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

Abstract

A thermoelectric generator, as a solid-state device, is considered a potential candidate for recovering waste heat directly as electrical energy without any moving parts. However, thermoelectric materials limit the application of thermoelectric devices due to their high costs. Therefore, in this work, we attempt to improve the thermoelectric properties of a low-cost material, iron silicide, by optimizing the Ni doping level. The influence of Ni substitution on the structure and electrical and thermoelectric characteristics of bulk β-FexNi1−xSi2 (0 ≤ x ≤ 0.03) prepared by the conventional arc-melting method is investigated. The thermoelectric properties are reported over the temperature range of 80–800 K. At high temperatures, the Seebeck coefficients of Ni-substituted materials are higher and more uniform than that of the pristine material as a result of the reduced bipolar effect. The electrical resistivity decreases with increasing x owing to the increases in metallic ε-phase and carrier density. The ε-phase increases with Ni substitution, and solid solution limits of Ni in β-FeSi2 can be lower than 1%. The highest power factor of 200 μWm−1K−2 at 600 K is obtained for x = 0.001, resulting in the enhanced ZT value of 0.019 at 600 K.

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

“…6(b) shows that the m H of the 0.005 r x r 0.03 samples were 7 times higher than that of the x = 0 sample. This increase in m H is probably because of the lighter effective mass (m*) of Ni than that of Co. 39,40 As seen in Table 1, from x = 0.005 to x = 0.03, the m H ranged from 25(5) to 24(3) cm 2 V À1 s À1 , respectively. These m H values are about 80 times higher than that of ruthenium (Ru)-alloyed Co-doped b-FeSi 2 prepared by spark plasma sintering, 25 50 times higher than that of Co-or Ni-doped b-FeSi 2 prepared by pressure sintering, 33 and 4 times higher than that of the Co-doped b-FeSi 2 single crystal fabricated by the chemical vapor transport method.…”

“…This tendency is similar to that observed in a previous report when Ni alone is added to the b-FeSi 2 system. 40 Moreover, the pore size became larger after the heat treatment process. An increase in pore size is usually observed when phase changes occur during the heat treatment process because the volume of b-FeSi 2 differs from those of a-Fe 2 Si 5 and e-FeSi (3b-FeSi 2 ' a-Fe 2 Si 5 + e-FeSi).…”

“…39 Interestingly, it has been reported that the tendency of ρ of Ni-doped β-Fe 1− x Ni x Si 2 decreases with increasing temperature probably due to the higher μ H in the range of 10–35 cm 2 V −1 s −1 . 40 Since we have previously found that the maximum ZT was obtained in the β-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 β-Fe 0.97 Co 0.03 Si 2 prepared by the same fabrication process by alloying it with Ni in this work. When an appropriate amount of Ni is added to β-Fe 0.97 Co 0.03 Si 2 , the μ H is expected to increase.…”