Thermoelectric Properties of the Nanostructured NaPb 18-x Sn x MTe 20 (M=Sb, Bi) Materials
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1044-U08-05
Thermoelectric Properties of the Nanostructured NaPb18-xSnxMTe20 (M=Sb, Bi) Materials Aurelie Gueguen1,2, Pierre Ferdinand Poudeu Poudeu1, Robert Pcionek2, Huijun Kong3, Ctirad Uher3, and Mercouri G. Kanatzidis1 1 Chemistry, Northwestern University, Evanston, IL, 60208 2 Chemistry, Michigan State University, East Lansing, MI, 48824 3 Physics, University of Michigan, Ann Arbor, MI, 48109 ABSTRACT The thermoelectric properties of materials with compositions NaPb18-xSnxMTe20 (M=Sb, Bi, x=0, 3, 5, 9, 13, 16 and 18) were investigated in the temperature range 300670K. All compositions exhibited p-type behavior over the measured temperature range. Electronic properties and transport were tuned through the manipulation of the Pb/Sn ratio. Increasing the Sn fraction results in an increase in electrical conductivity and a decrease in thermopower. The compositions NaPb13Sn5SbTe20 and NaPb9Sn9SbTe20 show a lattice thermal conductivity of ~1 W/m/K at room temperature.
INTRODUCTION The increasing need for energy conversion and conservation has renewed interest in the thermoelectric field. Efficient heat- to -electricity converters require materials with high figure of merit ZT. ZT is defined as (σS2T)/κ with σ, S and κ being respectively the electrical conductivity, the thermopower and the thermal conductivity of the compound. One method to obtain high ZT is to minimize the lattice contribution of the thermal conductivity while maintaining the power factor σS2, by using nanostructures. Over the last decade, significant improvements in ZT have been reported using reduced dimensionality at the nanoscale. Different ways of designing such systems have been reported: Bi2Te3/Sb2Te3 nanostructures superlattices [1] and PbSe0.98Te0.02/PbTe quantum dot superlattices [2] have claimed ZT values of ~2.4 at 300 K and 1.3 at room temperature. ZT values as high as 3 have been reported by Harman and coworkers for Bidoped n-type PbSe/PbTe quantum dot superlattice [3]. However, for industrial applications bulk analogs of these systems would be more suitable. Recently, our group reported on the n-type AgPbmSbTem+2 [4-5] and the p-type Na1-xPbmSbyTem+2 [6] systems that exhibit high thermoelectric figure of merit. The composition Na0.95Pb20SbTe22 reaches ZT of ~ 1.7 at 650 K. This outstanding value is due to its very low thermal conductivity (~ 1.8 W/m/K at room temperature and ~ 0.85 W/m/K at 675 K). High resolution transmission electron microscopy of these materials revealed the presence of coherently embedded nanostructures in what is essentially a PbTe matrix [6]. The substitution of Pb by Sn in AgPbmSbTem+2 deeply impacted the electronic properties by changing the behavior from n- to p-type [7]. In this paper, we described the effect of the
substitution of Pb by Sn on the electronic and thermal transport properties of NaPb18SbTe20. EXPERIMENTAL Samples were prepared by mixing stoichiometric high purity elemental sodium, lead, tin, antimony, and tellurium in carbon coated silica tubes. The tubes were then sealed under residual pre
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