Comparison of local distortions in Ba8Ga16X30 (X = Si, Ge, Sn): An EXAFS study
Comparison of local distortions in Ba8Ga16X30 (X = Si, Ge, Sn): An EXAFS study
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DOI：
10.1039/c5tc01641j
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发表时间：
2015-10
影响因子：
6.4
通讯作者：
T. Keiber;P. Nast;S. Medling;F. Bridges;K. Suekuni;M. Avila;T. Takabatake
中科院分区：
文献类型：
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作者：
T. Keiber;P. Nast;S. Medling;F. Bridges;K. Suekuni;M. Avila;T. Takabatake
我们报告了扩展X射线精细结构（EXAFS）分析的第一型笼形化合物Ba_8Ga_（16）X_（30）（X = Si，Sn）和比较的结果与以前的研究结果X = Ge。Ga在三个晶体学笼位上的分布不是随机的，Ga优先具有X作为最近邻。我们的结果表明，对于X = Si，Sn，笼内的平均对距离（Ga-Sn，Ga-Ga，Ga-Si，Sn-Sn）与X射线衍射中发现的距离有很大不同，有些键短得多，有些键长得多。这些结果表明笼的显著屈曲，特别是对于Ba8Ga16Sn30。从Ba K边EXAFS中提取的Ba的环境从Ge到Si再到Sn变得越来越无序，并且对于Ba_8Ga_（16）Sn_（30），Ba的最近邻距离非常短，与严重的屈曲相一致。这种弯曲有助于增加Ba8Ga16Si30和Ba8Ga16Sn30的局部无序，并提供了比Ba8Ga16Ge30更高的电阻率和更低的ZT的解释。
We report an extended X-ray fine structure (EXAFS) analysis of the type-I clathrates Ba8Ga16X30 (X = Si, Sn) and compare the results with the results of previous studies on X = Ge. The distribution of Ga on the three crystallographic cage sites is not random, with the Ga preferentially having X as the nearest neighbor. Our results show that for X = Si, Sn the average pair distances within the cages (Ga–Sn, Ga–Ga, Ga–Si, Sn–Sn) are significantly different from the distances found in X-ray diffraction, with some much shorter bonds and some much longer bonds. These results suggest a substantial buckling of the cages, particularly for Ba8Ga16Sn30. The environment about Ba, extracted from Ba K edge EXAFS, becomes increasingly disordered from Ge to Si to Sn, and for Ba8Ga16Sn30 the nearest Ba neighbor distance is very short, consistent with severe buckling. This buckling contributes to the increased local disorder for Ba8Ga16Si30 and Ba8Ga16Sn30, and provides an explanation for a higher resistivity and a lower ZT than for Ba8Ga16Ge30.