Improving thermoelectric performance of TiNiSn by mixing MnNiSb in the half-Heusler structure

TL;DR

This study enhances the thermoelectric performance of TiNiSn by partial substitution with MnNiSb, leading to a 61% increase in the figure of merit, through detailed analysis of phase composition and transport properties.

Contribution

It introduces a novel doping strategy with MnNiSb in TiNiSn to significantly improve thermoelectric efficiency and explores the resulting phase behavior and transport mechanisms.

Findings

ZT increased by 61% at x=0.05 doping level

Samples show transition from activated to metallic conduction with doping

Phase analysis reveals minor phases and defect-induced metallic behavior

Abstract

The thermoelectric properties of n type semiconductor, TiNiSn is optimized by partial substitution with metallic, MnNiSb in the half Heusler structure. Herein, we study the transport properties and intrinsic phase separation in the system. The Ti1-xMnxNiSn1-xSbx alloys were prepared by arc-melting and were annealed at temperatures obtained from differential thermal analysis and differential scanning calorimetry results. The phases were characterized using powder X-ray diffraction patterns, energy dispersive X-ray spectroscopy, and differential scanning calorimetry. After annealing the majority phase was TiNiSn with some Ni rich sites and the minority phases was majorly Ti6Sn5, Sn, and MnSn2. Ni rich sites were caused by Frenkel defects, this led to a metal-like behavior of the semiconducting specimens at low temperature. For x up to 0.05 the samples showed an activated conduction, whereas for x>0.05 they showed metallic character. The figure of merit for x=0.05 was increased by 61% (ZT=0.45) in comparison to the pure TiNiSn.