Thermoelectric properties of quaternary Heusler alloysFe2VAl1−xSix

Abstract

We report the effects of Si substitution on the temperature-dependent electrical resistivity, Seebeck coefficient, as well as thermal conductivity in the Heusler-type compound ${\mathrm{Fe}}_{2}\mathrm{VAl}$. It is found that the substitution of Si onto the Al sites causes a significant decrease in the electrical resistivity and lattice thermal conductivity. A theoretical analysis indicated that the reduction of lattice thermal conductivity arises mainly from point-defect scattering of the phonons. With slight substitution, the Seebeck coefficient changes sign from positive to negative, accompanied by the appearance of a broad minimum at high temperatures. These features are associated with the change in the electronic band structure, where the Fermi level shifts upwards from the center of the pseudogap due to electron-doping effect. For $xg0.1$ in ${\mathrm{Fe}}_{2}{\mathrm{VAl}}_{1\ensuremath{-}x}{\mathrm{Si}}_{x}$, no broad minimum in the Seebeck coefficient appears, indicative of a dramatic modification in the band structure of these materials. While the thermoelectric performance improves with increasing Si concentration, the largest figure-of-merit $ZT$ value among these alloys is still an order of magnitude lower than conventional thermoelectric materials.