The role of nanoscale defect features in enhancing the thermoelectric performance of p-type nanostructured SiGe alloys
The role of nanoscale defect features in enhancing the thermoelectric performance of p-type nanostructured SiGe alloys
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DOI：
10.1039/c5nr01786f
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发表时间：
2015-01-01
期刊：
影响因子：
6.7
通讯作者：
Dhar, Ajay
中科院分区：
文献类型：
--
作者：
Bathula, Sivaiah;Jayasimhadri, M.;Dhar, Ajay
尽管由于在放射性同位素温差发电器(RTG)中的应用，SiGe是研究最广泛的热电材料之一，但p型SiGe的热电优值系数(ZT)仍然很低，导致器件效率较低。在本研究中，我们报告了p型纳米结构Si80Ge20合金在900℃时类似于1.2的ZT的显著提高，方法是在Si80Ge20纳米结构基质中通过机械合金化和放电等离子烧结在纳米到介观尺度的光谱中产生几种类型的缺陷特征。ZT的这种提高，与p型纳米结构Si80Ge20合金的现有最先进值相似25%，主要是由于其在900℃时的超低导热系数类似于2.04Wm(-1)K-1，这是由于Si80Ge20纳米结构矩阵中不同类型的缺陷特征在纳米到介观尺度范围内对低到高波长载热声子的散射。这些缺陷包括点缺陷、位错、孤立的非晶区、纳米尺度的晶界，更重要的是，分布在整个Si80Ge20基质中的纳米到中尺度的残余孔隙率。这些纳米尺度的多维缺陷特征用扫描和透射电子显微镜进行了表征，并与电学和热输运性质相关联，在此基础上讨论了ZT的增强作用。
Despite SiGe being one of the most widely studied thermoelectric materials owing to its application in radioisotope thermoelectric generators (RTG), the thermoelectric figure-of merit (ZT) of p-type SiGe is still quite low, resulting in poor device efficiencies. In the present study, we report a substantial enhancement in ZT similar to 1.2 at 900 degrees C for p-type nanostructured Si80Ge20 alloys by creating several types of defect features within the Si80Ge20 nanostructured matrix in a spectrum of nano to meso-scale dimensions during its nanostructuring, by employing mechanical alloying followed by spark plasma sintering. This enhancement in ZT, which is similar to 25% over the existing state-of-the-art value for a p-type nanostructured Si80Ge20 alloy, is primarily due to its ultralow thermal conductivity of similar to 2.04 W m(-1) K-1 at 900 degrees C, resulting from the scattering of low-to-high wavelength heat-carrying phonons by different types of defect features in a range of nano to meso-scale dimensions in the Si80Ge20 nanostructured matrix. These include point defects, dislocations, isolated amorphous regions, nano-scale grain boundaries and more importantly, the nano to meso-scale residual porosity distributed throughout the Si80Ge20 matrix. These nanoscale multi-dimensional defect features have been characterized by employing scanning and transmission electron microscopy and correlated with the electrical and thermal transport properties, based on which the enhancement of ZT has been discussed.