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

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

2002-10-10

arxiv.org/abs/cond-mat/0210244v3

J. Phys.: Condens. Matter v. 15, p. 5535 (2003)

Physics

Condensed Matter

Materials Science

5 pages, 3 figures. REVTeX 4.0

Scientific paper

10.1088/0953-8984/15/32/313

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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