Thermoelectric properties of the Heusler-type Fe2VTaxAl1−x alloys

This study focuses on the thermoelectric properties of the Heusler-type Fe2VTaxAl1−x alloys (0≤x≤0.12). By means of Rietveld analyses on synchrotron X-ray diffraction patterns, it is shown that the Ta atoms enter sites occupied by V atoms in the stoichiometric Fe2VAl alloy, while the ejected V atoms are transferred to the vacant Al sites. This Ta substitution leads to an improvement of the n-type thermoelectric properties owing to two mechanisms. On the one hand, the atoms position in the structure leads to an off-stoichiometric effect such as already observed in V-rich Fe2V1+yAl1−y compounds: the Seebeck coefficient is increased towards negative absolute values and the electrical resistivity is decreased, with a large shift of their peak temperature towards higher temperature. The maximum power factor is 6.5 × 10−3 W/mK2 for x = 0.05 at 340 K. On the other hand, the heavy element Ta substitution combined with this off-stoichiometric effect leads to a large decrease of the thermal conductivity, owing to an increase of the scattering events. Consequently, the dimensionless figure of merit is seen to reach higher values than for the Fe2V1+yAl1−y alloys, i.e., 0.21–0.22 around 400–500 K for x = 0.05 and 500 K for x = 0.08