Thermoelectric Properties of the cubic AgPb 10 SbTe 12
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Thermoelectric Properties of the cubic AgPb10SbTe12 Kuei-Fang Hsua, Sim Loob, Wei Chenc, Ctirad Uherc, Tim Hoganb, Mercouri G Kanatzidisa a
Department of Chemistry and Center for Fundamental Materials Research, Michigan State University, East Lansing, MI 48824, USA b Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI 48824, USA c Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA.
ABSTRACT AgPb10SbTe12 is one member of the cubic family of materials AgPbmSbTem+2, which adopts NaCl structure where Ag, Pb and Sb atoms occupy the Na site and Te atoms occupy the Cl site. Ingots of this compound were prepared by a solid state reaction for thermoelectric measurements. AgPb10SbTe12 is a narrow band gap semiconductor with Eg~0.26 eV. In order to optimize the ZT of this member, compositions with deficiency of Ag and Bi-substitution were examined and found to exhibit enhanced power factor at 300 K. The Bi-substituted ingot had ZT~0.39 at 300 K and ZT~0.68 at 400 K. Carrier concentration and the mobility measurements are reported.
INTRODUCTION Recently, several new materials have been discovered to possess high ZT values at the medium high temperature. Rare earth-filled skutterudites RECo4Sb12 (RE = Yb, Eu) were reported to reach ZT >1 at 700 K due to the lower low lattice thermal conductivity caused by the ion rattling effect.1,2 ZrNiSn-based half-Heusler compounds were reported to have ZT = 0.7 at 800 K.3 The Sr8Ga16Ge30 clathrates4 and NaxCo2O4 oxides5 were also found to have potential thermoelectric applications at high temperature. Furthermore, low dimensional supperlattice materials were reported to enhance ZT values caused by the effects of increasing electronic density of states and lower lattice thermal conductivity within the supperlattice structures.6,7,8 Lead telluride is a well-known thermoelectric material used for power generation up to 900 K with a maximum ZT of ~0.89,while remarkably, PbTe-based QD superlattice materials were reported to reach ZT~2 around 500-700 K.10,11 We have focused on discovering high performance bulk thermoelectric materials suitable for different temperature ranges. One of the approaches is to search for new compounds with low dimensional structures based on the transport theory that ZT scales with a parameter B defined as: 3/ 2 2 1 2k BT kB Eq. (1) B=γ m m m µ x y z 3π 2 h 2 eκ l x where γ is the band degeneracy, mi is the effective mass of the carriers (electrons or holes) in the ith direction, µx is the carrier mobility along the transport direction, and κl is the lattice contribution to the thermal conductivity. Thus, for high ZT, large effective mass, high carrier mobility, and low lattice thermal conductivity are desirable.12 Along these lines we identified layered CsBi4Te613 a promising system showing a ZT of 0.8 at 225 K, which is 40% greater than that of the Bi2-xSbxTe3-
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alloys. These low dimensional systems are taking advantage of the large anisotropy in carrier effective mas
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