Doping effects on thermoelectric properties of the off-stoichiometric Heusler compounds Fe2–xV1+xAl.

The thermoelectric properties of Heusler-type Fe2–xV1+xAl1–ySiy and Fe2–xV1+x–yTiyAl alloys have been investigated to clarify which off-stoichiometric alloy, i.e., V-rich (x>0) or V-poor (x<0), is more effective in enhancing the Seebeck coefficient when doped by Si and Ti, while retaining a low electrical resistivity. Large Seebeck coefficients of –182 μV/K and 110 μV/K at 300K are obtained for n-type Fe1.95V1.05Al0.97Si0.03 and p-type Fe2.04V0.93Ti0.03Al, respectively. When the Seebeck coefficient is plotted as a function of valence electron concentration (VEC), the VEC dependence for the doped off-stoichiometric alloys falls on characteristic curves depending on the off-stoichiometric composition x. It is concluded that a larger Seebeck coefficient with a negative sign can be obtained for the V-rich alloys rather than the V-poor alloys, whilst good p-type materials are always derived from the V-poor alloys. Substantial enhancements in the Seebeck coefficient for the off-stoichiometric alloys could be achieved by a favorable modification in the electronic structure around the Fermi level through the antisite V or Fe defect formation. [ABSTRACT FROM AUTHOR]