Thermoelectric Properties of Doped Iron Disilicide
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THERMOELECTRIC PROPERTIES OF DOPED IRON DISILICIDE Jun-ichi Tani, Hiroyasu Kido Department of Inorganic Chemistry, Osaka Municipal Technical Research Institute, 1-6-50 Morinomiya, Joto-ku, Osaka 536-8553, Japan, [email protected] ABSTRACT In order to investigate the thermoelectric properties of Re-doped β -FeSi2 (Fe1-xRexSi2), Ir-doped β -FeSi2 (Fe1-xIrxSi2), and Pt-doped β -FeSi2 (Fe1-xPtxSi2), the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of these samples have been measured in the temperature range between 300 and 1150 K. Fe1-xRexSi2 is p-type, while Fe1-xIrxSi2 and Fe1-xPt xSi2 are n-type over the measured temperature range. The solubility limits of dopant are estimated to be 0.2at% for Fe1-xRexSi2, 0.5at% for Fe1-xIrxSi2, and 1.9at% for Fe1-xPtxSi2. A maximum ZT value of 0.14 was obtained for Fe1-xPt xSi2 (x=0.03) at the temperature 847 K. INTRODUCTION The transition metal silicides are of broad interest from the viewpoint of their structural and functional applications. The semiconducting phase of iron disilicide (β -FeSi2) [1] has been studied as a candidate material for thermoelectric conversion application, because of its superior features such as a large Seebeck coefficient, low electrical resistivity, and chemical stability [2-5]. There have been many attempts to dope some additives into β -FeSi2 to alter its semiconducting properties. The conduction types are p-type, produced by doping with V, Cr, Mn, and Al; and n-type, produced by doping with Co, Ni, Pt, and Pd [2-9]. Komabayashi et.al. [9] reported the electrical resistivity and Seebeck coefficient of Pt-doped β -FeSi2 film at room temperature. They concluded that Pt is superior to Co as an additive for n-type β -FeSi2 from the results of the power factor measurement. Desirable qualities for thermoelectric materials include a large Seebeck coefficient S, a large electrical resistivity ρ, and a small thermal conductivity κ. These quantities determine the so-called thermoelectric figure of merit, Z=S2/ρκ. However, to our knowledge, there has been no investigation concerning the thermal conductivity and Hall effect of Fe1-xPtxSi2, and some of transport properties and figure of merit have not been determined. Re and Ir are also expected to be attractive dopants of β -FeSi2 because Re and Ir belong to VIIA and VIIIA group as the same as Mn and Co, which are well-known dopants of β -FeSi2. In addition, the atomic radii of Re and Ir are larger than those of Mn and Co. Therefore, it is expected to have lower thermal conductivity than Mn-doped and Co-doped β -FeSi2. However, there has no report concerning the thermoelectric properties of Re-doped and Ir-doped β -FeSi2. In this paper, the effects of doping on thermoelectric properties of β -FeSi2 have been systematically investigated using Re, Ir, and Pt as impurities in the temperature range between 300 and 1150 K. We also present data for nondoped β -FeSi2 for comparison. EXPERIMENT Powders of high purity, Fe (>99.9%), Si (>99.999%), Re (>99.9%), Ir (>99.9%), and Pt (
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