Doping Effects on Thermoelectric Properties of the Pseudogap Fe2VAl System

We report on the temperature dependence of electrical resistivity, Seebeck coefficient and Hall coefficient for Fe2(V1−yTiy)Al with y=0−0.25 and Fe2(V1−zMoz)Al with z=0−0.20. While the Heusler-type Fe2VAl (y=z=0) exhibits a semiconductor-like resistivity behavior, a slight substitution of Ti or Mo for V causes a sharp decrease in the low-temperature resistivity and a large enhancement in the Seebeck coefficient S: a sign of S is positive for the Ti substitution but negative for the Mo substitution. Substantial enhancements for the Seebeck coefficient are in reasonable accord with changes in the Hall coefficient and can be explained on the basis of the electronic structure of Fe2VAl, where the Fermi level is expected to shift slightly from the center of the pseudogap upon the substitution of Ti or Mo for V. In particular, the Mo substitution leads to a large power factor of 4×10−3 W/mK2 at room temperature, which is comparable to that of conventional thermoelectric materials.