Abstract
Lead-free and eco-friendly GeTe shows promising mid-temperature thermoelectric applications. However, a low Seebeck coefficient due to its intrinsically high hole concentration induced by Ge vacancies, and a relatively high thermal conductivity result in inferior thermoelectric performance in pristine GeTe. Extrinsic dopants such as Sb, Bi, and Y could play a crucial role in regulating the hole concentration of GeTe because of their different valence states as cations and high solubility in GeTe. Here we investigate the thermoelectric performance of GeTe upon Sb doping, and demonstrate a high maximum zT value up to 1.88 in Ge0.90Sb0.10Te as a result of the significant suppression in thermal conductivity while maintaining a high power factor. The maintained high power factor is due to the markable enhancement in the Seebeck coefficient, which could be attributed to the significant suppression of hole concentration and the valence band convergence upon Sb doping, while the low thermal conductivity stems from the suppression of electronic thermal conductivity due to the increase in electrical resistivity and the lowering of lattice thermal conductivity through strengthening the phonon scattering by lattice distortion, dislocations, and twin boundaries. The excellent thermoelectric performance of Ge0.90Sb0.10Te shows good reproducibility and thermal stability. This work confirms that Ge0.90Sb0.10Te is a superior thermoelectric material for practical application.
Highlights
Thermoelectric (TE) materials can convert heat directly into available electricity based on the Seebeck effect, providing an alternative way to utilize fossil energy more efficiently [1,2,3,4,5,6]
The thermoelectric material performance can be estimated by the dimensionless figure of merit zT = S2Tσ/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity, which usually stems from the crystal lattice vibrations and the charge carriers drift
We proved that a maximum zT of 1.88 at 773 K could be attained in Ge0.90Sb0.10Te with good reproducibility and thermal stability
Summary
Thermoelectric (TE) materials can convert heat directly into available electricity based on the Seebeck effect, providing an alternative way to utilize fossil energy more efficiently [1,2,3,4,5,6]. IV–VI semiconductors with a narrow band gap have made a great progress in terms of theory and TE performance, showing a bright prospect in TE application [7,8,9,10,11]. These compounds exhibit a unique TE-favorable property portfolio such as high valley degeneracy, large dielectric function, and strong lattice anharmonicity empowered by metavalent bonding [12]. Such features are beneficial to adequately optimize the electronic transport properties, and, in turn, yield a high zT, e.g., the maximum zT over 2 is attainable in (Bi, Cu), (Bi, Pb), (Sb, Pb), and (Sb, In) codoping systems [24,25,26,27,28]
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