arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2006.02013cond-mat.mtrl-sci
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Half-Heusler热电材料:NMR研究

Half-Heusler thermoelectric materials: NMR studies

Yefan Tian, Nader Ghassemi, Wuyang Ren, Zhu Hangtian, Shan Li, Qian Zhang, Zhiming Wang, Zhifeng Ren, Joseph H. Ross

摘要:

我们报告了对一系列半赫斯勒半导体(包括NbCoSn、ZrCoSb、TaFeSb和NbFeSb)的$^{59}$ Co、$^{93}$ Nb和$^{121}$ Sb的核磁共振(NMR)测量结合密度泛函理论(DFT)计算,以更好地了解它们的电子性质和一般组成依赖性趋势。这些材料作为潜在的高效率热电材料是令人感兴趣的。与其他材料相比,我们发现ZrCoSb往往有一个相对较大的量的局部无序,明显的反位缺陷。这有助于对应于带边缘附近的杂质带的小激发间隙。在NbCoSn和TaFeSb中,Curie-Weiss型行为被揭示,这表明相互作用的顺磁缺陷的小密度。观察到非常大的顺磁化学位移与Van Vleck机制,由于紧密间隔的$d$带之间的导带和价带分裂。与此同时,DFT方法通常成功地再现了这些半Heusler材料的化学位移趋势,并且我们确定了较大幅度的位移的增强,这与电子相互作用效应有关。总趋势与系列中$d$ -电子杂交的变化有关。

英文摘要:

We report $^{59}$Co, $^{93}$Nb, and $^{121}$Sb nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations on a series of half-Heusler semiconductors, including NbCoSn, ZrCoSb, TaFeSb and NbFeSb, to better understand their electronic properties and general composition-dependent trends. These materials are of interest as potentially high efficiency thermoelectric materials. Compared to the other materials, we find that ZrCoSb tends to have a relatively large amount of local disorder, apparently antisite defects. This contributes to a small excitation gap corresponding to an impurity band near the band edge. In NbCoSn and TaFeSb, Curie-Weiss-type behavior is revealed, which indicates a small density of interacting paramagnetic defects. Very large paramagnetic chemical shifts are observed associated with a Van Vleck mechanism due to closely spaced $d$ bands splitting between the conduction and valence bands. Meanwhile, DFT methods were generally successful in reproducing the chemical shift trend for these half-Heusler materials, and we identify an enhancement of the larger-magnitude shifts, which we connect to electron interaction effects. The general trend is connected to changes in $d$-electron hybridization across the series.

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