution of Raman bands are discussed in terms of thermally activated molecular motions. These results, supported by the temperature-dependent structural and calorimetric data, evidenced that tiny differences in the crystal packing, as well as in the number and strength of hydrogen bonds, are the main factors that determine the crystal thermodynamic behavior and properties. Slightly more loose packing of [C­(NH2)3]4Br2SO4 results in the structural disorder activated well below the transition point and contributes to the fact that thermodynamically first-order transition acquires some features of second-order transition.

Nanoscale Effects in One‐Dimensional Columnar Supramolecular Ferroelectrics

“…On the contrary, practically all applicable inorganic ferroelectrics have several problems to overcome, such as toxicity, heavy weight, rare metal utilization, device fabrication cost, and others. The development of organic ferroelectrics is one of the potential approaches that might solve the above problems simultaneously, and a variety of organic materials have been developed in the areas of charge transfer, hydrogen bonding, simple cation‐anion exchange, and organic–inorganic hybrid crystals . A higher degree of design freedom for organic materials than that for the inorganic ones can allow facile expansion of the variety of materials and also mechanisms with which the order–disorder polarization inversion, such as proton transfer and supramolecular rotator, stores bits …”

“…The development of organic ferroelectrics is one of the potential approaches that might solve the above problems simultaneously,a nd av ariety of organic materials have been developed in the areas of charget ransfer,h ydrogen bonding, simple cation-anion exchange, and organic-inorganic hybrid crystals. [4][5][6][7][8][9][10] Ah igher degree of design freedom for organic materials than that for the inorganic ones can allow facile expansion of the varietyo fm aterials and also mechanisms with which the order-disorder polarizationi nversion,s uch as proton transfer and supramolecular rotator, stores bits. [11,12] Both the remanentp olarization (P r )a nd the coercive electric field (E c )a re important as the typicalf erroelectric parameters, which are associated with the ON/OFF ratio of as witching event,a nd an applied voltage in the memory device, respectively.F or instance, both the P r = 21 mCcm À2 and the E c = 29 kV cm À1 values of single-crystal croconic acid is superior to that of the P r = 15 mCcm À2 and E c = 85 kV cm À1 values for PZT.…”