Doping effect of metal into iron disilicide on electronic structures and thermoelectric properties

Doping effects of elements into FeSi/sub 2/ on the electronic structures were studied relating to the thermoelectric properties. The studied elements were the metals possessing d- or f-electrons such as Mn, Co, Zn and Hf, W, os (f/sup 14/ series) and Nd, Eu and Yb in the lanthanide series, although only Yb, Hf and Os are reported here. The calculation was performed using the discrete variational X/spl alpha/ molecular orbital method. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) relates to electrical conductivity, and the Seebeck coefficient associated with the gap between HOMO and LUMO levels possessing the same symmetry which were degenerate. In experiment, doping with Yb/sub 2/O/sub 3/ increased the Seebeck coefficient and electrical resistivity did not change much, resulting in an improvement as large as twice the figure of merit for thermoelectricity.