High-performance n-type YbxCo4Sb12: from partially filled skutterudites towards composite thermoelectrics
High-performance n-type YbxCo4Sb12: from partially filled skutterudites towards composite thermoelectrics
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DOI：
10.1038/am.2016.77
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发表时间：
2016-07-01
影响因子：
9.7
通讯作者：
Yang, Jihui
中科院分区：
文献类型：
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作者：
Wang, Shanyu;Salvador, James R.;Yang, Jihui
方钴矿的填充分数极限（FFL），即不同物种之间形成平衡的复杂性，是实现高热电性能的一个复杂但关键的参数。在这项工作中，我们合成了一系列的YbxCo 4Sb 12样品（x = 0.2-0.6），并系统地研究了Yb的FFL，尽管这个系统已经被广泛研究了几十年，但仍然存在争议。我们的X射线衍射，显微结构和定量成分分析的综合实验工作清楚地揭示了Yb的FFL类似于0.29的CoSb 3，这与以前的理论计算是一致的。在x>0.35的样品中，过量的Yb主要形成金属YbSb 2沉淀，显著提高费米能级，从而增加电导率并降低塞贝克系数。基于Bergman复合材料理论的数值计算进一步证实了这一结果，该理论精确地再现了基于名义Yb0.35Co4Sb12和YbSb 2复合材料的x>0.35样品的输运性质。Yb0.3Co4Sb12在850 K时的最大ZT为1.5，这是单元素填充的CoSb 3的最高值。高ZT源于高功率因数（超过50 μ W cm-K-2）和低晶格热导率（远低于1.0 W m-K-1）。更重要的是，大的平均ZT，例如，对于300-850 K类似于1.05，对于500-850 K类似于1.27，与n型方钴矿的最佳值相当。Yb的高热电和热机械性能以及相对较低的空气和湿度敏感性使得Yb填充的CoSb 3成为大规模发电应用的有希望的候选者。
The filling fraction limit (FFL) of skutterudites, that is, the complex balance of formation enthalpies among different species, is an intricate but crucial parameter for achieving high thermoelectric performance. In this work, we synthesized a series of YbxCo4Sb12 samples with x = 0.2-0.6 and systemically studied the FFL of Yb, which is still debated even though this system has been extensively investigated for decades. Our combined experimental efforts of X-ray diffraction, microstructural and quantitative compositional analyses clearly reveal a Yb FFL of similar to 0.29 in CoSb3, which is consistent with previous theoretical calculations. The excess Yb in samples with x>0.35 mainly form metallic YbSb2 precipitates, significantly raising the Fermi level and thus increasing the electrical conductivity and decreasing the Seebeck coefficient. This result is further corroborated by the numerical calculations based on the Bergman's composite theory, which accurately reproduces the transport properties of the x>0.35 samples based on nominal Yb0.35Co4Sb12 and YbSb2 composites. A maximum ZT of 1.5 at 850 K is achieved for Yb0.3Co4Sb12, which is the highest value for a single-element-filled CoSb3. The high ZT originates from the high-power factor (in excess of 50 mu W cm-K-2) and low lattice thermal conductivity (well below 1.0 W m-K-1). More importantly, the large average ZTs, for example, similar to 1.05 for 300-850 K and similar to 1.27 for 500-850 K, are comparable to the best values for n-type skutterudites. The high thermoelectric and thermomechanical performances and the relatively low air and moisture sensitivities of Yb make Yb-filled CoSb3, a promising candidate for large-scale power generation applications.