Electronic transport in Heusler-type Fe2VAl1-xMx alloys (M=B,In,Si)

The temperature variation of electrical resistivity rho(T) and Seebeck coefficient S(T) of Heusler-type Fe2VAl1-xBx (0 <= x <= 1) alloys have been investigated. All the studied alloys were crystallized into a single-phase cubic structure with Fm3m space group. The rho(T) shows a negative temperature coefficient of resistivity (TCR) for the x=0 sample, which turns into a positive TCR for the x=1 sample; while intermediate compositions show a resistivity minimum at low temperatures (T-min) below 50 K. From the analysis of temperature dependence of the electrical resistivity data, we demonstrate a semiconductorlike to metal transition on B substitution in the Fe2VAl alloy. With a minute substitution of isoelements (B and In) and nonisoelement (Si), S changes drastically in its sign and magnitude accompanied by an appearance of a broad maximum at higher temperatures, which shifts toward high temperatures with increasing concentration of the substituents. These features are indicative of a dramatic modification in the band structures of the Fe2VAl alloy with the substitution of elements. Although similar changes in rho and S values with compositions of B-, In-, and Si-substituted Fe2VAl alloys are observed, the rho decreases rapidly on B substitution and ultimately attains a metallic behavior, suggesting a true semiconductorlike to metal transition. The strong composition dependence of S and rho on elemental substitution is attributed to the size, relative positions of the atomic levels and the number of valence electrons of the substituents.