Study On The CoSb₃-based Thermoelectric Element And Device By Brazing

Co Sb3-based Filled skutterudite is regarded as a promising candidate for thermoelectric generator applications in the intermediate temperature range. Recently, the reported maximum ZT values have reached 1.7 for N-type Co Sb3-based skutterudite and 1.0 for P-type material. So far, few studies have been reported on Co Sb3-based skutterudite device. A reliable fabrication technique for Co Sb3-based skutterudite device is very important before applications of this kind of materials.In this work, the Co Sb3 material was successfully jointed with the electrode using the suitable middle layer. Reliability of the joints between electrode and skutterudite was evaluated systematically. We fabricated a 10 pairs device and studied its output characteristic. The following research work has been carried out in this study:(1) The barrier layer of Ti-Al and the contact layer of Ni are joined to filled skutterudite simultaneously by using spark plasma sintering(SPS) technique. The SEM shows that, an intermetallic compound(IMC) layer containing Al Co、Ti Co Sb and Ti Sb2 phases forms on the boundary between Yb0.3Co4Sb12 and Ti-Al; and for P type,the IMC contains Al(Co, Fe), Ti Sb2 and Ti2 Sb phases. The contact electrical resistivity of Ni/Ti-Al/ Yb0.3Co4Sb12 and Ni/Ti-Al/Ce Fe3 Co Sb12 are 3.8μ?·cm2 and 3.7μ?·cm2 respectively。(2) Mo-Cu alloy was used as electrode because its thermal expansion coefficient matches well with the Co Sb3 material. Ag-Cu-Zn solder was applied to connect electrode and P/N elements. The interfacial microstructure evolution and reliability of joints were investigated after thermal aging for 500℃.(3) After thermal aging at 500℃ for 30 days, the inter-diffusions at both Yb0.3Co4Sb12/Ti-Al interface and Ag-Cu-Zn/Ni interface tend to be steady, which thickness were about 30~40μm. The contact electrical resistivity of the Yb0.3Co4Sb12/Ti-Al/Ni/Ag-Cu-Zn/Mo-Cu thermoelectric joints maintained as lower than 10μ?·cm2 even after 30 days’ thermal aging.(4) For P-type, the inter-diffusions and micro cracks began to appear at Ce Fe3 Co Sb12/Ti-Al interface after 10 days, the cracks is more obvious with increasing the aging time. The contact electrical resistivity of Ce Fe3 Co Sb12/Ti-Al/Ni/Ag-Cu-Zn/Mo-Cu joints maintained more than 20μ?·cm2, but the diffusion between Ni/Ag-Cu-Zn is similar to the N-type element.(5) A 10 pairs of Co Sb3-based device was fabricated using brazing method, the device generated a maximum output power of 7.84 W and a maximum conversion efficiency of 6.2% under the thermal condition of hot side temperature Th=598 and a temperature difference ℃ΔT=566℃.