Professor Yue Chen of the Department of Mechanical Engineering and his team worked on the research for the topic “Pushing thermal conductivity to its lower limit in crystals with simple structures”. The research findings were recently published in Nature Communications on April 8, 2024.
Details of the publication:
Pushing thermal conductivity to its lower limit in crystals with simple struc tures
Zezhu Zeng, Xingchen Shen, Ruihuan Cheng, Olivier Perez, Niuchang Ouyang, Zheyong Fan, Pierric Lemoine, Bernard Raveau, Emmanuel Guilmeau, Yue Chen, article in Nature Communications
Abstract
Materials with low thermal conductivity usually have complex crystal structures. Herein we experimentally find that a simple crystal structure material AgTlI2 (I4/mcm) owns an extremely low thermal conductivity of 0.25 W/mK at room temperature. To understand this anomaly, we perform in-depth theoretical studies based on ab initio molecular dynamics simulations and anharmonic lattice dynamics. We find that the unique atomic arrangement and weak chemical bonding provide a permissive environment for strong oscillations of Ag atoms, leading to a considerable rattling behaviour and giant lattice anharmonicity. This feature is also verified by the experimental probability density function refinement of single-crystal diffraction. The particularly strong anharmonicity breaks down the conventional phonon gas model, giving rise to non-negligible wavelike phonon behaviours in AgTlI2 at 300 K. Intriguingly, unlike many strongly anharmonic materials where a small propagative thermal conductivity is often accompanied by a large diffusive thermal conductivity, we find an unusual coexistence of ultralow propagative and diffusive thermal conductivities in AgTlI2 based on the thermal transport unified theory. This study underscores the potential of simple crystal structures in achieving low thermal conductivity and encourages further experimental research to enrich the family of materials with ultralow thermal conductivity.