Effect of static local distortions vs. dynamic motions on the stability and band gaps of cubic oxide and halide perovskites
Effect of static local distortions vs. dynamic motions on the stability and band gaps of cubic oxide and halide perovskites
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DOI：
10.1016/j.mattod.2021.05.021
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发表时间：
2021-04
期刊：
影响因子：
24.2
通讯作者：
Xingang Zhao;Zhi Wang;O. Malyi;A. Zunger
中科院分区：
文献类型：
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作者：
Xingang Zhao;Zhi Wang;O. Malyi;A. Zunger
由共享角的 BX6 八面体制成的三元 ABX3 钙钛矿长期以来在固态化学和凝聚态物理中占有重要地位。尽管如此，对它们的两个主要亚组——卤化物和氧化物——的共同理解尚未得到充分发展。事实上，与具有单一、稳健的重复基序（“单形”）的更简单化合物的情况不同，某些立方钙钛矿可以表现出局部基序的非热（=固有）分布（“多形网络”）。这种静态变形可以包括顺磁体中的位置自由度（例如，原子位移和八面体倾斜）或磁矩自由度。与热运动不同，这种静态变形不会在时间上平均为零，这是化学键的内在对称性破坏偏好的表达。本研究比较了氧化物和卤化物钙钛矿的电子结构特征，从密度泛函理论（DFT）内能最小化描述的基序的静态多态分布开始，继续通过有限温度DFT分子动力学建模的有限温度热无序。我们发现 (i) 不同的氧化物与卤化物 ABX3 化合物采用不同的能量降低对称性破缺模式。根据第一原理计算出的 SrTiO3 对分布函数 (PDF) 与最近测量的 PDF 一致。 (ii) 在氧化物和卤化物中，这种静态畸变会导致相对于未畸变立方 Pm-3m 结构的带隙蓝移。 （iii）对于氧化物钙钛矿，从静态扭曲的多晶型结构引发的高温分子动力学模拟表明，热引起的扭曲可以导致带隙红移。 (iv) 相反，对于立方卤化物钙钛矿 CsPbI3，本征畸变和热畸变共同导致带隙蓝移，前者的本征效应占主导地位。 (v) 在氧化物 SrTiO3 和 CaTiO3（但不在卤化物中）钙钛矿中，八面体倾斜导致出现明显的 Г-Г 直接带隙分量，作为众所周知的间接 R-Г 带隙的次要谷最小值。了解氧化物与卤化物钙钛矿的这种本征效应与热效应具有设计目标电子特性的潜力。
Ternary ABX3perovskites made of corner-sharing BX6octahedra have long featured prominently in solid-state chemistry and condensed matter physics. Still, the joint understanding of their two main subgroups—halidesandoxides—has not been fully developed. Indeed, unlike the case in simpler compounds having a single, robust repeated motif (“monomorphous”), certain cubic perovskites can manifest a non-thermal (= intrinsic) distribution of local motifs (“polymorphous networks”). Such static deformations can include positional degrees of freedom (e.g., atomic displacements and octahedral tilting) or magnetic moment degrees of freedom in paramagnets. Unlike thermal motion, such static distortions do not time-average to zero, being an expression of the intrinsic symmetry breaking preference of the chemical bonding. The present study compares electronic structure features of oxide and halide perovskites starting from the static polymorphous distribution of motifs described by Density Functional Theory (DFT) minimization of the internal energy, continuing to finite temperature thermal disorder modeled via finite temperature DFT molecular dynamics. We find that (i) differentoxide vs. halideABX3compounds adopt different energy-lowering symmetry-breaking modes. The calculated pair distribution function (PDF) of SrTiO3from the first-principles agrees with recently measured PDF. (ii) In both oxides and halides, such static distortions lead to band gapblueshiftswith respect to undistorted cubicPm-3mstructure. (iii) For oxide perovskites, high-temperature molecular dynamics simulations initiated from the statically distorted polymorphous structures reveal that thethermally-induceddistortions can lead to a band gapredshift. (iv) In contrast, for cubichalideperovskite CsPbI3, both the intrinsic distortions and the thermal distortions contribute in tandem to band gapblueshift, the former, intrinsic effect being dominant. (v) In the oxide SrTiO3and CaTiO3(but not in halide) perovskites, octahedral tilting leads to the emergence of a distinct Γ–Γ direct band gap component as a secondary valley minimum to the well-known indirect R–Γ gap. Understanding such intrinsic vs. thermal effects onoxide vs. halideperovskites holds the potential for designing target electronic properties.