# Thermoelectric Properties of NbCoNixSn (x = 0–1)

## TL;DR

This study explores how adding nickel to the compound NbCoSn affects its thermoelectric performance, showing improved efficiency at specific doping levels.

## Contribution

The paper introduces Ni doping in NbCoSn and demonstrates its impact on thermoelectric properties through structural and electronic changes.

## Key findings

- Ni doping up to x = 0.05 enhances thermoelectric performance by forming interstitial solid solutions.
- Higher Ni content leads to the formation of full-Heusler secondary phases, altering the material's structure.
- The maximum ZT value of 0.52 at 975 K was achieved for NbCoNi0.05Sn.

## Abstract

The half-Heusler (HH) compound NbCoSn, with 18 valence electrons, is a promising thermoelectric (TE) material due to its favourable electrical properties and excellent thermal and chemical stability. Enhancing its TE performance typically involves doping and microstructure engineering. In this study, Ni was introduced into NbCoSn to form NbCoNixSn (x = 0–1), and the effects of Ni content on the microstructure and TE properties were systematically investigated. At low doping levels (x ≤ 0.05), Ni occupies interstitial sites, forming NbCoNixSn solid solutions. At higher concentrations (x > 0.05), full-Heusler (FH) secondary phases emerge, resulting in HH–FH composites. The introduction of Co/Ni interstitials enhances TE performance by creating in-gap electronic states and increasing phonon scattering through point defects. A clear structural transition from HH to FH phases is observed with increasing Ni content. The highest figure of merit, ZT ≈ 0.52 at 975 K, was obtained for NbCoNi0.05Sn, comparable to the best values reported for this system.