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1267-DD06-05

Investigation of the thermoelectric properties of the PbTeSrTe system Kanishka Biswas1, Jiaqing He 1, 2, Qichun Zhang1, Guoyu Wang3, Ctirad Uher3, Vinayak P. Dravid2 and Mercouri G. Kanatzidis 1, 4 1

Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA 3 Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA 4 Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA 2

ABSTRACT PbTe-based materials are promising for efficient heat energy to electricity conversion. We present studies of the thermoelectric properties of the PbTe-SrTe system. X-ray diffraction patterns reveal that all the samples crystallize in the rock salt structure without noticeable secondary phase. Na2Te doping of the PbTe-SrTe materials resulting in a positive sign Hall coefficient indicating p-type conduction. Lattice thermal conductivity is significantly decreased with the insertion of SrTe in PbTe lattice. The ZT ~ 1.3 of these materials is derived from their very low thermal conductivities and reasonably high power factor at 800 K. INTRODUCTION Thermoelectric materials are able to directly convert and reversibly heat energy into electrical power and may have a significant impact on power generation and cooling. An efficient thermoelectric material must exhibit a high thermoelectric figure of merit, ZT, at the temperature of operation, T. The figure of merit is defined as: ZT = (S2σ/κ)T, where S is the Seebeck coefficient), σ is the electrical conductivity, and κ is the thermal conductivity [1, 2]. Typically, there are two ways to improve ZT of thermoelectric materials: one is to enhance the power factor (σS2) and the other is to lower the thermal conductivity [3, 4, 5]. Approaches to increase the power factor include introducing a resonance level in valence band, e.g., in Tl-PbTe [6, 7] or by synergistic nanostructuring [8]. Nanoscale inclusions in bulk materials can dramatically suppress the lattice thermal conductivity by scattering the longer wavelength heatcarrying phonons, as for example in AgPbmSbTem+2 [9], AgPbmSnnSbTe2+m+n [10], NaPbmSbTe2+m [11], KPbmSbTe2+m [12], PbTe-PbS [13] and BiSbTe [14]. In all these cases, however, the power factor is also reduced because the nanoinclusions increase carrier scattering which in turn adversely affects the carrier mobilities. To our knowledge, thermoelectric properties of PbTe-SrTe have not been investigated in the literature. Here we report that the PbTe-SrTe system doped with Na2Te, with a SrTe molar concentration of only 1% achieves high ZT values at high temperature for p-type bulk thermoelectric materials. We show that the high performance of these materials derives mainly from a low lattice thermal conductivity which can be tuned by changing the SrTe concentrations and reasonably high Seebeck coefficient at high temperatures. Hall coefficient measurements suggest that there is no significant hole scattering a