Extraordinary thermoelectric performance in n-type manganese doped Mg3Sb2 Zintl: High band degeneracy, tuned carrier scattering mechanism and hierarchical microstructure
Extraordinary thermoelectric performance in n-type manganese doped Mg3Sb2 Zintl: High band degeneracy, tuned carrier scattering mechanism and hierarchical microstructure
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DOI：
10.1016/j.nanoen.2018.07.059
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发表时间：
2018-10-01
期刊：
影响因子：
17.6
通讯作者：
Sui, Jiehe
中科院分区：
文献类型：
--
作者：
Chen, Xiaoxi;Wu, Haijun;Sui, Jiehe
Zintl相由于其丰富的化学成分和复杂的结构，是热电应用的理想候选者。然而，由于本征缺陷导致的持久p型导电特性严重限制了其实际应用。目前已经设计了几种典型的n型Zintl材料，其中Te掺杂的Mg_3Sb_(1.5)Bi0.5是最有前途的。为了提高其整体热电性能，我们引入了锰来协同优化其电和热输运性质。实验和计算结果都表明，具有高能带简并度的多个导带是Seebeck系数增大的原因。在Mg位上掺入Mn改变了低温载流子散射机制，从电离杂质散射转变为与声学声子和电离杂质的混合散射，从而显著提高了载流子迁移率，从而提高了功率因数。同时，掺锰后薄膜的总导热系数显著降低。我们用像差校正的扫描电子显微镜(Cs校正的STEM)深入研究了它的分层结构，包括亚微米级的颗粒，在晶界偏析的纳米级的铋沉淀，纳米级的内生富铋沉淀，以及在这些缺陷周围产生的应变场。电和热输运的协同优化带来了非凡的性能，即在723K时的峰值ZT类似于1.85，平均ZT类似于1.25(从300K到723K)，这是迄今报道的任何n型热电材料中最高的。
Zintl phases are ideal candidates for thermoelectric applications due to their rich chemistry and structural complexity. However, the persistent p-type conduction due to intrinsic defects strongly restricts their practical applications. Recently, several typical n-type Zintl materials have been designed, where Te-doped Mg3Sb1.5Bi0.5 as the most promising. To enhance its overall thermoelectric performance, we introduce Mn to synergistically optimize the electrical and thermal transport properties. Both experimental and computational results demonstrate that multiple conduction bands with high band degeneracy are responsible for the enhanced Seebeck coefficient. Mn doping on Mg sites changes the low-temperature carrier scattering mechanism from ionized impurity scattering to mixed scattering with acoustic phonons and ionized impurities, resulting in a significant enhancement of carrier mobility and therefore power factor. Simultaneously, the total thermal conductivity is observably reduced after Mn doping. We employed aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) to thoroughly investigate its hierarchical microstructure, including sub-micron grains, nanoscale Bi precipitates segregated at grain boundaries, nanoscale endotaxial Bi-rich precipitates within the Mg3Sb2 based matrix, as well as the resulting strain fields around these defects. The synergistic optimization of electrical and thermal transport contributes to extraordinary performance, namely a peak ZT similar to 1.85 at 723 K and an average ZT similar to 1.25 (from 300 K to 723 K), which are the highest ever reported in any n-type thermoelectric material.