Enhanced thermoelectric performance of n-type Bi₂Te_2.7Se_0.3 by pyrite CoSe₂ addition

In this work, the thermoelectric (TE) performances of n-type Bi₂Te_2.7Se_0.3 with the addition of pyrite CoSe₂ were studied. The findings reveal an in-situ reaction between Bi₂Te_2.7Se_0.3 and CoSe₂ during the SPS process, resulting in the formation of a secondary phase, CoTe₂, which refined the microstructure of Bi₂Te_2.7Se_0.3. Consequently, the electrical conductivity and Seebeck coefficient of Bi₂Te_2.7Se_0.3 were simultaneously optimized, attaining a higher power factor of 30.2 μW cm⁻¹ K⁻² at room temperature. Additionally, due to the reduced average sound velocity and phonon mean free path, the lattice thermal conductivity of Bi₂Te_2.7Se_0.3 was suppressed by the incorporation of CoSe₂. Furthermore, the bipolar thermal conductivity also experienced slight suppression at elevated temperatures. Ultimately, a substantial figure of merit of 0.85 was achieved at 423 K for n-type Bi₂Te_2.7Se_0.3 with the addition of 3 mol% CoSe₂.