Realization of non-equilibrium process for high thermoelectric performance Sb-doped GeTe

Pristine GeTe shows inferior thermoelectric performance around unit due to the large carrier concentration induced by the presence of intrinsic high concentration of Ge vacancy. In this study, we report a thermoelectric figure of merit ZT of 1.56 at 700 K, realized in Sb-doped GeTe based thermoelectric (TE) materials via combined effect of suppression of intrinsic Ge vacancy and Sb doping. The non-equilibrium nature during melt spinning process plays very important role. For one thing, it promotes the homogeneity in Ge_1-xSb_xTe samples and refines the grain size of the product. Moreover the persistent Ge precipitated as impurity phase in the traditional synthesis process is found to be dissolved back into the GeTe sublattice, accompanying with a drastic suppression of Ge vacancies concentration which in combination with Sb electron doping significantly reduced the inherent carrier concentration in GeTe. Low carrier concentration, approaching the optimum carrier concentration ∼3.74 × 10^-20 cm^-3 and a high power factor of 4.01 × 10^-3 W m^-1 K^-2 at 750 K are achieved for Ge_0.98Sb_0.02Te sample. In addition, the enhanced grain boundary phonon scattering by refining the grain size through melt spinning (MS) process, coupled with the intensified alloying phonon scattering via Sb doping leads to low thermal conductivity of 1.53 W m^-1 K^-1 at 700 K for Ge_0.94Sb_0.06Te sample. All those contribute to a high ZT value, representing over 50% improvement in the ZT value compared to the Sb free samples, which provides an alternative way for ultrafast synthesis of high performance GeTe based thermoelectric material.