Abstract
Phonon-related behaviors such as hot-carrier bottleneck and thermooptic coefficients stimulate the study of lattice dynamics and thermal conductivity () in perovskites. Herein, we report ultralow thermal conductivities of synthesized highly oriented samples of ( 0.45 W/mK at 300 K) and ( 0.60 W/mK at 300 K). Phonon frequency renormalization of the octahedral rotational soft modes in triggered by the fourth-order anharmonicity considerably amends the three- and four-phonon linewidths, significantly altering the thermal transport property of . Furthermore, the phonon gas model partially breaks down, and both normal and diffuson-like phonons must be considered to capture the nearly temperature-independent of . We also find these unusual phonon behaviors in other layered inorganic perovskites such as and . Our results rationalize the crucial high-order phonon interactions and two-channel lattice thermal transports in perovskites with ultralow .
- Received 15 September 2021
- Revised 22 December 2021
- Accepted 27 April 2022
DOI:https://doi.org/10.1103/PhysRevB.105.184303
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