Nanostructuring and its Influence on the Thermoelectric Properties of the AgSbTe 2 -SnTe Quaternary System

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0886-F05-08.1

Nanostructuring and its Influence on the Thermoelectric Properties of the AgSbTe2-SnTe Quaternary System. J. Androulakis1, R. Pcionek1, E. Quarez1, O.Palchik2, H. Kong2, C. Uher2, J. J. Dangelo3, T. Hogan3, X. Tang4, T. Tritt4 and M. G. Kanatzidis1 1 Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA 2 Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA 3 Department of Electrical and Computer Engineering and Materials Science and Mechanics, Michigan State University, East Lansing, MI 48824, USA 4 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29643, USA ABSTRACT The structural and thermoelectric properties of the AgSbTe2-SnTe quaternary system were studied. Powder averaged x-ray diffraction of Ag0.85SnSb1.15Te3 indicates a cubic NaCltype structure in contrast with the single crystal refinements, which point towards tetragonal symmetry. Furthermore, high-resolution electron microscopy imaging revealed the system to be a nano-composite formed by thermodynamically driven compositional fluctuations rather than a solid solution as it was viewed in the past. The lattice thermal conductivity attains very low values, which is in accord with recent theories on thermal transport in heterogeneous systems. The charge transport properties of the system exhibit a rich physical behavior highlighted in the coexistence of an almost metallic carrier concentration (~5×1021 cm-3) with a large thermoelectric power response of ~160 μV/K at 650 K. This is attributed to a heavy hole effective mass that is almost six times that of the electron rest mass. INTRODUCTION Quaternary systems formed between binary narrow band gap, high mobility semiconductors (like PbTe, GeTe) and AgSbTe2 and have been widely considered for thermoelectric applications in the past [1]. A fruit of this research activity has been the (AgSbTe2)0.15(GeTe)0.85 compound, better known with the acronym TAGS, which is the state of the art p-type thermoelectric material for high temperature applications (ZTTAGS~1.2 at 720 K) [2]. Recently, interest in the transport properties of AgSbTe2 has been revived since introduction of AgSbTe2 phases in PbTe was shown to result in promising n-type thermoelectric materials (AgPbmSbTem+2, LAST) in bulk form (ZTLAST~1.7 at 700 K) [3]. This is most probably due to the formation of Ag-Sb rich nanostructures formed in the PbTe matrix which enhance the thermal resistivity [4]. Here we report on (Ag1-xSb1+x)mSnyTey+2m, an interesting material system with surprising charge transport properties. The compounds are off-stoichiometric derivatives of (AgSbTe2)(SnTe) formed from the combination of two isotypic narrow band-gap semiconductors, AgSbTe2 and SnTe which adopt the rock salt (NaCl) structure. We have identified compositions, which to the best of our knowledge exhibit the largest thermoelectric power response of ~160 μV K and heaviest carrier mass despite an enormous almost metallic carrier concentration (~5×1021 cm-3).

0886-F05-08.2

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