Thermoelectric Properties of Undoped High Purity Higher Manganese Silicides Grown by Chemical Vapor Transport
Thermoelectric Properties of Undoped High Purity Higher Manganese Silicides Grown by Chemical Vapor Transport
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DOI：
10.1021/cm5023823
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发表时间：
2014-09-09
影响因子：
8.6
通讯作者：
Jin, Song
中科院分区：
文献类型：
--
作者：
Girard, Steven N.;Chen, Xi;Jin, Song
标称成分为 MnSi1.73 的半导体高锰硅化物 (HMS) 因其元素丰度、无毒性而成为特别有前途的热电材料，据报道，未掺杂样品在 800 K 时的 ZT 约为 0.4。然而，HMS 材料的熔体生长过程中会自然形成嵌入的 MnSi 杂质。块状 HMS 中天然存在的 MnSi 杂质的影响尚未得到仔细研究。在此，我们报道了通过化学气相传输合成高纯度无MnSi的HMS单晶，以及通过放电等离子烧结（SPS）制备的固结HMS样品的热电性能。 HMS 晶体的高纯度通过扫描和透射电子显微镜、电子衍射和同步加速器高分辨率 X 射线衍射得到验证。尽管成功生长了高纯度 HMS 单晶，但我们发现在 SPS 处理后，MnSi 仍会从 HMS 中沉淀出来。原位同步加速器高分辨率X射线衍射实验表明HMS在高温下不稳定。尽管 HMS 材料中存在 MnSi 夹杂物的沉淀，但我们表明，由未掺杂的 HMS 单晶制备的样品由于其纯度较高而表现出较高的空穴迁移率，从而在 750 K 时将最大 ZT 提高到 0.52 +/- 0.08。
Semiconducting higher manganese silicides (HMS), with a nominal composition of MnSi1.73, are particularly promising thermoelectric materials because of their elemental abundance, nontoxicity, and reported ZT of around 0.4 at 800 K for undoped samples. However, embedded MnSi impurities naturally form during the melt growth of HMS materials. The influences of such naturally occurring MnSi impurities within bulk HMS have yet to be carefully studied. Herein, we report the synthesis of high-purity MnSi-free single crystals of HMS by chemical vapor transport and the thermoelectric properties of consolidated HMS samples prepared by spark plasma sintering (SPS). The high purity of the HMS crystals is verified by scanning and transmission electron microscopy, electron diffraction, and synchrotron high-resolution X-ray diffraction. Despite successfully growing high purity HMS single crystals, we find that MnSi will nevertheless precipitate from HMS after SPS processing. In-situ sychrotron high-resolution X-ray diffraction experiments show that HMS are unstable at high temperatures. Despite the precipitation of MnSi inclusions within the HMS materials, we show that samples prepared from undoped single crystals of HMS exhibit higher hole mobilities owing to their higher purity, resulting in an improved maximum ZT of 0.52 +/- 0.08 at 750 K.