Intrinsic ultralow lattice thermal conductivity in lead-free halide perovskites Cs 3 Bi 2 X 9 (X = Br, I)

Lead-free halide perovskites have recently garnered significant attention due to their rich structural diversity and exceptionally ultralow lattice thermal conductivity ( ). Here, we employ first-principles calculations in conjunction with self-consistent phonon theory and Boltzmann transport equati...

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Published in:Physical chemistry chemical physics : PCCP 2024-08, Vol.26 (32), p.21801-21809
Main Authors: Ma, Jiang-Jiang, Zheng, Jing-Jing, Chen, Yuxi, Ren, Qingyong, Zhang, Junfeng, Wang, Bao-Tian
Format: Article
Language:English
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Summary:Lead-free halide perovskites have recently garnered significant attention due to their rich structural diversity and exceptionally ultralow lattice thermal conductivity ( ). Here, we employ first-principles calculations in conjunction with self-consistent phonon theory and Boltzmann transport equations to investigate the crystal structure, electronic structure, mechanical properties, and s of two typical vacancy-ordered halide perovskites, denoted with the general formula Cs Bi X (X = Br, I). Ultralow s of 0.401 and 0.262 W mK at 300 K are predicted for Cs Bi Br and Cs Bi I , respectively. Our findings reveal that the ultralow s are mainly associated with the Cs rattling-like motion, vibrations of halide polyhedral frameworks, and strong scattering in the acoustic and low-frequency optical phonon branches. The structural analysis indicates that these phonon dynamic properties are closely relevant to the bonding hierarchy. The presence of the extended Bi-X antibonding states at the valence band maximum contributes to the soft elastic lattice and low phonon group velocities. Compared to Cs Bi Br , the face-sharing feature and weaker bond strength in Cs Bi I lead to a softer elasticity modulus and stronger anharmonicity. Additionally, we demonstrate the presence of wave-like in Cs Bi X by evaluating the coherent contribution. Our work provides the physical microscopic mechanisms of the wave-like in two typical lead-free halide perovskites, which are beneficial to designing intrinsic materials with the feature of ultralow .
ISSN:1463-9076
1463-9084
DOI:10.1039/D4CP02005G