Thermoelectric properties of the semimetallic Heusler compounds Fe_2-xV_1+xM (M = Al, Ga)

We have studied the thermoelectric properties of the stoichiometric and off-stoichiometric Heusler compounds Fe_2-xV_1+xM (M = Al, Ga) between 10 and 300 K. Seebeck coefficient (S) measurements indicate that stoichiometric Fe₂VAl and Fe₂VGa are p-type materials with moderate S values of about 30-40 μV/K at room temperature. Upon substituting the Fe site with V, a significant enhancement on Seebeck coefficients accompanied by a sign change are observed. On the other hand, the low-temperature resistivity (p) grows drastically with V substitution for Fe, while the thermal conductivity (κ) remains almost unaffected in the substitution levels we investigated. These features are consistent with other experimental results and are related to issues raised by band-structure calculations. The thermoelectric performance in these semimetallic Heusler compounds is estimated to be an order of magnitude lower than conventional thermoelectric materials.