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

Ge-rich Ge1-xPbxSe0.5Te0.5 (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 Ge1-xPbxSe0.5Te0.5; this value is higher than that of pure PbTe or GeTe compounds and any other reported PbTe GeTe composites. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.