Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal, and cubic phases of methylammonium lead iodide
Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal, and cubic phases of methylammonium lead iodide
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DOI：
10.1103/physrevb.92.144308
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发表时间：
2015-10-16
影响因子：
3.7
通讯作者：
Walsh, Aron
中科院分区：
文献类型：
--
作者：
Brivio, Federico;Frost, Jarvist M.;Walsh, Aron
混合卤化物钙钛矿CH 3 NH3 PbI 3表现出复杂的结构行为，在165和327 K附近具有正交晶、四方晶和立方晶型之间的连续转变。在这里，我们报告的第一性原理晶格动力学（声子谱）为每个阶段的CH 3 NH3 PbI 3。的平衡结构比较以及随温度变化的粉末中子衍射的解决方案。通过遵循正常模式，我们计算振动的红外和拉曼强度，并将它们与单晶的测量进行比较，其中控制拉曼激光以避免样品的劣化。尽管与无机（PbI 3-）（n）网络相关的低频模式和有机CH 3 NH3+阳离子的高频模式之间的能量存在明显的分离，但它们之间存在显著的耦合，这强调了结构转变中分子取向和角共享八面体网络之间的相互作用。软模式被发现在边界处的布里渊区的立方相，与位移不稳定性和非谐性涉及倾斜的PbI 6八面体在室温下。
The hybrid halide perovskite CH3NH3PbI3 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 CH3NH3PbI3. 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 (PbI3-)(n) network and high-frequency modes of the organic CH3NH3+ 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 PbI6 octahedra around room temperature.