High Thermoelectric Performance due to Nanoprecipitation, Band Convergence, and Interface Potential Barrier in PbTe-PbSe-PbS Quaternary Alloys and Composites

Abstract

Thermoelectric power generation is a direct heat to electric energy conversion technology and can be applied to waste heat power conversion as well. Among thermoelectric (TE) materials, PbTe−PbSe−PbS quaternary alloys and composites are promising candidates for thermoelectric power generation applications in mid-temperature operating range from 500 to ~850 K. On the other hand, the thermoelectric performance of quaternary alloys and composites is not fully optimized regarding composition and synthesis process. Here we present results of investigation of quaternary system PbTe−PbSe−PbS. We found that PbS will form nanoprecipitation in the matrix of quaternary alloy for small content of PbS (≤0.07) which induces the reduction of lattice thermal conductivity. The power factor of PbTe − PbSe − PbS quaternary alloys is significantly enhanced due to band convergence in PbTe1−xSex. As the result of simultaneous PbS nanoprecipitation with coherent interface with the matrix and band structure modification, we obtained extremely high ZT value of 2.3 at 800 K for (PbTe)0.95−x(PbSe)x(PbS)0.05. The chemical potential tuning by effective K doping (x = 0.02) and PbS substitution causes high power factor and low thermal conductivity, resulting in comparatively high ZT value of 1.72 at 800 K. The combination of high Seebeck coefficient and low thermal conductivity results in very high ZT value of 1.52 at 700 K for low Cl-doped (x = 0.0005) n-type (PbTe0.93−xSe0.07Clx)0.93(PbS)0.07 composites. Therefore, effective chemical potential tuning, band convergence, and nanoprecipitation give rise to significant enhancement of thermoelectric performance of both p- and n-type PbTe − PbSe − PbS quaternary alloy and composite TE materials.