A comprehensive DFT study on the physical attributes of Li based Half-Heusler compounds LiYXZ (X = Pt, Pd; Z = Si, Ge)

In the present article, we have explored two quaternary Heusler compounds LiYXZ (X = Pt, Pd; Z = Si, Ge) possessing 18-valence electrons. The electronic band plots of both compounds reveal the semiconducting nature of them depicting the presence of an indirect forbidden energy gap of 1.038 eV for LiYPtSi and 0.443 eV for LiYPdGe respectively. This report presented the structural stability, mechanical, electronic, optical and transport properties were investigated by the FP-LAPW method and semiclassical Boltzmann transport theory using first-principles calculations for the practical utilization of the materials. Exchange-correlation effect is treated with the generalized gradient approximation with Perdew Burke Ernzerhof scheme (GGA-PBE) and Trans-Blaha modified Becke-Johnson (mBJ) exchange potential. Important optical responses of studied quaternary Heuslers are found in the visible and infrared energy range. The melting point of LiYPtSi and LiYPdGe are calculated as 1353.59 ± 300 K and 1435.20 ± 300 K respectively; owing to this fact all the prime thermoelectric properties along with the Figure of Merit (zT) are calculated in the temperature range of 1200 K. The investigated materials are purely anisotropic with ductile property, dynamically and mechanically stable. In an overview of thermoelectric properties, the Seebeck coefficient and the lattice thermal conductivity at 300 K for LiYPtSi are 241 μV/K, 1.34 × 10¹⁵ W/mK and for LiYPdGe are 238 μV/K, 1.00 × 10¹⁵W/mK respectively. The respective value of zT was 0.06 and 0.068 at the 300 K that ensures the materials is not to be efficient thermoelectric elements in the room-temperature range but at high temperature.