Ni substitution improves the high-temperature thermoelectric performance of electronegative element Se-filled skutterudite Se_0.05Ni_xCo_4-xSb₁₂

The electronegative element-filled skutterudite (EN-SKD) has become an interesting thermoelectric material in the mid-temperature region in recent years. However, the strong intrinsic excitation above ~650 K affects its thermoelectric performance, limiting the practical applications in thermoelectric generators (TEG). To alleviate this situation, a series of EN-SKD compounds with different Ni substitutions, Se_0.05Ni_xCo_4-xSb₁₂ (x = 0.1, 0.2, 0.3, 0.4) are fabricated by solid-state reaction. It is found that the substitution of Ni for Co significantly suppresses the bipolar effect as the temperature above ~700 K due to the increase of electron concentration, reduces the lattice thermal conductivity (κ_L) by introducing phonon scattering centers, and consequently performs a significant enhancement of zT. Se_0.05Ni_0.4Co_3.6Sb₁₂ realizes a zT value two times higher than Se_0.05Ni_0.1Co_3.9Sb₁₂ at 823 K. This work demonstrates an approach to optimize thermoelectric performance by Ni substitution at Co sites in EN-SKD through the suppression of the bipolar effect on S and κ.