The effects of P substitution for Si as an n-type dopant on the thermoelectric properties of hot-pressed β-FeSi_(2) were investigated. The Seebeck coefficient, electrical resistivity, and thermal conductivity of the FeSi_(2-x)P_(x) 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 FeSi_(2-x)P_(x) 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 Fe_(0.98)Co_(0.02)Si_(2) 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-FeSi_(2), and a high thermoelectric performance, almost the same as that of the conventional Fe_(0.98)Co_(0.02)Si_(2), was obtained by P doping into β-FeSi_(2).
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