Influence of shear strain on HPT-processed n-type skutterudites yielding ZT=2.1

Gerda Rogl, Sanyukta Ghosh, Oliver Renk, Kunio Yubuta, Andriy Grytsiv, Erhard Schafler, Michael Zehetbauer, Ramesh C. Mallik, Ernst Bauer, Peter Rogl

After our successful new and energy-saving production route to prepare bulk skutterudites with high ZTs from commercial powders via cold pressing (CP) and high-pressure torsion (HPT), we present in this paper a detailed study of the influence of shear strain and the preparation parameters, especially the temperature, on the micro-structural, thermoelectric and mechanical properties by analyzing specimens cut from various positions of the HPT disks of (Sm,Mm)0.15Co4Sb12. Across these large discs (30 mm in diameter and about 1 mm thickness) the shear strain γ rises linearly from the center of the sample to the rim reaching γ ∼ 450 (for 5 revolutions), a value first time realized for skutterudites. HPT-straining is essential for the introduction of high densities of crystal lattice defects, particularly dislocations, which result in a significant refining of the grains. Whereas the processing temperature mainly influences the density of the HPT consolidated samples and as a consequence, physical and mechanical properties, the applied shear strain rules the thermoelectric parameters. As an important feature, the Seebeck coefficient remained roughly unchanged under strain. Although the increasing shear strain caused the thermal conductivity to significantly decrease, this beneficial effect is accompanied by a concomitant significant increase of the electrical resistivity. Consequently, the interplay of the two controversial influences results in a maximum and record high thermoelectric figure of merit ZT ∼2.1.

Department of Materials Chemistry, Dynamics of Condensed Systems, Physics of Nanostructured Materials
External organisation(s)
Indian Institute of Science, Montanuniversität Leoben, Tohoku University, Technische Universität Wien
Journal of Alloys and Compounds
No. of pages
Publication date
Peer reviewed
Austrian Fields of Science 2012
104011 Materials chemistry, 103018 Materials physics
ASJC Scopus subject areas
Mechanics of Materials, Mechanical Engineering, Metals and Alloys, Materials Chemistry
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