Optimization of Co additive amount to improve thermoelectric properties of β-FeSi₂

Abstract

The present manuscript deals with the synthesis of pure and Co-doped β-FeSi2 by conventional arc-melting method and the investigation of the effect of Co-dopant on the structural, electrical, and thermoelectric properties of β-Fe1-xCoxSi2 (0 ≤ x ≤ 0.06) from 300 to 800 K. The electrical resistivity decreases with increasing Co-doping due to the increase in carrier concentration. The Seebeck coefficient of all Co-doping samples (0.005 ≤ x ≤ 0.06) is higher and more stable than that of x = 0 due to the absence of the bipolar effect. Therefore, the maximum power factor is around 900 μWm-1K-2 obtained in x = 0.03 from 720 to 800 K. The thermal conductivity also slightly decreases with increasing x. As a result, the optimum doping level is achieved in x = 0.03 with the carrier density around 1.2(4) × 1020 cm-3 and mobility for 3.5(6) cm2V-1s-1, where the highest ZT is 0.099.

Effect of Ni Substitution on Thermoelectric Properties of Bulk β-Fe1−xNixSi2 (0 ≤ x ≤ 0.03)

“…It is considered that both Fe1 and Fe2 are slightly changed with Ni addition. Therefore, the Ni population should equally occupy both Fe1 and Fe2 sites, which is similar to a previous study wherein Co was doped into the β-FeSi2 system [20,34]. Figure 4d shows the reliability factor Rwp with x dependences.…”

“…This result suggests that the proposed arc-melting and direct-heat-treatment method is efficient at fabricating a high-relative-density sample that contributes positively to the decrease in electrical resistivity, which is good for TE application. The three dimensions of the orthorhombic crystal structure of β-FeSi 2 were provided by our previous report [20].…”

“…This result suggests that the proposed arc-melting and direct-heat-treatment method is efficient at fabricating a high-relative-density sample that contributes positively to the decrease in electrical resistivity, which is good for TE application. The three dimensions of the orthorhombic crystal structure of β-FeSi2 were provided by our previous report [20]. The bonds of the Fe1 and sites are formed geometrically in eight coordinates, four each to Si1 and Si2, and the bonds of Fe-Si vary in length from 2.361(5) to 2.402(6) Å and from 2.282(5) to 2.415(4) Å, respectively.…”

“…As a result, the ZT can be significantly improved due to the monotonicity in |S| and the decrease in ρ. Theoretically, it was reported that the optimum n H to improve the TE performance of β-FeSi 2 is approximately within the range of 1 × 10 20 to 2 × 10 21 cm −3 [15]. In fact, we prepared β-Fe 0.97 Co 0.03 Si 2 with the arc melting method and found a ZT value of 0.099 at 800 K [20]. Furthermore, many previous works [21][22][23][24][25][26][27][28][29][30] attempted to enhance the n H of β-FeSi 2 via doping with various impurities.…”

Improved thermoelectric performance of Co-doped β-FeSi2by Ni substitution

“…However, the tendency of r of this Co-doped sample was uniform over the temperature range of 300-800 K. This is probably due to the low mobility (m H ) of around 3.5 cm 2 V À1 s À1 . 39 Interestingly, it has been reported that the tendency of r of Ni-doped b-Fe 1Àx Ni x Si 2 decreases with increasing temperature probably due to the higher m H in the range of 10-35 cm 2 V À1 s À1 . 40 Since we have previously found that the maximum ZT was obtained in the b-Fe 0.97 Co 0.03 Si 2 matrix prepared by arc-melting followed by a heat treatment process, 39 we attempt to improve the performance of b-Fe 0.97 Co 0.03 Si 2 prepared by the same fabrication process by alloying it with Ni in this work.…”