Effect of Bi-substitution on Structural Stability and Improved Thermoelectric Performance of p-type Half-Heusler TaSbRu: A First-principles Study

TL;DR

This study uses first-principles calculations to analyze how Bi-substitution affects the structural stability and thermoelectric performance of p-type TaSbRu, revealing significant improvements in ZT at high temperatures.

Contribution

It provides detailed insights into the effects of Bi-substitution on electronic structure, thermal conductivity, and thermoelectric efficiency of TaSbRu, considering critical parameters often neglected.

Findings

Bi-substitution reduces lattice thermal conductivity significantly.

ZT value increases to 1.1 at 1200 K with 50% Bi substitution.

Power factor slightly decreases with Bi substitution.

Abstract

Recently, Fang et al. have predicted a high ZT of 1.54 in TaSbRu alloys at 1200 K from first-principles without considering spin-orbit interaction, accurate electronic structure, details of phonon scattering, and energy-dependent holes relaxation time. Here, we report the details of structural stability and thermoelectric performance of Bi-Substituted p-type TaSbRu from first-principles calculations considering theses important parameters. This indirect bandgap semiconductor (Eg=0.8 eV by TB-mBJ+SOC) has highly dispersive and degenerate valence bands, which lead to a maximum power factor, 3.8 mWm-1K-2 at 300K. As Sb-5p has a small contribution to the bandgap formation, the substitution of Bi on the Sb site does not cause significant change to the electronic structure. Although the Seebeck coefficient increases by Bi due to slight changes in the bandgap, electrical conductivity, and hence, the power factor reduces to ~3 mW m-1K-2 at 300K (50% Bi). On the other side, lattice thermal conductivity drops effectively to 5 from 20 W/m K as Bi introduces a significant contribution in the acoustic phonon region and intensify phonon scattering. Thus, ZT value is improved through Bi-substitution, reaching 1.1 (50% Bi) at 1200 K from 0.45 (pure TaSbRu) only. Therefore, the present study suggests how to improve the TE performance of Sb-based half-Heusler compounds and TaSbRu (with 50% Bi) is a promising material for high-temperature applications.