Integration of multi-scale defects for optimizing thermoelectric properties of n-type Cu_1-xCd_xFeS₂ (x = 0-0.1)

The performance of thermoelectric (TE) materials is strongly influenced by multi-scale defects. Some defects can improve the TE performance but some are unfavorable. Therefore, the multi-scale defects need to be integrated rationally to enhance the TE properties. Here, the defects including atomic-scale point defects, high-density grain boundaries and nano-precipitates were integrated into CuFeS₂, an n-type and Earth-abundant TE material. Primitively, a Cd dopant with high scattering factor was introduced to form point defects in Cu_1-xCd_xFeS₂ (x = 0-0.1) according to the calculated scattering parameters. Furthermore, the processes of quenching, annealing, high-energy ball milling (QAH) and sintering were carried out to integrate the multi-scale defects into Cu_1-xCd_xFeS₂. The results suggested that point defects and antisite defects were achieved and the unfavorable Cd'_Fe defects were suppressed effectively, leading to a higher electrical conductivity. Moreover, the CdS nano-precipitates played a vital role in carrier filtering to increase the Seebeck coefficient. Meanwhile, the high-density grain boundaries suppressed the lattice thermal conductivity. As a result, a peak ZT value of 0.39 at 723 K was obtained in Cu_0.92Cd_0.08FeS₂, which is the highest value reported so far in the CuFeS₂ family.