近日，中国科学院高能物理研究所的王保田及其研究小组与南方科技大学的何佳清以及中国科学院福建物质结构研究所的林华等人合作并取得一项新进展。经过不懈努力，他们发现良序固体中强低能rattling模式能够实现类液体的超低热导率。相关研究成果已于2024年6月22日在国际知名学术期刊《国家科学评论》上发表。

在这项研究中，研究人员报道了良序晶体CsAg₅Te₃的液态热输运特性，其液态热导率（κ_L）极低，约为0.18 Wm^-1K^-1。基于第一性原理计算和非弹性中子散射测量的结果，他们发现存在多个位于约3.1 meV的低洼光学声子模式，这些模式与声子之间存在回避交叉的行为。这些强烈的局域模式伴随着热诱导下的大振幅振动，其特征是弱束缚的“rattling”银原子。

通过使用双通道模型，研究人员证明了类粒子声子模式和携带热量的类波声子之间的耦合对于理解低κL值是至关重要的，这与标准Peierls理论的1/T温度依赖性存在显著偏离。此外，这项分析还揭示了由波动Ag原子构成的液体运动软结构框架是CsAg₅Te₃中热传导受到抑制的根本原因。这些因素的协同作用导致了极低的κ_L值。这项研究结果表明，在有序晶体中确实可以存在类似于液体的热传递特性。

据悉，具有固有低晶格导热系数(κ_L)的结晶固体在热电和热障涂层等应用中具有重要意义。然而，κ_L不能任意低，并且受到与声子色散相关的最小热导率的限制。

附：英文原文

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

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

Issue&Volume: 2024-06-22

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 about 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.

DOI: 10.1093/nsr/nwae216

Source: https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwae216/7697558?searchresult=1