Origin of Ultralow Thermal Conductivity in n-Type Cubic Bulk AgBiS2: Soft Ag Vibrations and Local Structural Distortion Induced by the Bi 6s2 Lone Pair
Origin of Ultralow Thermal Conductivity in n-Type Cubic Bulk AgBiS2: Soft Ag Vibrations and Local Structural Distortion Induced by the Bi 6s2 Lone Pair
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DOI：
10.1021/acs.chemmater.9b00001
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发表时间：
2019-03
影响因子：
8.6
通讯作者：
Ekashmi Rathore;R. Juneja;Sean P. Culver;Nicoló Minafra;A. Singh;W. Zeier;K. Biswas
中科院分区：
文献类型：
--
作者：
Ekashmi Rathore;R. Juneja;Sean P. Culver;Nicoló Minafra;A. Singh;W. Zeier;K. Biswas
具有超低导热系数的晶体材料是热障涂层和热电转换的关键材料。无毒的n型块状立方体AgBiS_2在298-820K温度范围内表现出极低的晶格热导率(κ_(Lat))，为0.68-0.48W/mK，接近理论最低值(κ_(Min))。同步辐射X射线散射数据的对分布函数分析表明，κLat低的原因是以Ag为主的原子的软振动和明显的晶格非谐性，这是由于6s2孤对铋的立体化学活性引起的沿[011]方向的局部结构扭曲所致。由第一原理密度泛函理论计算的声子色散也表明，由于Ag诱导的低能爱因斯坦模的存在，AgBiS_2的低温热容有一个宽峰。由于银和铋贡献的低能光学声子对载热声子有很强的散射作用，从而降低了声学声子的能量密度.
Crystalline materials with ultralow thermal conductivity are essential for thermal barrier coating and thermoelectric energy conversion. Nontoxic n-type bulk cubic AgBiS2 exhibits exceptionally low lattice thermal conductivity (κlat) of 0.68–0.48 W/m K in the temperature range of 298–820 K, which is near the theoretical minimum (κmin). The low κlat is attributed to soft vibrations of predominantly Ag atoms and significant lattice anharmonicity because of local structural distortions along the [011] direction, arising because of the stereochemical activity of the 6s2 lone pair of Bi, as suggested by pair distribution function analysis of the synchrotron X-ray scattering data. The low-temperature heat capacity of AgBiS2 shows a broad hump because of the Ag-induced low-energy Einstein modes as also suggested from phonon dispersion calculated by first-principle density functional theory. Low-energy optical phonons contributed by Ag and Bi strongly scatter heat-carrying acoustic phonons, thereby decreasing the...