Previous studies have revealed that both Bi doping and Bi2Te3 alloying are successful strategies to optimize the thermoelectric performance of SnTe; however, detailed and thorough investigations on exactly how they differ in modulating the band structure and microstructure were seldom given. Through a systematic comparison between Bi-doped and Bi2Te3-alloyed SnTe, we find in this work that despite the fact that they both contribute to the valence band convergence of SnTe, Bi2Te3 alloying induces little effect on the hole concentration unlike the typical n-type feature of Bi-doping; moreover, Bi2Te3 alloying tends to produce dense dislocation arrays at micron-scale grain boundaries which differs significantly from the substitutional point defect character upon Bi-doping. It was then found that Bi2Te3 alloying exhibits a relatively higher quality factor (B ∼ μw/κlat) at higher temperatures than Bi-doping. Subsequent Ge-doping in Bi2Te3-alloyed samples results in further valence band convergence and hole concentration optimization and eventually results in a maximum figure of merit ZT of 1.4 at 873 K in the composition of (Sn0.88Ge0.12Te)0.97-(BiTe1.5)0.03.
Abubakar Yakubu Haruna,Yubo Luo,Wang Li,Zheng Ma,Tian Xu,Qinghui Jiang,Junyou Yang
Bismuth telluride-based (Bi2Te3) alloys have long been considered the best thermoelectric (TE) materials at room temperature. However, the n-type Bi2Te3 alloys always exhibit poor thermoelectric performance than their p-type counterpart, which severely limits the energy conversion efficiency of thermoelectric devices. Here, we demonstrate that incorporating AgBiSe2 can concurrently regulate the electrical and thermal transport properties as well as improve the mechanical performance of n-type Bi2Te2.69Se0.33Cl0.03 for high thermoelectric performance. Among these, AgBiSe2 effectively enhanced the Seebeck coefficients of n-type Bi2Te2.69Se0.33Cl0.03 due to the reduced carrier concentration and reduced the thermal conductivity of n-type Bi2Te2.69Se0.33Cl0.03 owing to the enhanced phonon scattering by AgBiSe2 as well as its low thermal conductivity nature. Consequently, the simultaneous optimization of electrical and thermal transport properties enables us to achieve a maximum ZT of ∼1.21 (at ∼353 K) and an average ZTave of ∼1.07 (300–433 K) for 3.5 wt % AgBiSe2-incorporated Bi2Te2.69Se0.33Cl0.03, which are ∼25.62 and ∼23.36% larger than those of Bi2Te2.69Se0.33Cl0.03, respectively. This work proves that the incorporation of AgBiSe2 is an efficient way to improve the thermoelectric performance of bismuth telluride-based materials.
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