Materials with intrinsically low thermal conductivity are of fundamental interests. Here we report a new sort of simple one-dimensional (1D) crystal structured bismuth selenohalides (BiSeX, X = Br, I) with extremely low thermal conductivity of ∼0.27 W m⁻¹ K⁻¹ at 573 K. The mechanism of the extremely low thermal conductivity in 1D BiSeX is elucidated systematically using the first-principles calculations, neutron powder-diffraction measurements and temperature tunable aberration-corrected scanning transmission electron microscopy (STEM). Results reveal that the 1D structure of BiSeX possesses unique soft bonding character, low phonon velocity, strong anharmonicity of both acoustic and optical phonon modes, and large off-center displacement of Bi and halogen atoms. Cooperatively, all these features contribute to the minimal phonon transport. These findings provide a novel selection rule to search low thermal conductivity materials with potential applications in thermoelectrics and thermal barrier coatings.

本质上具有低导热率的材料是最重要的。在这里，我们报告了一种新型的简单一维（1D）晶体结构的硒化铋铋（BiSeX，X = Br，I），其导热系数极低，仅为〜0.27 W m ^-1 K ^-1使用第一性原理计算，中子粉末衍射测量和温度可调像差校正扫描透射电子显微镜（STEM）系统地阐明了一维BiSeX中极低导热率的机理。结果表明，BiSeX的一维结构具有独特的软键合特性，低声子速度，声和光声子模态的强非谐性以及Bi和卤素原子的大偏心位移。通过协作，所有这些功能都有助于最小化声子传输。这些发现为寻找在热电和热障涂层中具有潜在应用的低导热率材料提供了一种新颖的选择规则。