N Melnychenko-Koblyuk et al 2007 J. Phys.: Condens. Matter 19 216223 doi:10.1088/0953-8984/19/21/216223
Ternary clathrates Ba–Zn–Ge: phase equilibria, crystal chemistry and physical properties
N Melnychenko-Koblyuk1, A Grytsiv1, L Fornasari2,3, H Kaldarar2, H Michor2, F Röhrbacher2, M Koza4, E Royanian1,2, E Bauer2, P Rogl1,7, M Rotter1, H Schmid1, F Marabelli3, A Devishvili4, M Doerr5 and G Giester6
Show affiliationsThe formation, phase relations, crystal chemistry and physical properties were investigated for the solid solution 
deriving from binary clathrate 
with a solubility limit of 8 Zn atoms per formula unit at 800 °C (
is a vacancy). Single-crystal x-ray data throughout the homogeneity region confirm the clathrate type I structure with cubic primitive space group type 
.
Temperature-dependent x-ray spectra as well as heat capacity define a low-lying, almost localized, phonon branch, whereas neutron spectroscopy indicates a phonon mode with significant correlations. The transport properties are strongly determined by the Ge/Zn ratio in the framework of the structure. Increasing Zn content drives the system towards a metal-to-insulator transition; for example, 
shows metallic behaviour at low temperatures, whilst at high temperatures semiconducting features become obvious. A model based on a gap of the electronic density of states slightly above the Fermi energy was able to explain the temperature dependences of the transport properties. The thermal conductivity exhibits a pronounced low-temperature maximum, dominated by the lattice contribution, while at higher temperatures the electronic part gains weight. Zn-rich compositions reveal attractive Seebeck coefficients approaching −180 µV K−1 at 700 K.
- PACS
-
72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
63.20.-e Phonons in crystal lattices
71.30.+h Metal-insulator transitions and other electronic transitions
- Subjects
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Soft matter, liquids and polymers
- Dates
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Issue 21 (30 May 2007)
Received 27 November 2006, in final form 9 March 2007
Published 2 May 2007
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Ternary clathrates Ba–Zn–Ge: phase equilibria, crystal chemistry and physical properties
N Melnychenko-Koblyuk et al 2007 J. Phys.: Condens. Matter 19 216223
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