Entropy engineering stimulates the thermoelectric performance of FeCoNiAlSix high-entropy alloys

The present study explores the role of entropy engineering on thermoelectric properties of FeCoNiAlSix high entropy alloys (HEAs) as a function of Si content. The addition of Si content increased mixing entropy, and reduces valance electron concentration, leading to phase transition from dual FCC+BCC phase to single BCC phase. With increasing Si content, the Seebeck coefficient increases due to a reduction in carrier concentration and an increase in effective mass. The lowest lattice thermal conductivity of 1.202 W/m∙K was obtained at 700 K for the FeCoNiAlSi_0.6 HEA due to strong phonon scattering induced by lattice distortion. As a result, a maximum figure of merit, ZT ∼ 0.016 was achieved at 700 K for the FeCoNiAlSi_0.6 HEA. In addition, the hardness of HEAs effectively increased from 520±10 to 740±10 HV with Si content. Therefore, entropy engineering is found to be a promising method to enhance thermoelectric and mechanical performance as well.