[Zurück]

N. Melnychenkc-Koblyuk, A. Grytsiv, S. Berger, H. Kaldarar, H. Michor, F. Röhrbacher, E. Royanian, E. Bauer, P. Rogl, H. Schmid, G. Giester:
"Ternary clathrates Ba-Cd-Ge: phase equilibria, crystal chemistry and physical properties";
Journal of Physics: Condensed Matter, 19 (2007), S. 1 - 23.

Ternary clathrates Ba-Cd-Ge: phase equilibria, crystal chemistry and physical properties

N Melnychenko-Koblyuk 1, A Grytsiv 1, St Berger 1, H Kaldarar 2, H Michor 2, F Röhrbacher 2, E Royanian 1,2, E Bauer 2, P Rogl 1,4, H Schmid 1 and G Giester 3
1 Institut für Physikalische Chemie, University of Vienna, A-1090 Vienna, Währingerstrasse 42, Austria
2 Institut für Festkörperphysik, TU Wien, A-1040 Wien, Wiedner Hauptstrasse 8-10, Austria
3 Institut für Mineralogie und Kristallographie, University of Vienna, A-1090 Vienna, Althanstrasse 14, Austria
4 Author to whom any correspondence should be addressed
E-mail: peter.franz.rogl@univie.ac.at

Abstract.
The present paper describes the formation, phase relations at subsolidus temperatures and at 800 °C, crystal chemistry and physical properties of a series of ternary clathrates as part of the solid solution Ba₈Cd_xGe_43-5x/8[]_3-3x/8, derived from binary Ba₈Ge₄₃[]₃ with a solubility limit of 8 Cd per formula unit at 800 °C. Structural investigations in all cases confirm cubic primitive symmetry with a lattice parameter a~ 1.1 nm, consistent with the space group type P m3n . Both the temperature dependent x-ray spectra and the heat capacity define a low-lying, almost localized, phonon branch.
Studies of transport properties show electrons to be the majority charge carriers in the systems. As the Cd content increases, the system is driven towards a metal-to-insulator transition, causing Ba₈Cd_4.7Ge_40.3[]_1.0 , for example, to show metallic behaviour at low temperatures while at high temperatures semiconducting features become obvious. A model based on a gap of the electronic density of states slightly above the Fermi energy perfectly explains such a scenario. Thermal conductivity exhibits a pronounced low temperature maximum, dominated by the lattice contribution, while at higher temperatures the electronic part becomes more important.

http://dx.doi.org/10.1088/0953-8984/19/4/046203