Effects of Antimony on the Thermoelectric Properties of the Cubic Pb 9.6 Sb y Te 10-x Se x Materials
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Effects of Antimony on the Thermoelectric Properties of the Cubic Pb9.6SbyTe10-xSex Materials Pierre F. P. Poudeua, Jonathan D’Angelob, Adam Downeyb, Robert Pcioneka, Joseph Sootsmana, Zhenhua Zhouc, Oleg Palchikc, Timothy P. Hoganb, Ctirad Uherc and 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 The thermoelectric properties of Pb9.6SbyTe10-xSex were investigated in the intermediate temperature range of 300 – 700 K. The effect of the variation of Sb content (y) on the electronic properties of the materials is remarkable. Samples with compositions Pb9.6Sb0.2Te10Sex (y = 0.2) show the best combination of low thermal conductivity with moderate electrical x conductivity and thermopower. For Pb9.6Sb0.2Te8Se2 (x = 2) a maximum figure of merit of ZT~ 1.1 was obtained around 700 K. This value is nearly 1.4 times higher than that of PbTe at 700 K. This enhancement of the figure of merit of Pb9.6Sb0.2Te8Se2 derives from its extremely low thermal conductivity (~0.7 at W/m.K at 700 K). High resolution transmission electron microscopy of Pb9.6Sb0.2Te10-xSex samples shows broadly distributed Sb-rich nanocrystals, which may be the key feature responsible for the suppression of the thermal conductivity. INTRODUCTION Interest in discovering new materials with enhanced thermoelectric figure of merit (ZT = (σ×T×S2)/κ, where S is the seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity and T is the absolute temperature) has been growing over the past two decades mainly due to the wide field of potential technological applications. Substantial efforts are currently focused on materials suitable for high temperature applications. Several techniques and materials systems are currently under investigation. These include synthesis of new bulk materials [1], construction of superlattice thin-films [2, 3, 4] and quantum dot superlattices [5, 6, 7], and doping of lead telluride and its solid solutions [8, 9]. Here we report on the thermoelectric properties of the n-type Pb9.6SbyTe10-xSex system. We show that with a proper choice of y and x, an excellent combination of high thermopower, high electrical conductivity and low thermal conductivity can be achieved. The effect of the variation of Sb content on the thermoelectric properties is remarkable. High resolution transmission electron microscopy (HRTEM) of selected samples shows Sb-rich nanodots distributed inside a PbTe-rich matrix. The Pb9.6SbyTe10-xSex system was inspired by the structure of Pb9.6Sb0.3Te10 (Pm-3m).This structure combines interesting features such as mixed occupancy, site vacancy and low symmetry (Pm-3m) providing additional flexibility to create compositional fluctuations (nanodots) inside the structure by operating selec
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