Unravelling ultralow thermal conductivity in perovskite Cs₂AgBiBr₆: dominant wave-like phonon tunnelling and strong anharmonicity 

Jiongzhi Zheng, Changpeng Lin, Chongjia Lin, Geoffroy Hautier, Ruiqiang Guo & Baoling Huang 

npj Computational Materials 10: 30 (2024); Published online: 06 February 2024

Editorial Summary

Wave-like phonon tunnelling: Failure of the phonon gas model in lead-free halide double perovskites

In recent years, lead-free halide double perovskites have gained a lot of attention in the field of solar energy due to their environmental friendliness and stability. Additionally, their potential for extremely low thermal conductivity has sparked interest in the field of thermoelectrics. However, their strong temperature-dependent thermal properties make traditional lattice dynamics and heat transfer prediction models ineffective. This study introduces a heat transfer prediction model that integrates multiple factors. This model not only accurately considers the influence of finite temperatures on the thermal properties of double perovskite materials but also adds extra heat transfer pathways beyond traditional models. This allows for precise predictions and revelations about the heat transfer mechanisms of lead-free halide double perovskites. The research team, led by Professor Huang Baoling from the Department of Mechanical and Aerospace Engineering at the Hong Kong University of Science and Technology, Professor Guo Ruiqiang's team from the Shandong Advanced Academy, and Professor Geoffroy Hautier's team from Dartmouth College in the United States, comprehensively considered the effects of multi-phonon temperature, additional phonon heat transfer pathways, and four-phonon interaction processes. This revealed the heat transfer mechanisms of lead-free halide double perovskite Cs2AgBiBr6 and identified new additional phonon transfer pathways that dominate the heat transfer process. Apart from accurately revealing the heat transfer mechanisms of lead-free halide double perovskite Cs2AgBiBr6, the study also accurately predicted the phase transition temperature of double perovskite Cs2AgBiBr6. It emphasized the importance of three-phonon particle interactions for accurate phase transition temperature predictions. Additionally, considering the strong temperature dependence of double perovskites, four-phonon particle interactions are indispensable, and their involvement renders traditional heat transfer models ineffective. The research underscores the significance of lattice anharmonicity (temperature effects) and phonon wave-like tunnelling heat transfer pathways in the thermal transfer mechanism of lead-free halide double perovskite Cs2AgBiBr6.

编辑概述

类波性声子隧穿：无铅卤化物双钙钛矿中声子气模型失效

近年来，无铅卤化物双钙钛矿由于其环境友好性以及稳定性， 在光电光伏领域得到了极大的关注。同时，由于其强非简谐性可能引起超低热导率，该材料在热电领域也引起了极大的关注。然而，无铅卤化物双钙钛矿的热力学性质具有强烈的温度依赖性，导致传统的晶格动力学和导热模型难以适用。为解决该问题，香港科技大学机械与航天航空工程系黄宝陵教授团队，山东高等技术研究院郭瑞强教授团队以及美国达特茅斯学院Geoffroy Hautier 教授团队合作，提出了一种综合考虑多种因素的导热模型，该模型不仅精确考虑了有限温度对材料热力学性能的影响，而且在传统导热模型的基础上增加了额外的导热通道，从而能够精准预测无铅卤化物双钙钛矿的热导率，揭示其导热机理。该研究通过综合考虑多声子温度效应，额外声子热传输通道以及四声子相互作用揭示了Cs₂AgBiBr₆的导热机理，发现了类波性声子隧穿在其导热过程中的主导作用。该研究不仅揭示了无铅卤化物双钙钛矿Cs₂AgBiBr₆的导热机理，还准确预测了其相变温度，发现了三声子相互作用对准确预测相变温度的重要性。此外，鉴于双钙钛矿热力学性质的强温度依赖性，四声子相互作用成为了一个关键因素，其纳入考量导致了传统导热模型的失效。该研究揭示了晶格的非简谐性和类波性声子隧穿对无铅卤化物双钙钛矿热输运的重要影响。