Screening of half-Heuslers with temperature-induced band convergence and enhanced thermoelectric properties

TL;DR

This study reveals the importance of temperature-induced band convergence in half-Heusler thermoelectric materials, using electron-phonon renormalization to identify promising compounds with enhanced Seebeck coefficients.

Contribution

First to incorporate temperature effects via electron-phonon renormalization in screening half-Heusler compounds for thermoelectric performance improvement.

Findings

Identified 3 promising half-Heusler compounds with temperature-induced band convergence.

Predicted and experimentally confirmed enhanced Seebeck coefficient at elevated temperatures.

Demonstrated the significance of temperature effects on electronic structure for thermoelectric material design.

Abstract

Enhancing band convergence is an effective way to optimize the thermoelectric (TE) properties of materials. However, the temperature-induced band renormalization is commonly ignored. By employing the recently-developed electron-phonon renormalization (EPR) method, the nature of band renormalization in half-Heusler (HH) compounds TiCoSb and NbFeSb is revealed, and the key factors for temperature-induced conduction band convergence in HH are found out. Using these as the screening criteria, 3 out of 274 HHs (TiRhBi, TiPtSn, NbPtTl) are then stood out from our MatHub-3d database. Taking TiPtSn as the example, it shows the conduction band convergence at mid-high temperature, and further resulting in enhanced Seebeck coefficient S: e.g., at 600 K with electron concentration 10^20 cm^-3, the predicted S with and without renormalized band is 352.83 uV/K and 289.52 uV/K, respectively. Herein, the former is closer to our measurement value of 338.79 uV/K. Besides, the effective masses obtained from calculation and experiment are both enlarged with temperature, indicating the existence of band convergence. Our work demonstrates for the first time the significance of adding the temperature effect on electronic structure in the design of potential high-performance TE materials.