正交晶系
非谐性
四方晶系
八面体
拉曼光谱
结晶学
材料科学
分子振动
软模式
格子(音乐)
晶体结构
中子衍射
立方晶系
声子
凝聚态物理
物理
化学
铁电性
光学
电介质
光电子学
声学
作者
Federico Brivio,Jarvist M. Frost,Jonathan M. Skelton,Adam J. Jackson,Oliver J. Weber,Mark T. Weller,A. R. Goñi,Aurélien M. A. Leguy,Piers R. F. Barnes,Aron Walsh
出处
期刊:Physical Review B
[American Physical Society]
日期:2015-10-16
卷期号:92 (14)
被引量:470
标识
DOI:10.1103/physrevb.92.144308
摘要
The hybrid halide perovskite ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$ exhibits a complex structural behavior, with successive transitions between orthorhombic, tetragonal, and cubic polymorphs around 165 and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$. The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes, we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of the sample. Despite a clear separation in energy between low-frequency modes associated with the inorganic (${\mathrm{PbI}}_{3}{}^{\ensuremath{-}}{)}_{n}$ network and high-frequency modes of the organic ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{}^{+}$ cation, significant coupling between them is found, which emphasizes the interplay between molecular orientation and the corner-sharing octahedral networks in the structural transformations. Soft modes are found at the boundary of the Brillouin zone of the cubic phase, consistent with displacive instabilities and anharmonicity involving tilting of the ${\mathrm{PbI}}_{6}$ octahedra around room temperature.
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