The CSNS data analysis group has successfully investigated the structure and phonon dynamics of the thermoelectric material CsAg5Te3, explaining the mechanism behind the anomalously low thermal conductivity of this well-ordered crystal. This researchwas published in National Science Review under the title "Strong low-energy rattling modes enabled liquid-like ultralow thermal conductivity in a well-ordered solid."

In solid materials, heat conduction involves both transverse and longitudinal phonons, whereas heat transport in liquids is primarily mediated by longitudinal phonons. As a result, solids typically exhibit stronger thermal conductivity than liquids. Through the Multi-Physics Instrument (MPI) at CSNS, the research team combined first-principles calculations, neutron diffraction experiments, inelastic neutron scattering experiments, and Boltzmann transport theory to conduct a detailed study of the structure and phonon dynamics of CsAg5Te3, a low thermal conductivity crystal material. They observed liquid-like phonon transport behavior in this well-ordered crystal. Neutron diffraction and pair distribution function (PDF) experiments conducted on the MPI revealed that the material maintains structural stability across a wide temperature range of 8–700 K, with no structural phase transitions or superionic transitions occurring. This work demonstrates that the intrinsic structural characteristics of well-ordered crystalline materials can lead to strong phonon scattering, enabling ultralow thermal conductivity in inorganic crystalline materials without the need for doping or other control methods. The findings provide important insights into understanding low lattice thermal conductivity and offer new ideas for designing thermoelectric materials, thermal management devices, thermal barrier coatings, and thermal insulators.

Prof. WANG Baotian from IHEP and Prof. HE Jiaqing from Southern University of Science and Technology served as co-corresponding authors of the paper. Prof. LIU Pengfei from the Institute of High Energy Physics and Dr. LI Xiyang from the Institute of Physics were co-first authors. The research received funding and support from the National Natural Science Foundation of China, Guangdong Province, and Shenzhen City.

Paper link: https://doi.org/10.1093/nsr/nwae216