Understanding the pressure effect on the physical properties of half-Heusler semiconductor LiCaX (X = As, Sb, N) compounds from Ab-initio calculations

Abstract

The study delves into the structural, elastic, electronic, thermodynamic, and lattice dynamical and optic properties of LiCaX (X = As, Sb, N) ternary half-Heusler compounds under varying pressure and temperature conditions. Employing density functional theory with the generalized gradient approximation (GGA) in VASP codes, the initial steps involve optimizing the structure of the compound (cubic MgAgAs-type, space group F43m, C1b), determining elastic constants (C11, C12, and C44), and calculating elastic moduli (bulk modulus, shear modulus, Young's modulus). Other mechanical parameters such as Pugh's ratio, Poisson's ratio, and Zener anisotropy factor are also derived, providing insights into the brittle/ductile characteristics and isotropic/anisotropic behavior. The study further explores different vibrational modes in the compounds, and the effects of pressure on elastic anisotropy, vibrational, and optical properties are thoroughly investigated. Utilizing the quasi-harmonic Debye model, the research successfully reports V/Vo, bulk modulus, thermal expansion coefficient, and heat capacity at constant volume over a temperature range from 0 to 1000 K. The variation of photon energy is analyzed concerning the real and imaginary parts of the dielectric constant, refractive indices, extinction coefficient, reflectivity, and energy loss function up to 20 eV. The findings encapsulate the fundamental physical properties of all considered compounds, concluding with suggestions for potential future research avenues.