Effects of Ge substitution on the thermoelectric properties and pseudogap characteristics ofFe2VGa

Abstract

We report the effects of partial substitution of Ge onto the Ga sites ofFe2VGa by measuring electrical resistivity, Seebeck coefficient and thermal conductivity as afunction of temperature. It is found that Ge substitution effectively dopes electrons to thesystem and thus causes a dramatic decrease in the electrical resistivity. The Seebeckcoefficient changes sign from positive to negative upon replacing Ga by Ge, which is ingood agreement with a simple band filling picture. In addition, the magnitudeof the Seebeck coefficient gradually increases and attains a maximum value of85 µV K−1 at around120 K for Fe2VGa0.9Ge0.1. Such a variation of Seebeck coefficient can be understood by means of rigidband-like shifting of the Fermi level across the pseudogap. The thermalconductivity is also reduced and a detailed analysis based on the Debyeapproximation indicates that the extrinsic disorder introduced by Ge substitution inFe2VGa has a minor contribution to the point defect scattering. Other lattice imperfections, such asantisite disorder, may be the main source for the point defect scattering whichshows no systematic variation with Ge concentration. While the thermoelectricperformance improves with the partial substitution of Ge, the largest figure-of-merit(ZT) value among these presently investigated alloys is still an order of magnitude lower thanthe conventional thermoelectric materials.