Thermoelectric properties of Heusler-type Ru₂VAl_1−xGa_x alloys

Electrical and thermal transport properties of the Heusler-type alloys, Ru₂VAl_1−xGa_x (x = 0.0–1.0) were studied by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements. All studied compounds show weak metallic characteristics with a low residual resistivity ratio. In addition, the Ru₂VAl_1−xGa_x alloys with x ≤ 0.75 show an n-type thermoelectric conduction from 10 to 300 K, while Ru₂VGa displays p-type conduction. The estimated Fermi energy of these materials is higher than 0.5 eV, endorsing their metallic character. From the thermal conductivity study, we noticed that low-temperature thermal conductivity decreases with increasing Ga content for x ≤ 0.5 and then increases with further Ga substitution. This observation is essentially due to the change in the phonon scattering processes as a result of the substitution of heavier Ga atoms into the Al sites of Ru₂VAl. It is important that an enhanced thermoelectric figure of merit ZT was found in Ru₂VAl_0.25Ga_0.75, about seven times higher than that in Ru₂VAl.