Enhanced High-Temperature Thermoelectric Performance of Yb₄Sb₃ via Ce/Bi Co-doping and Metallic Contact Deposition for Device Integration

Thermoelectrics (TE) for very high temperatures (>800 K) have numerous potential applications in heavy industry and space exploration. This article focuses on the compound Yb₄Sb₃ which is a promising p-type counterpart to the structurally related and high-performance n-type RE₃Te₄ (RE = Nd, La, Pr) for the fabrication of high-temperature TE modules. A quick and efficient method for synthesizing pure and fully dense Yb₄Sb₃ samples was developed and optimized using high-energy ball milling followed by reactive spark plasma sintering. The technique was utilized to produce a series of doubly doped Ce_xYb_4-xBi_0.2Sb_2.8 compounds. X-ray diffraction and scanning electron microscopy (SEM) were employed to establish the solubility limit of Ce, which was determined to be x = 0.4. TE properties of Yb₄Sb₃ and Ce_0.4Yb_3.6Bi_0.2Sb_2.8 were measured up to 1273 K, revealing that the doping strategy was effective in reducing the charge carrier concentration and thermal conductivity. This led to a significant increase in the TE figure-of-merit zT from 0.2 to 0.4 at 1273 K. In addition, screening of metallic contacts was conducted for the development of a thermoelectric module with Yb₄Sb₃. The results showed that two robust TE legs with Ni and Cu contacts were successfully produced through spark plasma sintering. The measured electric contact resistances were very promising, with average values of 2 and 1 μΩ cm² for Ni and Cu contacts, respectively.