Switchable Dielectric Phase Transition Induced by Ordering of Twisting Motion in 1,4-Diazabicyclo[2.2.2]octane Chlorodifluoroacetate

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• 作者：Xiaojun Shi ; Junhua Luo ; Zhihua Sun ; Shigeng Li ; Chengmin Ji ; Lina Li ; Liang Han ; Shuquan Zhang ; Daqiang Yuan ; Maochun Hong
• 刊名：Crystal Growth & Design
• 出版年：2013
• 出版时间：May 1, 2013
• 年：2013
• 卷：13
• 期：5
• 页码：2081-2086
• 全文大小：510K
• 年卷期：v.13,no.5(May 1, 2013)
• ISSN：1528-7505

文摘

A novel molecular electric ordered compound [(Hdabco)⁺ClF₂CCOO^{鈥?/sup>] (complex 1, dabco = 1,4-diazabicyclo[2.2.2]octane) has been discovered as a switchable dielectric material, in which the N鈥揌路路路O hydrogen bonds connect the anions and cations together to form a dimer structure. It undergoes a reversible second order solid state phase transition at 165 K (T_c), which was confirmed by thermal analyses including differential scanning calorimetry (DSC) and specific heat (C_p) and dielectric measurements. Variable temperature single crystal X-ray diffraction analyses revealed its order鈥揹isorder transformation of twisting motion characteristic behaviors for the phase transition. Owing to the ordering of twisting motions of the chlorodifluoroacetate anions, the structure of 1 demonstrates a phase transition from high crystallographic symmetry with space group of Pnma to the low state with space group of P2₁/c; that is, an Aizu notion of mmmF2/m occurs. Emphatically, the dielectric constant of 1 displays a distinctive step-like anomaly; namely, it possesses a high dielectric state in the room temperature phase (RTP) and a low state in the low temperature phase (LTP). Such distinctive dielectric performances disclose that 1 might be considered as a potential switchable dielectric material. We believe that all the findings would afford a useful strategy in exploring new electric ordering materials.}