Optical-Phonon-Enabled Large Lattice Thermal Conductivity Anisotropy in Hexagonal Perovskites CsBX3 (B = Mg, Cd; X = Cl, Br, I)
Abstract
Materials exhibiting strongly anisotropic lattice thermal conductivity are desirable for thermal-management applications, yet such behavior is commonly associated with layered or quasi-one-dimensional van der Waals crystals and highly anisotropic elastic properties. Here, we investigate lattice thermal transport in the hexagonal perovskites CsBX3 (B= Mg, Cd; X= Cl, Br, I) using first-principles calculations. At 300~K, the calculated in-plane and out-of-plane lattice thermal conductivities range from 0.13--0.83 and 0.34--6.26~Wm−1K−1, respectively, corresponding to anisotropy ratios of 2.6--7.5. This pronounced anisotropy is remarkable given the relatively modest elastic anisotropy, characterized by C33/C11 = 0.994--1.842. Our analysis reveals that medium-frequency optical phonons provide an efficient out-of-plane heat-transport channel, contrary to the conventional picture in which heat transport is dominated by acoustic phonons. These findings identify face-sharing octahedral frameworks as a promising platform for engineering strong thermal-conductivity anisotropy in mechanically near-isotropic, non--van der Waals crystals.
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BibTeX
@misc{cao2026opticalphononenabled,
title = {{Optical-Phonon-Enabled Large Lattice Thermal Conductivity Anisotropy in Hexagonal Perovskites Cs$BX_3$ ($B$ = Mg, Cd; $X$ = Cl, Br, I)}},
author = {Lingzhi Cao and Ying Song and Zhonghao Xia and Jianye Liu and Jiangang He},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.00512},
eprint = {2609.00512},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.00512},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Optical-Phonon-Enabled Large Lattice Thermal Conductivity Anisotropy in Hexagonal Perovskites CsBX_3 (B = Mg, Cd; X = Cl, Br, I)
AU - Lingzhi Cao
AU - Ying Song
AU - Zhonghao Xia
AU - Jianye Liu
AU - Jiangang He
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.00512
UR - https://arxiv.org/abs/2609.00512
AB - Materials exhibiting strongly anisotropic lattice thermal conductivity are desirable for thermal-management applications, yet such behavior is commonly associated with layered or quasi-one-dimensional van der Waals crystals and highly anisotropic elastic properties. Here, we investigate lattice thermal transport in the hexagonal perovskites CsBX_3 (B= Mg, Cd; X= Cl, Br, I) using first-principles calculations. At 300~K, the calculated in-plane and out-of-plane lattice thermal conductivities range from 0.13--0.83 and 0.34--6.26~Wm^−1K^−1, respectively, corresponding to anisotropy ratios of 2.6--7.5. This pronounced anisotropy is remarkable given the relatively modest elastic anisotropy, characterized by C_33/C_11 = 0.994--1.842. Our analysis reveals that medium-frequency optical phonons provide an efficient out-of-plane heat-transport channel, contrary to the conventional picture in which heat transport is dominated by acoustic phonons. These findings identify face-sharing octahedral frameworks as a promising platform for engineering strong thermal-conductivity anisotropy in mechanically near-isotropic, non--van der Waals crystals.
ER -