The efficiency of thermoelectric generators is defined by the thermoelectric performance of materials, as expressed by the thermoelectric figure-of-merit, and their contacts with electrodes. Lead chalcogenide thermoelectric materials, and in particular PbTe, perform well in the 500-900 K temperature range. Here, we have successfully bonded bulk PbTe to Ni electrode to generate a diffusion barrier, avoiding continuous reaction of the thermoelectric legs and conducting electrodes at the operating temperature. We have modified the commonly used spark plasma sintering assembly method to join Ni electrode to bulk PbTe by driving the total supplied electrical current through the Ni and PbTe solid interfaces. This permits the formation of a thin diffusion layer, roughly 4.5 µm in thickness, which is solely 2 comprised of nickel telluride. This new technique towards the bonding of PbTe with the electrode is beneficial for thermoelectric materials, since high temperatures have proven to be damaging to the quality of bulk material. The interphase microstructure, chemical composition, and crystallographic information were evaluated by a scanning electron microscope equipped with electron back-scattered diffraction analysis. The obtained phase at the Ni/PbTe contact is found to be β 2 Ni 3±x Te 2 with a basic tetragonal crystallographic structure of the defective Cu 2 Sb type.

Recently, the quaternary system PbTe-PbSe-PbS has been shown to provide high thermoelectric efficiency, zT. The intent of this research is to investigate the thermoelectric properties of Na-doped pseudoternary (PbTe) 0.65-x (PbSe) 0.35 (PbS) x with a high ratio of PbS toPbTe. The addition of a large concentration of PbSe increases the solubility limit of PbS in PbTe, allowing all samples to behave as solid solutions with a high concentration of PbS. This is proved to decrease lattice thermal conductivity due to the larger atomic mass contrast between Sulphur and Tellurium, however, simultaneously causes a decrease in the Seebeck coefficient due to a larger band offset, so a high concentration of PbS shows no improvement in zT, with a maximum of ~1.4 in the x = 0, 0.05 and 0.10 samples.

Metal chalcogenides have delivered the highest efficiencies among thermoelectric materials. Although the thermal stability of thermoelectric materials at device operating temperatures has been of concern, recent studies have reported the efficiencies of materials prepared with different fabrication techniques. Here, we have fabricated a p-type, multiphase lead chalcogenide compound of (PbTe)0.55(PbS)0.35(PbSe)0.1, with three common fabrication techniques of quenched, quenched-annealed and furnace cooled followed by spark plasma sintering. The compound contains PbS-rich precipitates within a PbTe-rich matrix. The achieved samples from various fabrication procedures demonstrate distinct microstructures that evolve with thermal cycling. We have shown that the thermoelectric efficiency of metastable compound is irreversible during thermal cycling, and changes by only three thermal cycles during measurements. Our findings highlight the importance of the choice of fabrication and post-processing techniques for thermoelectric materials.

Lead chalcogenide quaternary systems have been shown to provide high thermoelectric (TE) efficiency superior to those of binary and ternary lead chalcogenides, arising from both altered electronic band structures and a reduction in lattice thermal conductivity. Here, we have synthesized single-phase samples of the quaternary compound (PbTe) 0.55 (PbS) 0.1 (PbSe) 0.35 doped with Na and characterized their TE properties. We show that the dopant solubility is limited to 1 at. %. A very low lattice thermal conductivity of ∼0.6 W m –1 K –1 at 850 K is achieved at all dopant concentrations because of phonon scattering from point defects associated with solute atoms with high contrast atomic mass. As a result, a high TE figure of merit of approximately 1.5 is achieved at 823 K in heavily doped samples. Moreover, the figure of merit is greater than 1 over a wide temperature range above 675 K.