Octahedral Twisting-Mediated van der Waals Stacking Induces Ultralow Thermal Conductivity.
basic_science · Level V
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- Record sourced from PubMed, PMID 40974135.
- Also identified by DOI 10.1002/adma.202512801.
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Abstract
Low thermal conductivity (κ) is an important physical parameter inherent to all solids, and the quest for intrinsic ultralow-κ solids is one of the key scientific issues. Material design based on functional units can achieve control over lattice and phonon dynamics, and it is proposed that asymmetric structural units-mediated van der Waals stacking can collectively lead to the low thermal conductivity. Herein, a novel van der Waals material In<sub>2</sub>G<sub>2</sub>Se₆ is reported, in which the distorted InSe₆ octahedron forms monolayers in conjunction with Ge<sub>2</sub>Se₆ dimers, which are further stacked along the c-axis via weak metavalent bonding. The distorted octahedron and van der Waals stacking result in large anharmonicity and ultrasoft acoustic phonon along Γ-Z direction, respectively. Consequently, In<sub>2</sub>Ge<sub>2</sub>Se<sub>6</sub> exhibits ultralow out-of-plane thermal conductivity, κ<sub>out-of-plane</sub> ≈0.2 W m<sup>-1</sup>K<sup>-1</sup> at 600 K. This study establishes a model for phonon physics that simultaneously enhances phonon-phonon scattering and lowers the phonon group velocity, revealing the great potential of functional-unit-based material design for low-κ solids.