Imasato Kazuki, Fu Chenguang, Pan Yu, Wood Max, Kuo Jimmy Jiahong, Felser Claudia, Snyder G Jeffrey
Materials Science & Engineering (MSE), Northwestern University, Evanston, IL, 60208, USA.
Department of Solid State Chemistry, Max Planck Institute for Chemical Physics of Solids, 01187, Dresden, Germany.
Adv Mater. 2020 Apr;32(16):e1908218. doi: 10.1002/adma.201908218. Epub 2020 Mar 1.
Mg (Sb,Bi) alloys have recently been discovered as a competitive alternative to the state-of-the-art n-type Bi (Te,Se) thermoelectric alloys. Previous theoretical studies predict that single crystals Mg (Sb,Bi) can exhibit higher thermoelectric performance near room temperature by eliminating grain boundary resistance. However, the intrinsic Mg defect chemistry makes it challenging to grow n-type Mg (Sb,Bi) single crystals. Here, the first thermoelectric properties of n-type Te-doped Mg Sb single crystals, synthesized by a combination of Sb-flux method and Mg-vapor annealing, is reported. The electrical conductivity and carrier mobility of single crystals exhibit a metallic behavior with a typical T dependence, indicating that phonon scattering dominates the charge carrier transport. The absence of any evidence of ionized impurity scattering in Te-doped Mg Sb single crystals proves that the thermally activated mobility previously observed in polycrystalline materials is caused by grain boundary resistance. Eliminating this grain boundary resistance in the single crystals results in a large enhancement of the weighted mobility and figure of merit zT by more than 100% near room temperature. This work experimentally demonstrates the accurate understanding of charge-carrier scattering is crucial for developing high-performance thermoelectric materials and indicates that single-crystalline Mg (Sb,Bi) solid solutions can exhibit higher zT compared to polycrystalline samples.
镁（锑，铋）合金最近被发现是一种可替代最先进的n型铋（碲，硒）热电合金的有竞争力的材料。先前的理论研究预测，通过消除晶界电阻，单晶镁（锑，铋）在室温附近可展现出更高的热电性能。然而，镁的固有缺陷化学性质使得生长n型镁（锑，铋）单晶具有挑战性。在此，报道了通过锑助熔剂法和镁蒸汽退火相结合合成的n型碲掺杂镁锑单晶的首次热电性能。单晶的电导率和载流子迁移率呈现出典型的与温度相关的金属行为，表明声子散射主导了电荷载流子的传输。在碲掺杂镁锑单晶中没有任何电离杂质散射的证据，这证明了先前在多晶材料中观察到的热激活迁移率是由晶界电阻引起的。消除单晶中的这种晶界电阻会导致加权迁移率和优值zT在室温附近大幅提高超过100%。这项工作通过实验证明了准确理解电荷载流子散射对于开发高性能热电材料至关重要，并表明与多晶样品相比，单晶镁（锑，铋）固溶体可展现出更高的zT。
