Yang Yali, Lou Feng, Xiang Hongjun
Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.
Shanghai Qizhi Institution, Shanghai 200232, People's Republic of China.
Nano Lett. 2021 Apr 14;21(7):3170-3176. doi: 10.1021/acs.nanolett.1c00395. Epub 2021 Mar 23.
Two-dimensional (2D) ferroelectric (FE) hybrid organic-inorganic perovskites (HOIPs) are promising for potential applications as miniaturized flexible ferroelectric/piezoelectric devices. Recently, several 2D HOIPs [e.g., Ruddlensden-Popper type HOIP BAPbCl (BA = CHCHNH)] were reported to possess room-temperature ferroelectricity. However, the underlying microscopic mechanisms for ferroelectricity in 2D HOIPs remain elusive. Here, by performing first-principles calculations and symmetry mode analysis, we demonstrate that there exists a cooperative coupling between A-site organic molecules and B-site inorganic Pb ions that is essential to the ferroelectricity in 2D BAPbCl. The nonpolar ground state of the closely related compounds BAPbBr and BAPbI can also be explained in terms of the weakened cooperative coupling. We further predict that 2D BAPbF displays in-plane ferroelectricity with a higher Curie temperature and larger electric polarization. Our work not only reveals the unusual FE mechanism in 2D HOIPs but also provides a solid theoretical basis for the rational design of 2D multifunctional materials.
二维（2D）铁电（FE）有机-无机杂化钙钛矿（HOIPs）在作为小型化柔性铁电/压电器件的潜在应用方面很有前景。最近，有报道称几种二维HOIPs [例如，Ruddlensden-Popper型HOIP BAPbCl（BA = CHCHNH）]具有室温铁电性。然而，二维HOIPs中铁电性的潜在微观机制仍然难以捉摸。在这里，通过进行第一性原理计算和对称模式分析，我们证明了A位有机分子和B位无机Pb离子之间存在协同耦合，这对于二维BAPbCl中的铁电性至关重要。密切相关的化合物BAPbBr和BAPbI的非极性基态也可以用减弱的协同耦合来解释。我们进一步预测二维BAPbF表现出具有更高居里温度和更大极化强度的面内铁电性。我们的工作不仅揭示了二维HOIPs中不寻常的铁电机制，而且为二维多功能材料的合理设计提供了坚实的理论基础。
