Effect of Bi doping on thermoelectric properties of Ge0.90−xPb0.10BixTe compounds

Doping is an effective way to optimize the performance of thermoelectric materials. In order to investigate the effect of Bi doping on microstructures and thermoelectric properties of Ge0.90Pb0.10Te, a series of Ge0.90−xPb0.10BixTe compounds were prepared by a melting-quenching-annealing process followed by spark plasma sintering. The Bi doping on Ge site acts as an electron donor, which effectively optimized the carrier concentration from 1.1 × 1021 cm−3 to 3.5 × 1020 cm−3. Besides, the lattice distortions originated from Bi doping further promoted the solubility of Pb in the GeTe matrix, which have great advantage for obtaining lower thermal conductivity compared with pristine Ge0.90Pb0.10Te sample. Low lattice thermal conductivity of about 0.77 W/mK was obtained in Ge0.86Pb0.10Bi0.04Te owing to the additional lattice defects introduced by Bi doping. Consequently, the highest ZT of 1.1 was obtained in Ge0.86Pb0.10Bi0.04Te at 600 K with an average ZT of 0.6. These results have confirmed that Bi doing is an efficient way to boost the thermoelectric performance of GeTe-based alloys.