Finite-temperature simulation of anharmonicity and octahedral tilting transitions in halide perovskites
Finite-temperature simulation of anharmonicity and octahedral tilting transitions in halide perovskites
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DOI：
10.1103/physrevmaterials.3.113605
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发表时间：
2019-11-18
影响因子：
3.4
通讯作者：
Van der Ven, Anton
中科院分区：
文献类型：
--
作者：
Bechtel, Jonathon S.;Thomas, John C.;Van der Ven, Anton
在大多数无机卤化物钙钛矿中观察到八面体倾斜转变，并在决定其功能和热力学性质方面起着重要作用。尽管在室温附近存在，但立方和四方的卤化物钙钛矿在低温下变得动态不稳定，这使得用常用的准谐模型来研究其热力学性质是不可能的。构造了一个非简谐振动哈密顿量，它准确地再现了卤化物钙钛矿CsPbBr3势能面的低能部分。用密度泛函理论计算的CsPbBr3晶体大幅度形变的能量的大的第一原理数据集验证了哈密顿量。对哈密顿量进行的蒙特卡罗模拟重现了在CsPbBr3和许多其他卤化物钙钛矿中观察到的正交-四方-立方相变，证明了非简谐振动激发对稳定这些材料中的四方相和立方相的重要性。从蒙特卡罗模拟获得的立方相和四方相的局部结构和八面体倾斜的测量结果证实了实验观察到的大的各向异性位移因子与八面体倾斜之间的联系。
Octahedral tilting transitions are observed in most inorganic halide perovskites and play an important role in determining their functional and thermodynamic properties. Despite existing near room temperature, the cubic and tetragonal forms of halide perovskites become dynamically unstable at low temperature, making it impossible to study their thermodynamic properties with commonly used quasiharmonic models. An anharmonic vibrational Hamiltonian is constructed that accurately reproduces the low-energy portion of the potential-energy surface of the halide perovskite CsPbBr3. The Hamiltonian is validated using a large first-principles dataset of energies calculated within density functional theory for large-amplitude deformations of the CsPbBr3 crystal. Monte Carlo simulations performed on the Hamiltonian reproduce the orthorhombic-tetragonal-cubic phase transitions observed in CsPbBr3 and many other halide perovskites, demonstrating the importance of anharmonic vibrational excitations in stabilizing the tetragonal and cubic phases in these materials. Measures of local structure and octahedral tilting in the cubic and tetragonal phases, obtained from Monte Carlo simulations, confirm the connection between large anisotropic displacement factors and octahedral tilting, as observed experimentally.