Off-stoichiometry effect on the thermoelectric properties of the pseudogap Heusler compounds

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A combination of a large Seebeck coefficient and a low electrical resistivity has been obtained for the off-stoichiometric Fe2-xV1+xAl alloys owing to the doping of quaternary elements. On the basis of the valence electron concentration (VEC) dependence of the Seebeck coefficient, a large negative value of -180 microV/K can be obtained for the V-rich (x>0) alloys, whilst good p-type materials with 110 microV/K are derived from the Fe-rich (x<0) alloys. Because of the V/Al off-stoichiometry effect, a large Seebeck coefficient as well as a low electrical resistivity has also been found for Fe2V1+xAl1-x and Fe2VTaxAl1-x alloys, together with a large shift of their peak temperatures towards high temperatures of 400-600 K. The heavy element Ta doping combined with the off-stoichiometry effect leads to a significant decrease in the thermal conductivity, so that the dimensionless figure of merit reaches ZT=0.22 at around 400-500 K.