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arXiv · 2511.11443

Metavalent Bonding-Induced Phonon Hardening and Giant Anharmonicity in BeO

Xuejie Li·Yuzhou Hao·Yujie Liu·Shengying Yue·Xiaolong Yang·Turab Lookman·Xiangdong Ding·Jun Sun·Zhibin Gao
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Abstract

The search for materials with intrinsically low thermal conductivity ($\kappa_L$) is critical for energy applications, yet conventional descriptors often fail to capture the complex interplay between bonding and lattice dynamics. Here, first-principles calculations are used to contrast the thermal transport in covalent zincblende (zb) and metavalent rocksalt (rs) BeO. We find that the metavalent bonding in rs-BeO enhances lattice anharmonicity, activating multi-phonon scattering channels and suppressing phonon transport. This results in an ultralow $\kappa_L$ of 24 W m$^{-1}$ K$^{-1}$ at 300 K, starkly contrasting with the zb phase (357 W m$^{-1}$ K$^{-1}$). Accurately modeling such strongly anharmonic systems requires explicit inclusion of temperature-dependent phonon renormalization and four-phonon scattering. These contributions, negligible in zb-BeO, are essential for high-precision calculations of the severely suppressed $\kappa_L$ in rs-BeO. Finally, we identify three key indicators to guide the discovery of metavalently bonded, incipient-metallic materials: (i) an NaCl-type crystal structure, (ii) large Gr\"uneisen parameters ($\textgreater$2), and (iii) a breakdown of the Lyddane-Sachs-Teller relation. These findings provide microscopic insight into thermal transport suppression by metavalent bonding and offer a predictive framework for identifying promising thermoelectrics and phase-change materials.

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Xuejie Li, Yuzhou Hao, Yujie Liu, Shengying Yue, Xiaolong Yang, Turab Lookman, Xiangdong Ding, Jun Sun, Zhibin Gao. 2025-11-14. Metavalent Bonding-Induced Phonon Hardening and Giant Anharmonicity in BeO. https://arxiv.org/abs/2511.11443

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