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Published January 31, 2014 | Published
Journal Article Open

Transport properties and valence band feature of high-performance (GeTe)_(85)(AgSbTe_2)_(15) thermoelectric materials


This paper aims at elucidating the origin of the high thermoelectric power factor of p-type (AgxSbTe_(x/2+1.5)15)(GeTe)_(85) (TAGS) thermoelectric materials with 0.4 ≤ x ≤ 1.2. All samples exhibit good thermoelectric figures of merit (zT) which reach 1.5 at 700 K for x = 0.6. Thermoelectric and thermomagnetic transport properties (electrical resistivity, Seebeck, Hall and transverse Nernst–Ettinghausen coefficients) are measured and used to calculate the scattering factor, the Fermi energy, the density-of-states (DOS) effective mass and hole mean free path (mfp). The DOS effective mass is very high due to the large band mass of the primary valence band and the high degeneracy of pockets in the Fermi surface from the second valence band. The highly degenerate Fermi surface increased the total DOS without decreasing mobility, which is more desirable than the high DOS that comes from a single carrier pocket. The high-temperature hole mfp approaches the Ioffe–Regel limit for band-type conduction, which validates our discussion based on band transport and is also important for TAGS alloys having high zT with heavy bands. The present results show that multiple degenerate Fermi surface pockets provide an effective way of substantially increasing the power factor of thermoelectric materials with low thermal conductivity.

Additional Information

© 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Authors, their institutions and third parties all have the same rights to reuse articles published in New Journal of Physics in accordance with the Creative Commons Attribution 3.0 Unported (CC-BY) license. Received 17 September 2013, revised 27 December 2013. Accepted for publication 7 January 2014. Published 31 January 2014. The work at Zhejiang University is supported by the National Basic Research Program of China (2013CB632503), the Natural Science Foundation of China (51171171 and 51271165), the Program for Innovative Research Team in University of the Ministry of Education of China (IRT13037), the Program for New Century Excellent Talents in University (NCET-12-0495) and the PhD program Foundation of the Ministry of Education of China (numbers 20120101110082 and 20110101110024). The work at Ohio State University is supported as part of the Revolutionary Materials for Solid State Energy Conversion Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award number DE-SC0001054.

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