Above-room-temperature ferroelectricity in a single-component molecular crystal
Above-room-temperature ferroelectricity in a single-component molecular crystal
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DOI：
10.1038/nature09363
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发表时间：
2010
期刊：
影响因子：
64.8
通讯作者：
S. Horiuchi;Y. Tokunaga;G. Giovannetti;S. Picozzi;H. Itoh;R. Shimano;R. Kumai;Y. Tokura
中科院分区：
文献类型：
--
作者：
S. Horiuchi;Y. Tokunaga;G. Giovannetti;S. Picozzi;H. Itoh;R. Shimano;R. Kumai;Y. Tokura
铁电体是电活性材料，可以存储和切换它们的极性（铁电性），感测温度变化（热电性），交换电和机械功能（压电性），以及操纵光（通过光学非线性和电光效应）：所有这些功能都有实际应用。有机分子中π-共轭的拓扑转换，如酮-烯醇转化，长期以来一直被认为是在分子组装体和晶体中实现这些现象的一种手段。克酮酸是黑色染料的一种成分，最近发现在结晶状态下具有氢键极性结构。在这里，我们证明了电场的应用程序可以连贯地对齐分子的极性在晶体克酮酸，如所示的光学二次谐波产生的增加，并在室温下产生一个明确的极化滞后。为了使这个简单的五边形分子成为铁电体，我们使用同步质子转移而不是刚体旋转来切换π键拓扑。在有机铁电体中，尽管分子尺寸很小，但该分子晶体表现出最高的自发极化（~ 20 μC cm-2），这与第一性原理电子结构计算结果雅阁。这种高偏振，持续高达400 K，可能会发现在未来的有机电子学中的有源电容器和非线性光学元件的应用。
Ferroelectrics are electro-active materials that can store and switch their polarity (ferroelectricity), sense temperature changes (pyroelectricity), interchange electric and mechanical functions (piezoelectricity), and manipulate light (through optical nonlinearities and the electro-optic effect): all of these functions have practical applications. Topological switching of π-conjugation in organic molecules, such as the keto-enol transformation, has long been anticipated as a means of realizing these phenomena in molecular assemblies and crystals. Croconic acid, an ingredient of black dyes, was recently found to have a hydrogen-bonded polar structure in a crystalline state. Here we demonstrate that application of an electric field can coherently align the molecular polarities in crystalline croconic acid, as indicated by an increase of optical second harmonic generation, and produce a well-defined polarization hysteresis at room temperature. To make this simple pentagonal molecule ferroelectric, we switched the π-bond topology using synchronized proton transfer instead of rigid-body rotation. Of the organic ferroelectrics, this molecular crystal exhibits the highest spontaneous polarization (∼20 μC cm-2) in spite of its small molecular size, which is in accord with first-principles electronic-structure calculations. Such high polarization, which persists up to 400 K, may find application in active capacitor and nonlinear optics elements in future organic electronics.