Thermophysical and magnetic properties of p- and n-type Ti-Ni-Sn based half-Heusler alloys

A total of 5 different half-Heusler alloys, two p-type and two n-type with the fifth a charge compensated alloy have been designed and synthesized. The thermophysical properties of these alloys have been investigated in the range 10 K-1000 K while the magnetic behavior has been studied up to 300 K. The electrical resistivity of all the alloys varies within the range 0.06-5 mΩ cm indicating that they are in the degenerate semiconductor limits. The temperature dependence of p-type alloys exhibits a transition from metallic to semiconducting behavior, typical of topological insulators. The transition is found to occur in the range 300 K-500 K. The n-type and compensated alloys exhibit a weak metallic behavior in the complete temperature range. The Seebeck coefficient in the p-type alloys increases with temperature reaching a maximum value of 50 μV K−1 while that of the n-type alloys increases continuously reaching a value of 45 μV K−1 at ∼800 K. The corresponding power factor of the n-type alloy reaches 900 μW m−1 K−2 at ∼900 K compared to a maximum of ∼250 μW m−1 K−2 at 700 K for the p-type alloy. Magnetically the p-type and n-type alloys are found to be paramagnetic while the compensated alloy exhibits a ferromagnetic behavior.