First-Principles Investigation of Structural Stability, Mechanical, Electronic, and Thermoelectric Properties of LiYN (Y = Sr, Mg, Zn) Compounds Under Hydrostatic Pressure

Abstract

This study investigates the pressure-dependent structural, electronic, mechanical, and thermoelectric properties of LiYN (Y = Sr, Mg, Zn) half-Heusler compounds using first-principles calculations. The structural stability was analyzed by fitting the total energy versus volume curves using the Birch–Murnaghan equation of state, allowing the determination of equilibrium lattice parameters and bulk moduli at pressures of 0, 5, and 10 GPa. Elastic constants were calculated to assess the mechanical stability, and all compounds satisfy the Born stability criteria over the entire pressure range. The Pugh ratio (B/G) and Poisson’s ratio (ν) indicate that LiSrN, LiMgN, and LiZnN exhibit predominantly brittle behavior under 0 GPa. Electronic band structure calculations reveal that LiMgN and LiZnN exhibit direct band gaps, whereas LiSrN shows an indirect band gap. Increasing pressure leads to a systematic widening of the band gaps due to lattice compression. Thermoelectric properties were evaluated using the Boltzmann transport theory within the constant relaxation time approximation. The Seebeck coefficient, electrical conductivity, and figure of merit (ZT) were found to be strongly dependent on both temperature and pressure. Notably, at 300 K, the ZT values increase from 0.005, 0.35, and 0.54 at 0 GPa to 0.027, 1.12, and 1.13 at 10 GPa for LiMgN, LiSrN, and LiZnN, respectively. These results demonstrate that hydrostatic pressure significantly enhances the thermoelectric performance of LiYN compounds, highlighting their promising potential for thermoelectric energy conversion applications.