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Structure and stability of Ba-Cu-Ge type-I clathrates

Yang Li·Ji Chi·Weiping Gou·Sameer Khandekar·Joseph H. Ross Jr
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Abstract

We have prepared samples of nominal type Ba(8)Cu(x)Ge(46-x) by induction melting and solid state reaction. Analysis shows that these materials form type-I clathrates, with copper content between x = 4.9 and 5.3, nearly independent of the starting composition. We used x-ray powder diffraction and single-crystal electron diffraction to confirm the cubic type-I clathrate structure, while electron microprobe measurements confirmed the stability of the x = 5 composition. This result differs from the corresponding Ag and Au clathrates, and was not known previously due perhaps to the similar Cu and Ge form factors in x-ray diffraction. The observed composition adheres very tightly to a valence-counting scheme, in agreement with a Zintl-type stability mechanism. This implies a gap in the electronic density of states, also in contrast to the metallic behavior of the Au and Ag analogs. Magnetization measurements showed a large diamagnetic response in the Ba-Cu-Ge clathrate. This behavior is consistent with semiconducting or semimetallic behavior, and is similar to that of a number of intermetallic semiconductors.

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Yang Li, Ji Chi, Weiping Gou, Sameer Khandekar, Joseph H. Ross Jr. 2003-03-31. Structure and stability of Ba-Cu-Ge type-I clathrates. https://doi.org/10.1088/0953-8984%2F15%2F32%2F313

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