2D hybrid organic–inorganic halide perovskites emerge as a new class of 2D semiconductors with the potential to combine excellent optoelectronic properties with symmetry-enabled properties such as ferroelectricity. Although many lead-based ferroelectric 2D halide perovskites are reported, there is yet to be a conclusive report of ferroelectricity in tin-based 2D perovskites. Here, the structures and properties of a new series of 2D Dion–Jacobson (DJ) Sn perovskites: (4AMP)SnI₄, (4AMP)(MA)Sn₂I₇, and (4AMP)(FA)Sn₂I₇ (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium, and FA = formamidinium), are reported. Structural characterization reveals that (4AMP)SnI₄ is polar with in-plane spontaneous polarization whereas (4AMP)(MA)Sn₂I₇ and (4AMP)(FA)Sn₂I₇ are centrosymmetric. Further, (4AMP)SnI₄ displays second harmonic generation (SHG) and polarization-electric field hysteresis measurements confirm it is ferroelectric with a spontaneous polarization of 10.0 µC cm⁻² at room temperature. (4AMP)SnI₄ transitions into a centrosymmetric structure above 367 K. As the first direct experimental observation of the spontaneous ferroelectric polarization of a Sn-based 2D hybrid perovskite, this work opens up environmentally friendly 2D tin halide perovskites for ferroelectricity and other physical property studies.

中文翻译：

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无铅铁电二维迪翁-雅各布森碘化锡钙钛矿

二维杂化有机-无机卤化物钙钛矿作为一种新型二维半导体出现，具有将优异的光电特性与铁电性等对称特性结合起来的潜力。尽管报道了许多铅基铁电二维卤化物钙钛矿，但目前尚未有关于锡基二维钙钛矿铁电性的结论性报告。这里介绍了一系列新的 2D Dion-Jacobson (DJ) Sn 钙钛矿的结构和性质：(4AMP)SnI ₄、(4AMP)(MA)Sn ₂ I ₇和 (4AMP)(FA)Sn ₂ I ₇ (据报道，4AMP = 4-(氨基甲基)哌啶鎓、MA = 甲基铵、FA = 甲脒鎓。结构表征表明(4AMP)SnI ₄具有面内自发极化极性，而(4AMP)(MA)Sn ₂ I ₇和(4AMP)(FA)Sn ₂ I ₇是中心对称的。此外，(4AMP)SnI ₄显示二次谐波产生(SHG)，极化电场磁滞测量证实它是铁电体，在室温下自发极化为10.0 µC cm ^-2 。 (4AMP)SnI ₄在367 K以上转变为中心对称结构。作为对Sn基二维杂化钙钛矿自发铁电极化的首次直接实验观察，这项工作开辟了环境友好的二维卤化锡钙钛矿的铁电性和其他物理性质学习。