具有超低热导率的一维铋硒卤族化合物

Extremely low thermal conductivity from bismuth selenohalides with 1D soft crystal structure

本征低热导率材料的研究具有重要的科学意义,已引起广泛关注.本工作报道了一类具有简单一维晶体结构的超低热导率材料:铋硒卤族化合物(BiSeX,X=Br,I).研究发现,BiSeI的热导率在573K仅为~0.27Wm^-1K^-1,达到了最低本征热导率的理论极限值.本研究采用第一性原理计算结合粉末中子衍射和变温球差扫描透射电子显微镜表征,深入探究了其超低热导率的机制.研究表明,BiSeX的一维结构赋予了材料低热导特性:弱的成键特性、低的声子速度、声学支和光学支的强非简谐性以及Bi和卤族元素较大的偏移效应,从而有效阻碍了声子输运,使得BiSeX具有超低的热导率.本研究提出了在具有一维结构的材料中寻找低传导特性的新思路,该研究思路在热电材料和热障涂层材料等低热传导需求领域中具有广阔的应用前景.

Materials with intrinsically low thermal conductivity are of fundamental interests.Here we report a new sort of simple one-dimensional(1 D)crystal structured bismuth selenohalides(Bi Se X,X=Br,I)with extremely low thermal conductivity of^0.27 W m^-1K^-1 at 573 K.The mechanism of the extremely low thermal conductivity in 1 D Bi Se X 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 the1 D structure of Bi Se X 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.