Improved thermoelectric performance of Co-doped β-FeSi2 by Ni substitution

Abstract

Employing thermoelectric (TE) materials, which can directly convert heat into electricity, are a promising strategy for recovering industrial waste heat. Currently, TE materials with an acceptable conversion performance are expensive and toxic. Therefore, this work aims to enhance the TE performance of inexpensive and eco-friendly Co-doped iron silicide compounds by Ni addition. The investigation of the structural, electrical, and TE characteristics of Ni-alloyed β-Fe_0.97−xNi_xCo_0.03Si₂ (x = 0, 0.005, 0.01, 0.02, and 0.03) fabricated by the arc-melting process is reported in this study. The results show that the metallic ε-phase increased with x, resulting in a decrease in the solubility of the Ni and Co alloy material. However, the mobility (μ_H) significantly improved from 3.5(6) up to 25(5) cm² V⁻¹ s⁻¹ with Ni substitution, which is 7 times higher than the x = 0 sample. At high temperatures, the electrical resistivity of the Ni-substituted samples was remarkably lower than that of the x = 0 sample owing to the enhancement of μ_H. The presence of the ε-phase induced a negative impact on the Seebeck coefficient, and the thermal conductivity slightly decreased with x because of the increase in porosity. As a result, the optimum condition to improve the power factor and dimensionless figure of merit was achieved in the x = 0.01 sample with the maximum PF_max of 2400 μW m⁻¹ K⁻² and ZT_max of 0.31, indicating a three-fold enhancement compared with the x = 0 sample.