High thermoelectric performance of Ge1−xPbxSe0.5Te0.5 due to (Pb, Se) co-doping

Ge-rich Ge1−xPbxTe0.5Se0.5 (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4 and 0.5) alloys with high thermoelectric performance were prepared through a conventional melting, solutioning and quenching route, followed by a spark plasma sintering technique. Se doping extends the solid solubility of Pb in GeTe. The samples maintain the rhombohedral GeTe-based solid solution up to x = 0.3, while the samples with x = 0.4 and 0.5 are composites containing the major rhombohedral GeTe-based supersaturated solid solution and a mixture of the minor NaCl-type PbTe-based and rhombohedral GeTe-based phases separated from the supersaturated solid solution. All the samples show p-type conduction. The solute Pb and Se atoms in the GeTe lattice may modify the carrier concentration, leading to a significant increase in the Seebeck coefficient. The solute Pb and Se atoms, twinning microstructures and the grain boundaries or secondary phase may form broad-based phonon scattering centers, leading to alloys with extremely low thermal conductivity. In the results, the overall high thermoelectric properties were obtained in the alloys due to (Pb, Se) co-doping. A maximum ZT of 1.6 at 673 K was eventually achieved in Ge0.75Pb0.25Te0.5Se0.5; this value is higher than that of pure PbTe or GeTe compounds and any other reported PbTe–GeTe composites.