Caicedo-Dávila Sebastián, Cohen Adi, Motti Silvia G, Isobe Masahiko, McCall Kyle M, Grumet Manuel, Kovalenko Maksym V, Yaffe Omer, Herz Laura M, Fabini Douglas H, Egger David A
Physics Department, TUM School of Natural Sciences, Technical University of Munich, Garching, Germany.
Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot, Israel.
Nat Commun. 2024 May 17;15(1):4184. doi: 10.1038/s41467-024-48581-x.
Halide perovskites show great optoelectronic performance, but their favorable properties are paired with unusually strong anharmonicity. It was proposed that this combination derives from the ns electron configuration of octahedral cations and associated pseudo-Jahn-Teller effect. We show that such cations are not a prerequisite for the strong anharmonicity and low-energy lattice dynamics encountered in these materials. We combine X-ray diffraction, infrared and Raman spectroscopies, and molecular dynamics to contrast the lattice dynamics of CsSrBr with those of CsPbBr, two compounds that are structurally similar but with the former lacking ns cations with the propensity to form electron lone pairs. We exploit low-frequency diffusive Raman scattering, nominally symmetry-forbidden in the cubic phase, as a fingerprint of anharmonicity and reveal that low-frequency tilting occurs irrespective of octahedral cation electron configuration. This highlights the role of structure in perovskite lattice dynamics, providing design rules for the emerging class of soft perovskite semiconductors.
卤化物钙钛矿表现出优异的光电性能，但其良好的性能伴随着异常强的非谐性。有人提出，这种组合源于八面体阳离子的ns电子构型和相关的赝 Jahn-Teller 效应。我们表明，这种阳离子并非这些材料中强非谐性和低能晶格动力学的先决条件。我们结合 X 射线衍射、红外和拉曼光谱以及分子动力学，对比 CsSrBr 和 CsPbBr 的晶格动力学，这两种化合物结构相似，但前者缺乏有形成电子孤对倾向的 ns 阳离子。我们利用低频扩散拉曼散射（在立方相中名义上是对称禁戒的）作为非谐性的指纹，揭示低频倾斜的发生与八面体阳离子的电子构型无关。这突出了结构在钙钛矿晶格动力学中的作用，为新兴的软钙钛矿半导体类提供了设计规则。
