Effects of P doping on the thermoelectric properties of β-FeSi2

Abstract

The effects of P substitution for Si as an n-type dopant on the thermoelectric properties of hot-pressed β-FeSi2 were investigated. The Seebeck coefficient, electrical resistivity, and thermal conductivity of the FeSi2−xPx were measured from room temperature to 1100 K, and then the power factor and figure of merit were evaluated. The Seebeck coefficient of the hot-pressed FeSi2−xPx was negative, indicating that P atoms were definitely substituted for Si atoms as an n-type dopant in the β phase. The samples with x=0.02 and 0.04 had a Seebeck coefficient greater than that of the conventional hot-pressed Fe0.98Co0.02Si2 below 800 K. The electrical resistivity was significantly reduced by P doping, especially in the lower temperature range, and slightly decreased with increasing P content. The log ρ−1/T plots of the P-doped samples exhibited a specific behavior below 480 K, which was not observed in the case of the nondoped sample. The thermal conductivity of the P-doped sample was smaller than that of the nondoped sample in spite of the larger amount of the metallic ε phase. The figure of merit was significantly enhanced by P doping as compared with that of the nondoped β-FeSi2, and a high thermoelectric performance, almost the same as that of the conventional Fe0.98Co0.02Si2, was obtained by P doping into β-FeSi2.

Thermoelectric properties of hot-pressed Al- and Co-doped iron disilicide materials

“…The E g values at high temperature range for intrinsic conductive region are 0.60 and 0.56 eV for Al-and Co-doped samples. Compared to the energy gap of non-doped ␤-FeSi 2 , 0.90 eV [11], the values of E g for Al-and Co-doped FeSi 2 are low. It was reported that the energy gap was reduced when a ptype dopant, such as Mn, Nb, or Zr, or a n-type dopant, such as P, was added in FeSi 2 , which expanded the width of the valence band [11].…”

“…The main parameter required to improve for ␤-FeSi 2 is the ratio of electrical conductivity to thermal conductivity, if a high figure of merit is expected to achieve [5,7]. ␤-FeSi 2 is an intrinsic semiconductor, and some doping elements [4,[9][10][11][12] were added to form p-or n-type semiconductor to increase its electrical conductivity. The microstructural properties (grain size and porosity) of the material also have the influence on materials thermoelectric properties.…”

Influence of nitrogenizing and Al-doping on microstructures and thermoelectric properties of iron disilicide materials

“…Efforts to improve the thermoelectric properties of p-type FeSi 2 have been made by doping with Mn, Al, Cr, and Zr [8][9][10][11]. Ito et al managed to obtain p-type FeSi 2 with high thermoelectric performance comparable to that of the conventional Fe 0.98 Co 0.02 Si 2 by doping FeSi 2 with phosphorus [12].…”

Synthesis of Thermoelectric Fe<SUB>0.98</SUB>Co<SUB>0.02</SUB>Si<SUB>2</SUB> with Fine Ag Dispersion by Mechanical Milling with AgO Powder

“…1,2) The performance of a thermoelectric material is generally evaluated by the dimensionless figure of merit, ZT, which is calculated from the Seebeck coefficient, S, electrical resistivity, , thermal conductivity, , and the absolute temperature, T, in the equation ZT ¼ S 2 T=. In order to improve the electrical properties of the -FeSi 2 , such as Seebeck coefficient and electrical resistivity, the doping of various elements, Co, [3][4][5][6][7][8][9] Cr, 8) Ni, 8,9) Mn, 8,[10][11][12] Al, 3,4,6,12) Cu, 13) B, 14) Nb, 15) Zr, 16) or P, 17) etc., has been attempted during sample preparation. Co and Mn are well known as good dopants for n-type and p-type -FeSi 2 materials, respectively.…”