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


ABSTRACT: Many low-thermal-conductivity (?L) crystals show intriguing temperature (T) dependence of ?L: ?L???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.

SUBMITTER: Luo Y 

PROVIDER: S-EPMC7244571 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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

Luo Yixiu Y   Yang Xiaolong X   Feng Tianli T   Wang Jingyang J   Ruan Xiulin X  

Nature communications 20200522 1


Many low-thermal-conductivity (κ<sub>L</sub>) crystals show intriguing temperature (T) dependence of κ<sub>L</sub>: κ<sub>L</sub> ∝ T<sup>-1</sup> (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 p  ...[more]

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