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

TL;DR

This study synthesizes and characterizes five Ti-Ni-Sn based half-Heusler alloys, revealing their thermophysical and magnetic properties, including electrical resistivity, Seebeck coefficient, and magnetic behavior, with potential implications for thermoelectric applications.

Contribution

First comprehensive investigation of thermophysical and magnetic properties of p- and n-type Ti-Ni-Sn half-Heusler alloys across wide temperature ranges.

Findings

Alloys exhibit degenerate semiconductor behavior with resistivity 0.06-5 mΩ·cm.

p-type alloys show a transition from metallic to semiconducting behavior around 300-500 K.

n-type and compensated alloys display weak metallic behavior throughout the temperature range.

Abstract

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 to 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 to 5 m{\Omega} 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 to 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 microV K-1 while that of the n-type alloys increases continuously reaching a value of 45 microV K-1 at ~ 800 K. The corresponding power factor of the n-type alloy reaches 900 microW m-1 K-2 at ~ 900 K compared to a maximum of ~ 250 microW 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.