Contrasting roles of Bi-doping and Bi2Te3 alloying on the thermoelectric performance of SnTe†
Abstract
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.
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