Synthesis and transport properties of M3 Ni3 Sb4 (M=Zr and Hf): An intermetallic semiconductor

The Seebeck coefficient, electrical resistivity, thermal conductivity, and Hall effect for the cubic phases M3 Ni3 Sb4 (M=Zr or Hf) have been measured. These materials were synthesized by induction melting of the constituent elements with subsequent annealing. Powder x-ray diffraction and electron probe microanalysis reveal that a single phase of the Y3 Au3 Sb4 structure type was obtained. The Seebeck coefficients of both Hf3 Ni3 Sb4 and Zr3 Ni3 Sb4 were found to be small, negative, and temperature independent below 150 K. Above this temperature a positive Seebeck coefficient is observed with a nearly linear temperature dependence. Modeling of the Hall coefficient and resistivity reveals that the transport properties of these materials can be explained using a two-band model of impurity conduction dominant at low temperatures and valence band conduction prevalent at temperatures above 150 K. Both compounds exhibit low thermal conductivity with values of 4.3 W/m-K and 2.7 W/m-K at room temperature for the Zr and Hf analogs, respectively. This may make these materials interesting for intermediate- to high-temperature thermoelectric applications. The effect of Sb deficiency on the thermoelectric properties is also investigated. Parallels in behavior between the title compounds and the half-Heuslers MNiSn (M=Zr and Hf) are observed and explained.