Solid State Molecular Dynamic Investigation of An Inclusion Ferroelectric: [(2,6-Diisopropylanilinium)([18]crown-6)]BF4

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• 作者：Heng-Yun Ye ; Shen-Hui Li ; Yi Zhang ; Lei Zhou ; Feng Deng ; Ren-Gen Xiong
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：July 16, 2014
• 年：2014
• 卷：136
• 期：28
• 页码：10033-10040
• 全文大小：636K
• ISSN：1520-5126

文摘

Many order鈥揹isorder-type phase transitions in molecule-based ferroelectrics are related to changes of molecular dynamics. If the molecular motions do not involve reorientations of dipole moments, their ordering fails to contribute directly to spontaneous electric polarization. For understanding ferroelectric mechanisms in these systems, it is important to clarify how such molecular dynamics changes induce structurally symmetry-breaking phase transitions and thus the appearance of spontaneous electric polarization. Systematic characterization of an [18]crown-6 based host鈥揼uest inclusion compound, [(DIPA)([18]crown-6)]BF₄ (DIPA = 2,6-diisopropylanilinium), shows it is an excellent ferroelectric with a large dielectric anomaly, significant pyroelectricity, and SHG response, and rectangular polarizaiton鈥揺lectric field hysterisis loops. By the combination of variable-temperature single-crystal structural determination and solid-state NMR observation, it is found that the slowing down of the rotation of the [18]crown-6 molecule and the tumbling of the BF₄ anion causes the symmetry breaking, while the spontaneous polarization is induced by the relative displacement between the cationic and anionic sublattices. This investigation will contribute to a deeper understanding of the structure鈥損roperty relationship in the emerging molecular ferroelectrics.