Thermal shock resistance and thermoelectric properties of boron doped iron disilicides

The phase analysis was carried out for the (1 -x) FeSi2 + xBSi(2) system in the composition range of 0 less than or equal to x less than or equal to 0.08 by an X-ray technique. It was found that B atoms in FeSi2 were substituted by Fe atoms and that a solid solution Fe1-xBxSi2 was formed in the composition range of x less than or equal to 0.03. The thermal shock resistance was estimated by the number of quenching cycle times, before crack was initiated by heating to 1073 K and subsequently water quenching to 300 K. For x = 0, a crack was initiated on the specimen surface with one quenching cycle, while no crack was found until forty quenching cycles for x = 0.03. The effect of B atoms on thermoelectric properties of the sintered (i -x) FeSi2 + xBSi(2) have been investigated at 300 K, and the thermoelectromotive force E-0 and effective mean resistivity r(e) were observed up to a temperature difference of 800 K. It was found that B atoms acted as the donors. The absolute value of the Seebeck coefficient at 300 K was 103.5 mu V K-1 for x = 0 and increased up to 681 mu V K-1 for x = 0.03. Lattice thermal conductivity at 300 K decreased with increasing x and the reduction ratio was 12% for x = 0.03. The effective maximum power P-e(= E-0(2)/4r(e)) of P-type FeSi2 doped with Mn and B was lower than that of Mn doped FeSi2, while P-e of n-type FeSi2 doped with Co and B was equivalent to that of un-doped B. A P-type or n-type thermoelectric material with a high thermal shock resistance was formed by double doping of FeSi2 with Mn and B or with Co and B, respectively.