Optimizing Electronic Quality Factor toward High‐Performance Ge_1−x−yTa_xSb_yTe Thermoelectrics: The Role of Transition Metal Doping

Abstract

Owing to high intrinsic figure‐of‐merit implemented by multi‐band valleytronics, GeTe‐based thermoelectric materials are promising for medium‐temperature applications. Transition metals are widely used as dopants for developing high‐performance GeTe thermoelectric materials. Herein, relevant work is critically reviewed to establish a correlation among transition metal doping, electronic quality factor, and figure‐of‐merit of GeTe. From first‐principle calculations, it is found that Ta, as an undiscovered dopant in GeTe, can effectively converge energy offset between light and heavy conduction band extrema to enhance effective mass at high temperature. Such manipulation is verified by the increased Seebeck coefficient of synthesized Ge1−x−yTaxSbyTe samples from 160 to 180 µV K−1 at 775 K upon doping Ta, then to 220 µV K−1 with further alloying Sb. Characterization using electron microscopy also reveals the unique herringbone structure associated with multi‐scale lattice defects induced by Ta doping, which greatly hinder phonon propagation to decrease thermal conductivity. As a result, a figure‐of‐merit of ≈2.0 is attained in the Ge0.88Ta0.02Sb0.10Te sample, reflecting a maximum heat‐to‐electricity efficiency up to 17.7% under a temperature gradient of 400 K. The rationalized beneficial effects stemming from Ta doping is an important observation that will stimulate new exploration toward high‐performance GeTe‐based thermoelectric materials.

Regulation of Ge vacancies through Sm doping resulting in superior thermoelectric performance in GeTe

“…At room temperature, the pristine GeTe exhibits a total thermal conductivity of 6.29 W m −1 K −1 , which is lower than previously reported values for GeTe based materials. 11,16,51,53,54 The total thermal conductivities of all samples exhibit a gradual decreasing trend with increase of temperature below 730 K. This is due to the decrease of both κ e and κ L . With increasing temperature, the electrical conductivity shows a monotonous decrease as shown in Fig.…”

“…The power factor of 5409 μW m −1 K −2 at 730 K in Ge 0.94 Sm 0.06 Te is a relatively high value compared with the previously reported results. 8,37,38,52–56 This is primarily ascribed to the high electrical conductivity, which remains at a high value of ∼2500 S cm −1 at 730 K for Ge 0.94 Sm 0.06 Te. The high electrical conductivity in our sample is owing to the high hole mobility (79.7 cm 2 V −1 s −1 measured at room temperature).…”

“…Generally the GeTe based materials prepared by the mechanical alloying method 8,43 exhibit lower thermal conductivity compared with those prepared by other methods such as vacuum melting. 11,16,51,53,54…”

Enhanced Thermoelectric Properties of Ti2FeNiSb2 Double Half‐Heusler Compound by Sn Doping

“…Tellurides (Bi 2 Te 3 , [ 8 ] GeTe [ 9 ] ) and selenides (Cu 2 Se, [ 10 ] SnSe [ 11 ] ) have been widely known as good TE materials owing to their high TE conversion efficiency. However, the mechanical and thermal stability of these materials is unsuitable for high‐temperature TE applications.…”

“…[5,6] In addition, exploring a new class of materials with phonon-glass and electron-crystal (PGEC) concept has been of immense interest in TE community. [7] Tellurides (Bi 2 Te 3 , [8] GeTe [9] ) and selenides (Cu 2 Se, [10] SnSe [11] ) have been widely known as good TE materials owing to their high TE conversion efficiency. However, the mechanical and thermal stability of these materials is unsuitable for hightemperature TE applications.…”