Vibrational hierarchy leads to dual-phonon transport in low thermal conductivity crystals

Yixiu Luo, Xiaolong Yang, Tianli Feng, Jingyang Wang and Xiulin Ruan ()
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Yixiu Luo: Purdue University
Xiaolong Yang: Purdue University
Tianli Feng: Energy and Transportation Science Division, Oak Ridge National Laboratory
Jingyang Wang: Chinese Academy of Sciences
Xiulin Ruan: Purdue University

Nature Communications, 2020, vol. 11, issue 1, 1-10

Abstract: Abstract Many low-thermal-conductivity (κL) crystals show intriguing temperature (T) dependence of κL: κL ∝ T−1 (crystal-like) at intermediate temperatures whereas weak T-dependence (glass-like) at high temperatures. It has been in debate whether thermal transport can still be described by phonons at the Ioffe-Regel limit. In this work, we propose that most phonons are still well defined for thermal transport, whereas they carry heat via dual channels: normal phonons described by the Boltzmann transport equation theory, and diffuson-like phonons described by the diffusion theory. Three physics-based criteria are incorporated into first-principles calculations to judge mode-by-mode between the two phonon channels. Case studies on La2Zr2O7 and Tl3VSe4 show that normal phonons dominate low temperatures while diffuson-like phonons dominate high temperatures. Our present dual-phonon theory enlightens the physics of hierarchical phonon transport as approaching the Ioffe-Regel limit and provides a numerical method that should be practically applicable to many materials with vibrational hierarchy.

Date: 2020
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DOI: 10.1038/s41467-020-16371-w

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