Realizing Intrinsically Ultralow and Glass-Like Thermal Transport via Chemical Bonding Engineering.

Area of Science:

• Materials Science
• Solid State Physics
• Thermodynamics

Background:

• Crystals with glass-like, low lattice thermal conductivity (κL) are valuable for thermal barrier coatings, thermoelectric energy conversion, and thermal management.
• Such properties are typically found in compounds with heavy elements, large unit cells, or at high temperatures.

Purpose of the Study:

• To explore chemical bonding principles to weaken Ag-Ag bonds and enhance lattice anharmonicity in Ag6-octahedron-based compounds.
• To design and identify novel compounds with ultralow thermal conductivity through chemical bonding engineering.

Main Methods:

• Utilized chemical bonding principles to weaken Ag-Ag bonds and enhance lattice anharmonicity.
• Incorporated a chalcogen anion as a bridge ligand to facilitate phonon rattling.
• Theoretically identified five Ag6 octahedron-based compounds (AAg3X2, A = Li, Na, K; X = S, Se) with low average atomic masses and strong four-phonon scattering.

Main Results:

• The identified compounds exhibit ultralow thermal conductivities (0.3–0.6 W m⁻¹ K⁻¹) with minimal temperature dependence (T⁻⁰.¹).
• Experimental validation confirmed a κL of 0.45 W m⁻¹ K⁻¹ for NaAg3S2 between 200–550 K.
• Demonstrated strong four-phonon scattering due to weak chemical bonding and low average atomic mass.

Conclusions:

• Weak chemical bonding is crucial for designing materials with glass-like lattice thermal conductivity.
• Chemical bonding engineering is an effective strategy for achieving desired thermal transport properties.
• The identified Ag6 octahedron-based compounds represent promising candidates for advanced thermal management applications.