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N. Melnychenkc-Koblyuk, A. Grytsiv, P. Rogl, M. Rotter, R. Lackner, E. Bauer, L. Fornasari, F. Marabelli, G. Giester:
"Structure and physical properties of type-I clathrate solid-solution Ba₈Pt_xGe_{46−x−y y} ( =vacancy)";
Physical Review B, 76 (2007), 195124-1 - 195124-7.

Structure and physical properties of type-I clathrate solid-solution Ba₈Pt_xGe_{46−x−y y} ( =vacancy)

N. Melnychenko-Koblyuk, A. Grytsiv, P. Rogl, and M. Rotter
Institute of Physical Chemistry, University of Vienna, A-1090 Wien, Austria

R. Lackner and E. Bauer
Institute of Solid State Physics, Vienna University of Technology, A-1040 Wien, Austria

L. Fornasari and F. Marabelli
Physics Department "Alessandro Volta," University of Pavia, I-27100 Pavia, Italy

G. Giester
Institute of Mineralogy and Crystallography, University of Vienna, Althanstrasse 14, A-1090 Wien, Austria

(Received 18 July 2007; revised 19 September 2007; published 28 November 2007)

Formation, crystal chemistry, and physical properties were investigated for the solid-solution Ba₈Pt_xGe_{46−x−y y} is a vacancy) deriving from binary clathrate Ba₈Ge_{43[square, open]3} with a solubility limit of ~3.5 Pt atoms/f.u. at T=800 °C. Structural investigations throughout the homogeneity region confirm isotypism with the cubic primitive clathrate type-I structure (space group type Pm3n) and lattice parameters ranging from a=1.0657(2) nm for Ba₈Ge_{43 3} to a=1.0752(2) nm for Ba₈Pt_3.5Ge_{41.5 1.0}. Phase relations for the region concerning the clathrate solution were derived at subsolidus temperatures as well as at 800 °C. Transport properties evidence electrons as the majority charge carriers in the system with a slight dependency on the Pt content. The system is located close to a semiconducting regime with a gap in the electronic density of states of a few thousand K. No low temperature maximum is obvious from thermal conductivity which is dominated by the lattice contribution. Thermal conductivity furthermore documents a high efficiency of phonon scattering on vacancies.

http://dx.doi.org/10.1103/PhysRevB.76.195124

http://link.aps.org/abstract/PRB/v76/e195124