Thermoelectric Performance of AgPb x SbTe20 (x = 17 to 23) Bulk Materials Derived from Large-Particle Raw Materials

AgPbxSbTe20 (x = 17 to 23) bulk materials with nanometer-sized grains were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) intentionally using large-sized lead and tellurium particles as raw materials to reduce oxygen impurity from surface oxides. It was found that the nominal Pb content in the starting powder mixture greatly affected the thermoelectric (TE) properties of the sintered bulk samples, with excess amount relative to the stoichiometric ratio of AgPbmSbTem+2 less than previously reported. x-Ray diffraction experiments revealed that the lattice parameter increases linearly with increasing Pb content until x = 20, which corresponds to the optimal nominal Pb content in the starting composition, showing the highest ZT value. A high ZT value of 1.2 at 675 K was achieved in the x = 20 sample due to its lowest electrical resistivity and reduced thermal conductivity. The present study shows that using large-sized Pb particles containing less oxygen is suitable for fabrication of AgPbmSbTem+2-system TE materials by MA and SPS processes.