First-principles investigation of LiSnAl and LiSiIn half-Heusler compounds for optoelectronic applications

This study presents a comprehensive first-principles investigation into the structural, electrical, magnetic, mechanical, optical, and thermodynamic properties of two lithium-based half-Heusler semiconductors, LiSiIn and LiSnAl. Our findings confirm that both LiSiIn and LiSnAl possess a cubic C1b crystal structure (F4̄3m space group) and satisfy Born's stability criteria, confirming their mechanical stability. They exhibit indirect and narrow band gaps of 0.095 eV (LiSnAl) and 0.228 eV (LiSiIn) with GGA-PBE, and 0.517 eV (LiSnAl) and 0.591 eV (LiSiIn) with HSE06, indicating semiconducting behavior Charge density and Mulliken population analyses reveal a mixed ionic-covalent bonding, while negative Cauchy pressure indicate brittleness. LiSiIn demonstrates superior stiffness, deformation resistance, and fracture strength compared to LiSnAl. Optically, both compounds exhibit high dielectric constants, UV reflectivity (56-60%), and strong low-energy absorption, suggesting potential applications in capacitors, photovoltaics, and thermophotovoltaics. Phonon dispersion confirms dynamic stability, and thermodynamic results show low minimum thermal conductivities (∼0.006-0.007 W m^-1 K^-1) and high melting points (1003.46 K for LiSnAl, 1100.02 K for LiSiIn). The higher melting point of LiSiIn reflects stronger bonding, while LiSnAl's lower thermal conductivity favors thermal energy storage. Overall, both materials demonstrate multifunctional potential for next-generation energy and optoelectronic devices.