Large enhancement in the thermoelectric properties of Pb0.98Na0.02Te by optimizing the synthesis conditions

Abstract

PbTe is known as a good thermoelectric material for waste heat recovery in the temperature range of 500 to 900 K. While various approaches such as nanostructuring for thermal conductivity reduction, resonant impurities, and band convergence by alloying for power factor enhancement have been proposed recently for enhancing the thermoelectric properties of PbTe, a systematic study on optimizing the synthesis conditions is also crucial to find a better base material, upon which those new approaches can be applied to further improve the material. In this paper, we systematically investigate the effect of various hot-press conditions on the thermoelectric properties of p-type 2% Na-doped PbTe, by varying the hot-press pressure from 70 to 130 MPa and the sintering time from 0.5 to 2 h. It is shown that the micro- and nano-scale structures in the hot-pressed material can be controlled by changing the sintering time and pressure. We demonstrate that by optimizing the hot-press conditions, the thermoelectric figure of merit of p-type 2% Na-doped PbTe can be enhanced up to zT = 1.74 at 774 K, which is about a 24% enhancement compared to the value of 1.4 presented by Pei et al. for the same material composition. Our electron transport modeling on bulk PbTe shows that this enhancement is due to the thermal conductivity reduction in both the electronic and lattice contributions. We believe that our findings can be accompanied with other recently-proposed techniques to further enhance the zT of this important thermoelectric material.