[Zurück]

I. Bednar, E. Royanian, S. Paschen, E. Bauer, N. Nasir, A. Grytsiv, N. Melnychenko-Koblyuk, P. Rogl:
"Giant Thermopower at Low Temperatures in Novel Clathrates Ba-8{Cu,Zn} (x) Ge46-x";
Journal of Electronic Materials, 39 (2010), 9; S. 1687 - 1691.

In the present work we focus on cubic type I Ba-Ge-based clathrates, where Ge in $$\rm Ba_8Ge_{43} \square_3$$ (where □ is a vacancy) is substituted by Cu, Zn, Pd, and Si. Structural investigations in all cases confirm cubic primitive symmetry consistent with the space group type $$Pm\bar{3}n$$ of a typical type I clathrate structure with lattice parameter a ≈ 1.06 nm. Electronic transport has been studied in a broad temperature range from 4.2 K to about 800 K, demonstrating that substitution allows fine-tuning of the charge carrier density, shifting the materials into the proximity of a metal-to-insulator transition. This is evidenced from giant thermopower reaching values of 400 μV/K in the case of Ba8Cu5.2Zn0.8Ge40.0 at temperatures well below room temperature (T max S ≈ 150 K).

Keywords Type I clathrates - Ba8Ge46−x - transport properties - figure of merit - metal-to-insulator transition

http://dx.doi.org/10.1007/s11664-010-1231-3