Strong low-energy rattling modes enabled liquid-like ultralow thermal conductivity in a well-ordered solid

Peng-Fei Liu; Xiyang Li; Jingyu Li; Jianbo Zhu; Zhen Tong; Maiko Kofu; Masami Nirei; Juping Xu; Wen Yin; Fangwei Wang; Tianjiao Liang; Lin Xie; Yongsheng Zhang; David J Singh; Jie Ma; Hua Lin; Junrong Zhang; Jiaqing He; Bao-Tian Wang

doi:10.1093/nsr/nwae216

Strong low-energy rattling modes enabled liquid-like ultralow thermal conductivity in a well-ordered solid

Natl Sci Rev. 2024 Jun 22;11(12):nwae216. doi: 10.1093/nsr/nwae216. eCollection 2024 Dec.

Authors

Peng-Fei Liu^{1

2}, Xiyang Li^{3

4}, Jingyu Li^{1

2}, Jianbo Zhu⁵, Zhen Tong⁶, Maiko Kofu⁷, Masami Nirei⁷, Juping Xu^{1

2}, Wen Yin^{1

2}, Fangwei Wang^{2

3}, Tianjiao Liang^{1

2}, Lin Xie^{8

9}, Yongsheng Zhang¹⁰, David J Singh¹¹, Jie Ma¹², Hua Lin¹³, Junrong Zhang^{1

2}, Jiaqing He^{8

9}, Bao-Tian Wang^{1

2}

Affiliations

¹ Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
² Spallation Neutron Source Science Center, Dongguan 523803, China.
³ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China.
⁴ Department of Physics & Astronomy and Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver V6T 1Z4, Canada.
⁵ State Key Laboratory of Advanced Welding and Joining Harbin Institute of Technology, Harbin 150001, China.
⁶ School of Advanced Energy, Sun Yat-Sen University, Shenzhen 518107, China.
⁷ J-PARC Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan.
⁸ Shenzhen Key Laboratory of Thermoelectric Materials, Department of Physics, Southern University of Science and Technology, Shenzhen 518055, China.
⁹ Guangdong Provincial Key Laboratory of Advanced Thermoelectric Materials and Device Physics, Southern University of Science and Technology, Shenzhen 518055, China.
¹⁰ Advanced Research Institute of Multidisciplinary Sciences, Qufu Normal University, Qufu 273165, China.
¹¹ Department of Physics and Astronomy, University of Missouri, Columbia, 65211, USA.
¹² Key Laboratory of Artificial Structures and Quantum Control, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
¹³ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China.

Abstract

Crystalline solids exhibiting inherently low lattice thermal conductivity (κ _L) are of great importance in applications such as thermoelectrics and thermal barrier coatings. However, κ _L cannot be arbitrarily low and is limited by the minimum thermal conductivity related to phonon dispersions. In this work, we report the liquid-like thermal transport in a well-ordered crystalline CsAg₅Te₃, which exhibits an extremely low κ _L value of ∼0.18 Wm^-1K^-1. On the basis of first-principles calculations and inelastic neutron scattering measurements, we find that there are lots of low-lying optical phonon modes at ∼3.1 meV hosting the avoided-crossing behavior with acoustic phonons. These strongly localized modes are accompanied by weakly bound rattling Ag atoms with thermally induced large amplitudes of vibrations. Using the two-channel model, we demonstrate that coupling of the particle-like phonon modes and the heat-carrying wave-like phonons is essential for understanding the low κ _L, which is heavily deviated from the 1/T temperature dependence of the standard Peierls theory. In addition, our analysis indicates that the soft structural framework with liquid-like motions of the fluctuating Ag atoms is the underlying cause that leads to the suppression of the heat conduction in CsAg₅Te₃. These factors synergistically account for the ultralow κ _L value. Our results demonstrate that the liquid-like heat transfer could indeed exist in a well-ordered crystal.

Keywords: inelastic neutron scattering; phonon dynamic; thermal conductivity; thermoelectric.