Wang Zhong-Xia, Zhang Yi, Tang Yuan-Yuan, Li Peng-Fei, Xiong Ren-Gen
Ordered Matter Science Research Center , Nanchang University , Nanchang 330031 , People's Republic of China.
Jiangsu Key Laboratory for Science and Applications of Molecular Ferroelectrics , Southeast University , Nanjing 211189 , People's Republic of China.
J Am Chem Soc. 2019 Mar 13;141(10):4372-4378. doi: 10.1021/jacs.8b13109. Epub 2019 Mar 5.
Antiperovskites have developed to be one kind of important functional material over the past few decades, showing abundant physical properties such as negative thermal expansion and superconductivity, etc. However, antiperovskite ferroelectrics have scarcely been discovered in inorganic ceramics. In this article, we report a new organic-inorganic hybrid antiperovskite ferroelectric (CH)(F-CHCH)NH(CdCl) based on the strategy of molecular design. The replacement of one methyl in [(CH)NH]CdCl with ethyl produces the lower symmetric [(CH)(CHCH)NH]CdCl with nonpolar perovskite structure, while the polar hexagonal antiperovskite structure with the formula of XBA (where X = [(CH)(F-CHCH)NH], B = [CdCl], and A = [CdCl]) was received after further fluoridation of the ethyl group. Therefore, fluoridation successfully achieves the structural transformation from perovskite to antiperovskite, as well as the significant changes in physical properties from nonferroelectric to ferroelectric. The antiperovskite (CH)(F-CHCH)NH(CdCl) exhibits typical ferroelectric phase transition above room temperature ( T = 333 K) including thermal anomalies, dielectric transitions, and second harmonic generation (SHG) responses. Moreover, lower coercive fields and easy polarization switching are observed by the measurements of hysteresis loops and ferroelectric domains. The saturated polarization ( P) of 4.0 μC/cm is almost 10 times as large as those recently discovered antiperovskite molecular ferroelectrics. This finding provides a novel strategy to design and explore more antiperovskite organic-inorganic hybrid ferroelectric materials.
在过去几十年里，反钙钛矿已发展成为一种重要的功能材料，展现出诸如负热膨胀和超导性等丰富的物理性质。然而，在无机陶瓷中几乎未发现反钙钛矿铁电体。在本文中，我们基于分子设计策略报道了一种新型有机 - 无机杂化反钙钛矿铁电体(CH)(F - CHCH)NH(CdCl)。用乙基取代[(CH)NH]CdCl中的一个甲基会产生具有非极性钙钛矿结构的对称性较低的[(CH)(CHCH)NH]CdCl，而在乙基进一步氟化后得到了化学式为XBA（其中X = [(CH)(F - CHCH)NH]，B = [CdCl]，A = [CdCl]）的极性六方反钙钛矿结构。因此，氟化成功实现了从钙钛矿到反钙钛矿的结构转变，以及从非铁电到铁电的物理性质的显著变化。反钙钛矿(CH)(F - CHCH)NH(CdCl)在室温以上（T = 333 K）表现出典型的铁电相变，包括热异常、介电转变和二次谐波产生（SHG）响应。此外，通过滞后回线和铁电畴的测量观察到较低的矫顽场和容易的极化切换。4.0 μC/cm的饱和极化（P）几乎是最近发现的反钙钛矿分子铁电体的10倍。这一发现为设计和探索更多反钙钛矿有机 - 无机杂化铁电材料提供了一种新策略。
