Strain trailing band engineering and phonon transport of high ZT ZrCoBi half-Heusler alloy: a mechanistic understanding from first principles

Abstract

Enhancing the thermoelectric (TE) performance of materials requires simultaneous optimization of the power factor (PF) and reduction of thermal conductivity (κ), a challenging task due to their interdependent nature. This work demonstrates a concurrent enhancement of PF and reduction of κ in p-type half-Heusler compound, ZrCoBi. Using ab initio electronic structure calculations, we investigate the impact of isotropic tensile and compressive strains on the TE properties of materials. Our analysis encompasses electronic structure, mechanical properties, lattice dynamics, Seebeck coefficient, electrical and thermal conductivity, PF, and the figure of merit (ZT). The results reveal a unique strain-dependent behavior in the electronic properties of ZrCoBi, including a spurious band convergence effect, as identified through first-principles calculations incorporating spin–orbit coupling (SOC). Furthermore, the analysis shows that tensile strain effectively tunes the band gap, significantly altering the electronic structure and improving PF. At the same time, tensile strain induces significant changes in lattice dynamics, reducing lattice thermal conductivity (κ_L). These combined effects result in a fourfold increase in ZT at high temperatures. This study also provides a comprehensive framework for leveraging isotropic strain to achieve high-performance thermoelectric materials and guides the experimental exploration of enhanced ZT compounds.