title: Crystal structure and transport properties of Ba8Ge43square3.
abstract: The single phase clathrate-I Ba(8)Ge(43)square(3) (space group Ia3d (no. 230), a = 21.307(1) A) was synthesized by quenching the melt between cold steel plates. Specimens for physical property measurements were characterized by microstructure analysis and X-ray diffraction on polycrystalline samples as well as single crystals. Transport properties including thermopower, electrical resistivity, thermal conductivity and specific heat were investigated in a temperature range of 2-673 K. The electrical resistivity exhibits a metal-like temperature dependence below 300 K turning into a semiconductor-like behaviour above 300 K. The analysis of the specific heat at low temperature indicates a finite density of states at the Fermi level, thus corroborating the metallic character below 300 K. The temperature dependence of the specific heat was modelled assuming Einstein-like localized vibrations of Ba atoms inside the cages of the Ge framework. A conventional crystal-like behaviour of the thermal conductivity with a low lattice contribution (kappa(l)(300 K) = 2.7 W m(-1) K(-1)) has been evidenced.
authors.affiliation: Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187, Dresden, Germany.
authors.forename: U
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authors.lastname: Aydemir
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authors.lastname: Candolfi
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authors.lastname: Borrmann
authors.forename: M
authors.initials: M
authors.lastname: Baitinger
authors.forename: A
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authors.lastname: Ormeci
authors.forename: W
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authors.lastname: Carrillo-Cabrera
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authors.initials: C
authors.lastname: Chubilleau
authors.forename: B
authors.initials: B
authors.lastname: Lenoir
authors.forename: A
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authors.lastname: Dauscher
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authors.lastname: Oeschler
authors.forename: F
authors.initials: F
authors.lastname: Steglich
authors.forename: Yu
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authors.lastname: Grin