Unusual High-Temperature Reversible Phase-Transition Behavior, Structures, and Dielectric鈥揊erroelectric Properties of Two New Crown Ether Clathrates

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• 作者：Yun-Zhi Tang ; Yin-Mei Yu ; Jian-Bo Xiong ; Yu-Hui Tan ; He-Rui Wen
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：October 21, 2015
• 年：2015
• 卷：137
• 期：41
• 页码：13345-13351
• 全文大小：450K
• ISSN：1520-5126

文摘

Molecular ferroelectrics with high-temperature reversible phase-transition behaviors are very rare and have currently become one of the hotspots in the field of ferroelectric materials. Herein we display two new crown ether clathrates possessing unusual high-temperature ferroelectric phase-transition behaviors, cyclohexyl ammonium 18-crown-6 tetrafluoroborate (or perchlorate), [Hcha-(18-crown-6)]⁺ [BF₄]^{鈭?/sup> (1) and [Hcha-(18-crown-6)]+[ClO₄]鈭?/sup> (2) (Hcha = protonated cyclohexyl ammonium). We have proven their reversible structural phase transitions by variable-temperature PXRD measurements and temperature evolutions of Raman bands. Both clathrates exhibit clear ferroelectric phase transitions at about 397 and 390 K, respectively, revealed by the thermal anomalies of differential scanning calorimetry (DSC) measurements, together with abrupt dielectric anomalies in the heating and cooling processes. The measurements on ferroelectric properties using the single crystals showed optimized spontaneous polarization (P_s) of ca. 3.27 渭C cm鈥? for 1 and 3.78 渭C cm鈥? for 2.}