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首页> 外文期刊>Chemistry: A European journal >Structure-Property Relationship of Supramolecular Ferroelectric [H-66dmbp][Hca] Accompanied by High Polarization, Competing Structural Phases, and Polymorphs
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Structure-Property Relationship of Supramolecular Ferroelectric [H-66dmbp][Hca] Accompanied by High Polarization, Competing Structural Phases, and Polymorphs

机译：超分子铁电[H-66dmbp] [Hca]的结构-性质关系与高极化，竞争的结构相和多晶型物

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摘要

Three polymorphic forms of 6,6'-dimethyl-2,2'-bi-pyridinium chloranilate crystals were characterized to understand the origin of polarization properties and the thermal stability of ferroelectricity. According to the temperature-dependent permittivity, differential scanning calorimetry, and X-ray diffraction, structural phase transitions were found in all polymorphs. Notably, the ferroelectric alpha-form crystal, which has the longest hydrogen bond (2.95 angstrom) among the organic acid/base-type supramolecular ferroelectrics, transformed from a polar structure (space group, P2(1)) into an anti-polar structure (space group, P2(1)/c) at 378 K. The non-ferroelectric beta- and gamma-form crystals also exhibited structural rearrangements around hydrogen bonds. The hydrogen-bonded geometry and ferroelectric properties were compared with other supramolecular ferroelectrics. A positive relationship between the phase-transition temperature (T-c) and hydrogen-bond length () was observed, and was attributed to the potential barrier height for proton off-centering or order/disorder phenomena. The optimized spontaneous polarization (P-s) agreed well with the results of the first-principles calculations, and could be amplified by separating the two equilibrium positions of protons with increasing . These data consistently demonstrated that stretching is a promising way to enhance the polarization performance and thermal stability of hydrogen-bonded organic ferroelectrics.
机译：表征了6,6'-二甲基-2,2'-氯吡啶鎓吡啶鎓晶体的三种多晶型形式，以了解极化性质的起源和铁电的热稳定性。根据与温度有关的介电常数，差示扫描量热法和X射线衍射，在所有多晶型物中都发现了结构相变。值得注意的是，在有机酸/碱型超分子铁电体中具有最长氢键（2.95埃）的铁电体α型晶体从极性结构（空间群P2（1））转变为反极性结构（空间群，P2（1）/ c）在378K。非铁电的β型和γ型晶体还表现出围绕氢键的结构重排。将氢键的几何形状和铁电性质与其他超分子铁电体进行了比较。观察到相变温度（T-c）与氢键长度（）之间呈正相关，这归因于质子偏心或有序/无序现象的势垒高度。优化的自发极化（P-s）与第一性原理计算的结果非常吻合，并且可以通过增加d分离质子的两个平衡位置来进行放大。这些数据一致地表明，拉伸是增强氢键合有机铁电体的极化性能和热稳定性的有前途的方法。

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