High thermoelectric performance of p-BiSbTe compounds prepared by ultra-fast thermally induced reaction

The traditional zone melting (ZM) method for the fabrication of state of the art Bi2Te3-based thermoelectric materials has long been considered a time and energy intensive process. Herein, a combustion synthesis known as the thermally induced flash synthesis (TIFS) is employed to synthesize high performance p-type BiSbTe alloys within 20 min compared to tens of hours for the ZM samples. The thermodynamic parameters and phase transformation mechanism during the TIFS process were systematically studied for the first time. TIFS combined with plasma activated sintering (PAS) results in a single phase homogeneous material with excellent repeatability, high thermoelectric performance (maximum ZT ∼ 1.2 at 373 K) and robust mechanical properties in a very short time of less than 20 min. The technologically relevant average ZT value of TIFS-PAS fabricated Bi0.5Sb1.5Te3 from 298 K to 523 K is 0.86, about a 46% improvement over the ZM sample. The compressive and bending strength of TIFS-PAS Bi0.5Sb1.5Te3 are also improved by about 5 fold compared with those of the ZM samples. Thermoelectric power generation modules assembled using the TIFS-based high performance n and p type materials show the largest thermoelectric conversion efficiency of 5.2% when subjected to a temperature gradient of 250 K, representing about 42% enhancement compared with the commercial ZM-based module. Because of the simplicity and scalability of the process and short synthesis time, the TIFS-PAS technology provides a new and efficient way for large-scale, economical fabrication of Bi2Te3-based thermoelectrics.

Table S1.Fitting parameters for the heat capacity of Bi x Sb 2-x Te 3 (x=0.0~0.6)compounds.
Table S2.Performance parameters of the fabricated modules.

Figure S1 :
Figure S1: Schematic diagram of an apparatus to measure the temperature profile during the thermally induced flash synthesis

Figure S4 :
Figure S4: Back-scattered electron image of a polished surface of Bi 0.5 Sb 1.5 Te 3 processed by thermally induced flash synthesis at 823 K for 3 min.Insets show elemental distributions.

Figure S6 :
Figure S6: XRD patterns of Bi 0.5 Sb 1.5 Te 3 after thermally induced flash synthesis at 823 K for 2 min and 3 min duration.The inset is an expanded view of the 2 interval between 27 0 and 29 0 .

Figure S8 :
Figure S8: Heat flow curve of Bi 0.5 Sb 1.5 Te 3 showing signatures of the presence of Bi, Sb and Te at different temperatures (the upper peak and valley are corresponding to exothermic and endothermic process respectively.):(a) Temperature range of 500 K~850 K; (b) Detailed view of the 800 K ~825 K range.

Figure S10 :
Figure S10: Room temperature Seebeck coefficient of Bi x Sb 2-x Te 3 samples synthesized by TIFS-PAS and plotted as a function of the carrier concentration (the Pisarenko plot)

Figure
Figure S12: (a) Bipolar thermal conductivity of Bi 0.5 Sb 1.5 Te 3 synthesized by TIFS-PAS; (b) Temperature dependence of the bipolar thermal conductivity of Bi x Sb 2-x Te 3 synthesized by TIFS-PAS.

Figure
Figure S15: (a) and (b) Image of Modules (30×30×3.8mm 3 ) assembled from TIFS-PAS thermoelectric materials and Zone Melting ingots (ZM) with a total of 71 pairs of n-p Bi 2 Te 3 based materials for each module.

Figure S16 :
Figure S16: The output performance of a commercial module fabricated by using Zone Melting ingot materials.

Figure S17 :
Figure S17: The output performance of a module fabricated from TIFS-PASprocessed materials.
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