论文标题
ch $ _ {3} $ nh $ _ {3} $ pbi $ _ {3} $的四方阶段是强烈的anharmonic
The tetragonal phase of CH$_{3}$NH$_{3}$PbI$_{3}$ is strongly anharmonic
论文作者
论文摘要
卤化物钙钛矿（HP）半导体在电子和结构动力学之间表现出独特的强耦合。已知HPS的高温立方相被熵稳定，并在计算出的声子分散关系中具有假想频率。基于静态平均晶体结构的类似计算，预测没有假想模式的稳定四方相。这项工作表明，与标准理论预测相比，ch $ _ {3} $ nh $ _ {3} $ pbi $ _ {3} $的室温四方阶段是强烈的。我们使用拉曼极化取向（PO）测量值和\ textIt {ab intio}分子动力学（AIMD）来研究整个四方阶段强结构非谐度的起源和温度演化。拉曼PO测量揭示了类似于软模式的新光谱功能。这种模式显示了与温度的阻尼不寻常的持续增加，这表明了非谐电势表面。对AIMD轨迹的分析确定了两个主要来源：[Ch $ _ {3} $ nh $ _ {3} $ _ {3} $] $^+$ ions的定向解锁和大幅度八面体倾斜，随着温度不断升高。我们的工作表明，标准声子图片无法描述四方ch $ _ {3} $ nh $ _ {3} $ pbi $ _ {3} $的结构动力学。
Halide perovskite (HP) semiconductors exhibit unique strong coupling between the electronic and structural dynamics. The high-temperature cubic phase of HPs is known to be entropically stabilized, with imaginary frequencies in the calculated phonon dispersion relation. Similar calculations, based on the static average crystal structure, predict a stable tetragonal phase with no imaginary modes. This work shows that in contrast to standard theory predictions, the room-temperature tetragonal phase of CH$_{3} $NH$_{3} $PbI$_{3}$ is strongly anharmonic. We use Raman polarization-orientation (PO) measurements and \textit{ab initio} molecular dynamics (AIMD) to investigate the origin and temperature evolution of the strong structural anharmonicity throughout the tetragonal phase. Raman PO measurements reveal a new spectral feature that resembles a soft mode. This mode shows an unusual continuous increase in damping with temperature which is indicative of an anharmonic potential surface. The analysis of AIMD trajectories identifies two major sources of anharmonicity: the orientational unlocking of the [CH$_{3} $NH$_{3}$]$^+$ ions and large amplitude octahedral tilting that continuously increases with temperature. Our work suggests that the standard phonon picture cannot describe the structural dynamics of tetragonal CH$_{3} $NH$_{3} $PbI$_{3}$.
