Thermoelectric Properties of Fe2VAl and Fe2V0.75M0.25Al (M = Mo, Nb, Ta) Alloys: First-Principles Calculations

Ab initio investigations of the structural, electronic, and thermoelectric properties of stoichiometric Fe2VAl full-Heusler alloy and Fe2V0.75M0.25Al (M = Mo, Nb, Ta) nonstoichiometric alloys have been performed using density functional theory on the basis of the full-potential linearized augmented plane wave method with the generalized gradient approximation. The thermoelectric properties are calculated using semiclassical Boltzmann transport theory within the constant-relaxation-time approximation. Fe2VAl, Fe2V0.75Nb0.25Al, and Fe2V0.75Ta0.25Al alloys are found to exhibit a semimetallic behavior, while Fe2V0.75Mo0.25Al acts as a metal. We found that Fe2VAl has a pseudogap of about −0.13 eV, whereas Fe2V0.75Nb0.25Al and Fe2V0.75Ta0.25Al are characterized by a zero energy gap around the Fermi level. Thermoelectric calculations showed that Fe2VAl has both p- and n-type thermoelectric properties, where the p-type thermopower values are found to be higher than those of n-type. The Seebeck coefficient S has maximum values from 20 μV K−1 to 125 μV K−1 and from 19 μV K−1 to 90 μV K−1 in the temperature range of 100 K to 800 K for p- and n-type, respectively. The maximum thermoelectric properties can be obtained at carrier concentration of the order of 1020 cm−3 for p- or n-type doping. Substitution of Nb and Ta atoms enhanced the thermoelectric properties to 150 μV K−1 at 800 K. The optimum concentrations for the three partially substituted alloys were found to be between 1020 cm−3 and 1021 cm−3.