Spontaneous Octahedral Tilting in the Cubic Inorganic Cesium Halide Perovskites CsSnX3 and CsPbX3 (X = F, Cl, Br, I),The Journal of Physical Chemistry Letters

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Spontaneous Octahedral Tilting in the Cubic Inorganic Cesium Halide Perovskites CsSnX3 and CsPbX3 (X = F, Cl, Br, I)
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2017-09-18 00:00:00 , DOI: 10.1021/acs.jpclett.7b02423
Ruo Xi Yang _{1,

2} , Jonathan M. Skelton ₁ , E. Lora da Silva ₁ , Jarvist M. Frost _{1,

2} , Aron Walsh _{2,

3}

Affiliation

The local crystal structures of many perovskite-structured materials deviate from the average space-group symmetry. We demonstrate, from lattice-dynamics calculations based on quantum chemical force constants, that all of the cesium–lead and cesium–tin halide perovskites exhibit vibrational instabilities associated with octahedral titling in their high-temperature cubic phase. Anharmonic double-well potentials are found for zone-boundary phonon modes in all compounds with barriers ranging from 108 to 512 meV. The well depth is correlated with the tolerance factor and the chemistry of the composition, but is not proportional to the imaginary harmonic phonon frequency. We provide quantitative insights into the thermodynamic driving forces and distinguish between dynamic and static disorder based on the potential-energy landscape. A positive band gap deformation (spectral blue shift) accompanies the structural distortion, with implications for understanding the performance of these materials in applications areas including solar cells and light-emitting diodes.

中文翻译：

立方无机卤化铯钙钛矿CsSnX ₃和CsPbX ₃中的自发八面体倾斜（X = F，Cl，Br，I）

许多钙钛矿结构材料的局部晶体结构偏离平均空间群对称性。通过基于量子化学力常数的晶格动力学计算，我们证明了所有铯-铅和铯-锡卤化物钙钛矿在高温立方相中均表现出与八面体滴定相关的振动不稳定性。在势垒范围为108至512 meV的所有化合物中，发现了区域边界声子模的非谐双阱势。井深与公差因子和成分的化学性质相关，但与虚谐波声子频率不成比例。我们提供有关热力学驱动力的定量见解，并根据势能图景区分动态和静态无序。

更新日期：2017-09-18

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