Search for Resonant-Like Impurity in Ag-Doped CoSb^sub 3^ Skutterudite: Theoretical and Experimental Study

• Published in: Journal of electronic materials 2014-06, Vol.43 (6), p.1681
• Main Authors: Nieroda, P, Kutorasinski, K, Tobola, J, Wojciechowski, K T
• Format: Article
• Language: English
• Subjects: Electric properties; Electrical engineering; Materials science; Semiconductors
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-013-2833-3

Issue Title: International Conference on Thermoelectrics 2013. Guest Editors: Jihui Yang, Hiroaki Anno, Matt Beekman, Ryoji Funahashi, Yuri Grin, Emmanuel Guilmeau, Jan Koenig, Bertrand Lenoir, Don Morelli, Lasse Rosendahl, James R. Salvador, Jeff Sharp, David Singh, Tsunehiro Takeuchi, Xiegeng Tang, Chunlei Wang, Hsin Wang, Wenqing Zhang, and Tie-Jun Zhu Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) calculations of Ag-doped CoSb^sub 3^ point to the presence of either an extra sharp peak of s-symmetry Ag density of states near the valence-band edge when filling the void (2a) or to conventional p-type doping when substituting Sb site (24g). These results suggest a resonant-like impurity level in the former or nearly rigid-band behavior in the latter. To confirm the theoretical predictions, a series of samples with nominal composition Co^sub 8^Sb^sub 24^:Ag^sub x^ (x = 0, 0.1, 0.3, 0.4, 0.5) were prepared. Structural and phase composition analyses were carried out by x-ray diffraction, scanning electron microscopy, and scanning thermoelectric microprobe. Investigations of the influence of Ag impurity on the electrical conductivity and Seebeck coefficient were performed over the temperature range from 300 K to 560 K. It was found that doping CoSb^sub 3^ with Ag leads to an increase of the thermoelectric power factor [alpha] ^sup 2^ σ in the temperature range from 300 K to 475 K of about an order of magnitude for all doped samples. However, electron probe microanalysis revealed accumulation of Ag mainly in grain boundaries while the presence of Ag in CoSb^sub 3^ crystallites was not confirmed. This observation corroborates the results of KKR-CPA calculations concerning the formation energy of the Ag^sub x^Co^sub 4^Sb^sub 12^ system, which is much lower than values calculated for A ^sub x^Co^sub 4^Sb^sub 12^ (A = Ca, Ba).[PUBLICATION ABSTRACT]