Thermoelectric properties of Zn-Sn-Sb based alloys
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Thermoelectric properties of Zn-Sn-Sb based alloys Motoki Ito1, Yuji Ohishi1, Hiroaki Muta1, Ken Kurosaki1, Shinsuke Yamanaka1,2 1 Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan 2 Research Institute of Nuclear Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 9108507, Japan. ABSTRACT In the Zn-Sn-Sb ternary system, Zn4Sb3, ZnSnSb2, and ZnSb have attracted attentions as advanced thermoelectric materials. Zn-Sn-Sb based alloys with various compositions were fabricated and the thermoelectric properties were investigated. That system is composed by orthorhombic ZnSb phase, tetragonal ZnSnSb2 phase with chalcopyrite structure, and rhombohedral SnSb phase. Large Sn content increases volume fraction of the metallic SnSb phase, which degenerate the powar factor. The ZnSb based alloy shows relatively large Seebeck coefficient. Sn substitution for ZnMxSb1-x significantly enhances the power factor, which indicates that Sn is effective dopant for ZnSb. INTRODUCTION A growth in the commercial applications of thermoelectric devices depends on increasing the dimensionless figure of merit ZT=S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is absolute temperature, respectively. This value needs to be significantly larger than 1.0 if thermoelectric conversions are to become a viable option for future energy generation. In the past, the degenerated semiconductor with narrow band gap, such as Bi2Te3 and LAST, has been seen as thermoelectric material, which has a complex structure1. However, those compounds include toxic Pb and Te, It is difficult to use them practically. Several Zn-(Sn)-Sb based alloys, such as Zn4Sb3, ZnSnSb2, and ZnSb were reported to have a narrow band gap and show high thermoelectric performance2-6. These compounds were promising as the low-toxic thermoelectric materials. However, the Zn-Sn-Sb ternary phase diagram was not investigated yet. In the present study, the phases and thermoelectric properties for Zn-Sn-Sb based alloys with various compositions were investigated. In addition, ZnSb is focused among Zn-(Sn)-Sb based alloys. ZnSb is p-type semiconductor and has an orthorhombic crystal structure with space group P/bca. The energy gap estimated from the intrinsic conduction temperature region is 0.2 eV. The narrow band gap and the high Seebeck coefficient (250 μV/K at room temperature6) indicate that this compound is promising for room-temperature applications. The thermoelectric performance, however, is hampered by its high thermal conductivity. To date, studies on physical properties7, microstructure effect8, and processing technique9 of ZnSb have been reported. However, the doping effect for ZnSb is rarely studied. We substituted Sn in Sb and investigated the effect on the thermoelectric properties. Zn1-xSnxSb(x=0.1~0.9) and ZnSnxSb1-x (x=0, 0.01, 0.02, 0.05) were prepared and the thermoelectric properties were investigated from room temperature to 723 K.
EXPERIMENT The samples were prepare
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