Manipal Journal of Science and Technology


The effects of Ge partial substitution on the Si site of FeSi Kondo insulator (KI) were investigated by means of electrical and thermal transport measurements. Electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (k) measurements were performed on a series of FeSi1-xGex alloys with x varying from 0.00 to 0.25. It is found that the substitution of Ge onto the Si sites causes a substantial decrease in the electrical resistivity and Seebeck coefficient at low temperatures, attributed to the shift of Fermi energy from the dip of the density of states as a consequence of the Ge substitution. The resistivity data between 100 and 250 K roughly obey an activated behavior and the transport gap (Δ) for this series of alloys was estimated from the lnρ vs 1/T plot. The stoichiometric FeSi has a giant peak in S (T) at T = 50 K, which was found to be suppressed on Ge substitution. Such observations in S (T) have been associated with formation of a charge gap and are in agreement with theoretical predications for Kondo insulators. A theoretical analysis of thermal conductivity indicates that the lattice phonons are responsible for the heat conduction and various thermal scattering mechanisms provide a reasonable explanation for the observed low-T maximum in k(T).

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