Enhancement of thermoelectric performance of PbTe by embedding NaCl

Abstract

Different contents of NaCl (2%, 4%, 6%, and 8 wt%) was incorporated in polycrystalline PbTe samples and consolidated via spark-plasma-sintering (SPS). NaCl acted as a dopant material during SPS. The effect of doping through NaCl increased the carrier concentration without deteriorating mobility. The incorporation of NaCl helped the formation of a porous structure which facilitated high rate of phonon scattering and decreased the thermal conductivity. Experimental observation suggests that the origin of electrical property is due to the extra carriers given by Na, and that Fermi level is well optimized by the compensation effect acquired by Cl doping. The energy barrier heights (EB) for charge carriers in PbTe/NaCl samples is lower than the EB of reference PbTe. High Seebeck coefficient of 300 µV/K at 773 K combined with the lower thermal conductivity of 0.55 W/m-K, yielded an improved figure-of-merit (zT) value as high as 1.2 at 773 K in a 6wt%NaCl:PbTe. In the PbTe/NaCl series, PbTe exhibited the reduced lattice thermal conductivity, enhanced charge carrier concentration as well as mobility, and high zT values. As a result, the incorporation of NaCl acted as a dopant well as aided in pore formation, which can be a potential pathway to optimize thermoelectric performances.