Electronic, phonon and thermoelectric properties of RbLaGe half-Heusler alloy: A DFT study including spin-orbit coupling

The phonon, electronic and structural properties of the novel RbLaGe half-Heusler alloy are analysed using density functional theory (DFT) with the generalized gradient approximation (GGA). The semiclassical Boltzmann transport theory under the constant relaxation time approximation is employed specifically to evaluate the thermoelectric properties. The results reveal that RbLaGe is energetically, structurally, and dynamically stable, suggesting its potential for experimental synthesis. RbLaGe exhibits semiconducting behaviour with a direct bandgap, 0.79 eV. Spin-orbit coupling has a more pronounced effect on the conduction band other than on the valence band, leading to a splitting of 0.01 eV approximately at point X. Thermoelectric properties, including power factor (P F/τ ), merit figure (ZT), electronic thermal conductivity (κe/τ), electrical conductivity (σ/τ ) and Seebeck coefficient, are analyzed using Boltzmann transport theory within the rigid band approximation. The results propose that RbLaGe exhibits high thermopower, which is attributed to the flat band near the Fermi level. Furthermore, the power factor (P F) shows a strong temperature dependence, reaching a maximum value,9.9 × 10¹¹ W/mK²s at 900 K. The calculated thermal conductivity of the lattice (κL) reveals a significant temperature-dependent reduction, improving the merit thermoelectric figure (ZT). Incorporating spin-orbit coupling (SOC) further improves ZT by optimizing the electronic transport properties.