Enhanced thermoelectric properties of (Pb1−xYbxTe)0.15(GeTe)0.85 composites due to phase separation and Yb doping

• The rhombohedral single phase of (Pb1−xYbxTe)0.15(GeTe)0.85 was first prepared.
• The SPS-treated sample separates into the PbTe-based and GeTe- based phases.
• The phase segregation reduces its lattice thermal conductivity.
• The thermoelectric properties can be enhanced by proper Yb doping.
• The maximum ZT of 1.38 at 723 K was found in (Pb0.9Yb0.1Te)0.15(GeTe)0.85.

The Yb doped Ge-rich (Pb1−xYbxTe)0.15(GeTe)0.85 composites with x = 0, 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20 were prepared by melting, solutioning and quenching, followed by a spark plasma sintering (SPS). The SPS-treated (Pb1−xYbxTe)0.15(GeTe)0.85 sample separates into a two-phase mixture with minor NaCl-type structure PbTe-based precipitates and the rhombohedral GeTe-based matrix based on the Spinodal decomposition in the PbTe–GeTe pseudo-binary system, leading to reduce its thermal conductivity. The Yb atoms prefer in PbTe-based phase. All samples show p-type conduction. The thermoelectric properties of the composites can be enhanced by proper Yb doping due to its further reducing the thermal conductivity and increasing the Seebeck coefficient although also increasing slightly the electrical resistivity of the composite. The (Pb1−xYbxTe)0.15(GeTe)0.85 composite with Yb content x = 0.1 show relative low resistivity of 7.36 × 10−6 Ω m, relative high Seebeck coefficient of 141 × 10−6 V K−1, lowest thermal conductivity of 1.4 W m−1 K−1 and the maximum ZT of 1.4 at 723 K, which is much higher than that of pure GeTe, PbTe or PbTe–GeTe alloys.