Stoichiometric and off-stoichiometric full Heusler Fe2V1−xWxAl thermoelectric systems

A series of full Heusler alloys, ${\text{Fe}}_{2}{\text{V}}_{1\ensuremath{-}x}{\text{W}}_{x}\text{Al}$, $0\ensuremath{\le}x\ensuremath{\le}0.2$, was prepared and characterized, and relevant physical properties to account for the thermoelectric performance were studied in a wide temperature range. Additionally, off-stoichiometric samples with similar compositions have been included, and a 10% improvement of the thermoelectric figure of merit was obtained. The V/W substitution causes (i) a change of the main carrier type, from holes to electrons as evidenced from Seebeck and Hall measurements, and (ii) a substantial reduction of the lattice thermal conductivity due to a creation of lattice disorder by means of a distinct different mass and metallic radius upon the V/W substitution. Moreover $ZT$ values above 0.2 have been obtained. A microscopic understanding of the experimental data observed is revealed from ab initio calculations of the electronic and phononic structure. This series of alloys constitutes the basis for thin film systems, which have recently been found to exhibit $ZT$ values beyond those reported so far in the literature.