Liquid-like thermal conductivity in the ordered crystal CsAg5Te3

Thermoelectric effect is a phenomenon that utilizes temperature difference to achieve electrical transport, offering potential solutions to the energy and environmental challenges faced by humanity. High-performance thermoelectric materials require the ability to exhibit high electrical transport properties and low thermal conductivity in large temperature range. Heat transport in materials can be characterized by phonon scattering. Typically, heat conduction in solid crystalline materials involves both transverse and longitudinal phonons, while liquid heat transport is achieved primarily by longitudinal phonons. Therefore, in general, solids exhibit stronger thermal conductivity than liquids.

Recently, researchers from Institute of High Energy Physics, Chinese Academy of Sciences/Spallation Neutron Source Science Center and collaborators investigated the phonon dynamics in a low-thermal-conductivity crystal, which is stable in wide temperature of 8-700 K, and observed liquid-like phonon transport behavior in this ordered crystal CsAg₅Te₃, through first-principles calculations and neutron scattering experiments. The study revealed that the ultra-low lattice thermal conductivity of this material can be mainly attributed to the weak chemical bonding and strong phonon anharmonicity, with the phonons exhibiting both wave-like and particle-like characteristics. The couplings between them result in weak temperature dependence and ultralow values of the lattice thermal conductivity. This research has been published in the National Science Review titled "Strong low-energy rattling modes enabled liquid-like ultralow thermal conductivity in a well-ordered solid", with associate professor Bao Tian Wang and professor Junrong Zhang from Institute of High Energy Physics, Chinese Academy of Sciences, professor Jiaqing He from Southern University of Science and Technology, and Professor Hua Lin from Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences as corresponding authors. Associate professor Pengfei Liu from Institute of High Energy Physics, Chinese Academy of Sciences and postdoctoral fellow Xiyang Li from Quantum Materials Research Institute at the University of British Columbia are the co-first authors of the paper.

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