Preparation and Thermoelectric Transport Properties of P-doped β-FeSi2
β-FeSi2,an environmentally friendly and high temperature oxidation-resistant thermoelectric material,has potential applications in the field of industrial waste heat recovery.Previous studies have shown that phosphorus(P),an ideal n-type dopant in the silicon(Si)site of β-FeSi2,can easily lead to the formation of a secondary phase,thereby limiting the enhancement of thermoelectric performance.In this study,a series of FeSi2-xPx(x=0,0.02,0.04,0.06)samples were synthesized using an induction melting method,which greatly inhibited the formation of the secondary phase.Then,the influence of P doping on the electrical and thermal transport properties of β-FeSi2 was studied.The results indicate that the solubility limit of P in β-FeSi2 is about 0.04,consistent with earlier theoretical predictions based on the defect formation energy.It is also discovered that P doping enhanced the thermoelectric performance of β-FeSi2,culminating in an optimal figure of merit(ZT)of FeSi1.96P0.04 approximately 0.12 at 850 K,which is much higher than the previous results(ZT about 0.03 at 673 K).However,compared to β-FeSi2 doped with other n-type elements like cobalt(Co)and iridium(Ir),which can achieve carrier concentrations up to 1022 cm-3,P-doped β-FeSi2 exhibits lower carrier concentrations,with the highest of only 1020 cm-3.This results in a weaker electron-phonon scattering effect,which in turn constrains the overall enhancement of the thermoelectric performance.If the carrier concentration could be further increased,the thermoelectric performance of the material is expected to evolve significantly.
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