Intrinsically ultralow thermal conductivity in all-inorganic superatomic bulk crystals

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Abstract
Superatomic compounds, composed of atomic clusters interwoven by weak chemical bonds exhibit large anharmonicity vibrations, are excellent candidates for ultralow thermal conductivity (κ) materials. However, growing bulk superatomic single crystals is challenging due to complex chemical composition and chemical bonds, and studies on their intrinsic thermal property are scarce. Here, we grew high-quality superatomic single crystals of Re6Se8Te7 and Re6Te15, both of which are narrow-bandgap semiconductors that change into metals under external physical pressure. At room temperature, κ is 0.32 ± 0.02 and 0.53 ± 0.02 W m−1 K−1 in Re6Se8Te7 and Re6Te15, respectively, ranking among the lowest values reported in all-inorganic bulk crystals. It is mainly attributed to the large Grüneisen parameter (1.93) and low average sound speed (<1482 m/s), which are due to soft Te7 nets weakly embedded among the rigid Re6Se8 (Re6Te8) quasi-cubic clusters. The appearance of boson peak, i.e., a hump of C(T)/T3, verifies the existence of disordered phonon transports. In addition, the temperature dependence of κ can be described by the classic Debye–Callaway model. Notably, above 350 K, the κ values of Re6Se8Te7 and Re6Te15 are remarkably close to the upper limit derived from a glassy-like diffusion model. This finding sets the superatomic compounds as a promising family for searching ultralow-κ and energy management materials.
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Funding Information
  • National Natural Science Foundation of China (52250308)
  • National Natural Science Foundation of China (52521007)
  • National Key Research and Development Program of China (2023YFA1406301)
  • National Key Research and Development Program of China (2024YFA1207900)
  • National Natural Science Foundation of China (52202342)
  • National Natural Science Foundation of China (12374012)
  • Natural Science Foundation of Shandong Province (ZR2023JQ001)
  • National Natural Science Foundation of China (52525205)
  • Synergetic Extreme Condition User Facility (CSTR:31123.02.SECUF)
  • Scientific Research Innovation Capability Support Project for Young Faculty (ZYGXQNJSKYCXNLZCXM-E1)
  • Beijing Natural Science Foundation (1254054)

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