Se-Sm co-doping strategy for tuning the structural and thermoelectric properties of GeTe-PbTe based alloys

Abstract

Structural design shows great impact on enhancing the thermoelectric performance of the GeTe-PbTe based materials. The Sm and Se elements are introduced to co-dope the GeTe-PbTe based alloys using a conventional solid-solution method followed by spark plasma sintering technique and thermal annealing. The Se doping can increase the solubility of Pb in the GeTe-based matrix, leading to the suppression of the segregated PbTe-based phases. The Sm–Se co-doping introduced secondary phases and twinning microstructures along with the traditional atomic-scale point defects and grain boundaries contribute to the wide-wavelength phonon scattering, leading to the reduction of lattice thermal conductivity. The co-doping strategy also shows impact on the tuning of carrier concentration and band structures for the optimization of power factor. The minimum lattice thermal conductivity reach to 0.41 Wm−1 K−1 for the sample Ge0.75Pb0.2Sm0.03Te0.7Se0.3 at 573 K, which approaches to the amorphous limit of GeTe. The maximum figure of merit ZT value can be increased to 1.03 for the sample Ge0.75Pb0.2Sm0.03Te0.5Se0.5 at 673 K, making the co-doping strategy quite attractive for further enhancing the thermoelectric performance of GeTe-PbTe based materials.