Enhancement of the thermoelectric properties in doped FeSb$_2$ bulk crystals

TL;DR

This study demonstrates that chemical doping, especially with Te, significantly reduces thermal conductivity in FeSb₂ crystals, enhancing their thermoelectric performance at cryogenic temperatures.

Contribution

It reveals how different dopants affect thermal conductivity and thermoelectric properties, highlighting Te doping's effectiveness in suppressing thermal conductivity while preserving thermoelectric efficiency.

Findings

Te doping reduces thermal conductivity from 250 to 8 W/Km

Cr and Co doping suppress thermal conductivity less effectively

Te doping maintains large Seebeck coefficient, improving ZT to ~0.05 at 100 K

Abstract

Kondo insulator FeSb$_2$ with large Seebeck coefficient would have potential in thermoelectric applications in cryogenic temperature range if it had not been for large thermal conductivity $\kappa$. Here we studied the influence of different chemical substitutions at Fe and Sb site on thermal conductivity and thermoelectric effect in high quality single crystals. At $5\%$ of Te doping at Sb site thermal conductivity is suppressed from $\sim 250$ W/Km in undoped sample to about 8 W/Km. However, Cr and Co doping at Fe site suppresses thermal conductivity more slowly than Te doping, and even at 20$\%$ Cr/Co doping the thermal conductivity remains $\sim 30$ W/Km. The analysis of different contributions to phonon scattering indicates that the giant suppression of $\kappa$ with Te is due to the enhanced point defect scattering originating from the strain field fluctuations. In contrast, Te-doping has small influence on the correlation effects and then for small Te substitution the large magnitude of the Seebeck coefficient is still preserved, leading to the enhanced thermoelectric figure of merit ($ZT\sim 0.05$ at $\sim 100$ K) in Fe(Sb$_{0.9}$Te$_{0.1}$)$_2$.