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

Abstract

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 (<i>F</i>4̄3<i>m</i> 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.