Strain-dependent electronic and dynamical properties of ZrIrBi half-Heusler: A fundamental understanding based on ab initio principles

Enhancing the thermoelectric (TE) performance of materials requires the material’s structural stability over a wide range of temperatures. This research demonstrates a concurrent enhancement in lattice dynamical stability and the impact of isotropic tensile and compressive strains on ZrIrBi, a thermoelectric material, as determined by ab initio calculations. By use of ab initio molecular dynamics (AIMD), a supercell is generated from a conventional unit cell, and the Brillouin zone is sampled with a k-point mesh. The AIMD calculations are performed at temperatures of 300 K and 900 K. Our study examines electronic structure, mechanical properties, lattice dynamics, Seebeck coefficient, electrical and thermal conductivity, power factor (PF), and the figure of merit (ZT). The results indicate unique strain-dependent traits in the electronic properties of ZrIrBi, including a fictitious band convergence effect, as identified through first-principles calculations incorporating GW self-interaction correction. The study demonstrates that tensile strain efficiently tunes the band gap, substantially modifying the electronic structure and enhancing the power factor (PF). Concurrently, tensile strain alters lattice dynamics substantially, decreasing the lattice thermal conductivity (k_l). The combined effects lead to a fourfold enhancement of ZT at elevated temperatures. The study presents a detailed approach for exploiting isotropic strain to realize high-efficiency thermoelectric materials, informing the experimental investigation of materials with enhanced ZT.

KEY WORDS: Half-Heusler, electronic structure, thermoelectric efficiency, isotropic strain, tensile strain, strain-dependent