Composition-induced metal-semiconductor-metal crossover in half-Heusler Fe1-xNixTiSb - art. no. 155103

Structural and electrical transport properties of half-Heusler Fe1-xNixTiSb solid solutions have been investigated using x-ray diffraction, Fe-57 Moss bauer spectroscopy, resistivity, and thermopower measurements. The electron ic structure of the compounds was studied using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA). The resistivity curves measured over the 80-800 K temperature range show a remarkable modification of rho (T) versus x in Fe1-xNixTiSb, i.e., a metalliclike character both in Fe-ric h (x = 0.25) and Ni-rich (x = 0.75) samples and a semiconductinglike behavi or near x = 0.5. Moreover, the room-temperature Seebeck coefficient S chang es from highly positive in Fe0.6Ni0.4TiSb to highly negative in Fe0.4Ni0.6T iSb, while S is near zero in the x = 0.25 and x = 0.75 compositions. Based on the KKR-CPA results, the electrical transport properties of Fe1-xNixTiSb arise from the appearance of an energy gap at the Fermi level for the x = 0.5 content. This electronic structure feature indicates that FeTiSb and Ni TiSb can be seen as one-hole and one-electron compounds, respectively, expl aining a change in sign of the Seebeck coefficient in disordered phases nea r x = 0.5.