Exploration of some physical properties of new half-Heusler compounds BiXSr (X = Li and K) using first-principles calculations

Abstract

Good thermoelectric (TE) materials with high energy conversion efficiency are required to improve energy utilization and help meet increasing energy demands. By combining first-principles calculations with the Boltzmann transport theory, this study systematically investigates the electronic structure, mechanical properties, and TE performance of the half-Heusler compounds BiLiSr and BiKSr for the first time. Phonon spectrum calculations indicate that BiXSr (X = Li and K) exhibits dynamic stability. The calculated elastic constants demonstrate that BiXSr (X = Li and K) is mechanically stable and ductile. Electronic structure analysis reveals that BiLiSr is a direct-bandgap semiconductor, whereas BiKSr is an indirect-bandgap semiconductor. The TE performance results for BiXSr (X = Li and K) show that the Seebeck coefficient is superior under p-type doping, whereas the power factor is higher under n-type doping. Under n-type doping conditions, the maximum power factor values for BiLiSr and BiKSr are 852.14 and 572.85 µW m⁻¹ K⁻², respectively. At 300 K, the lattice thermal conductivity of BiKSr is consistent with previous theoretical studies. At 900 K, the calculated electronic TE figure of merit (ZT_e) for both BiLiSr and BiKSr is 0.99. Considering the dynamic stability, mechanical stability, and TE performance of BiXSr (X = Li and K), this series of compounds demonstrate potential as promising TE materials over a wide temperature range.