Analyzing the physical properties of Half-Heusler RNiSb (R = Sc, Y) for optoelectronic and thermoelectric applications based on first-principles theories

Abstract In this study, we investigated the RNiSb (R = Sc, Y) half-Heusler material for various properties including structural, electronic, mechanical, elastic anisotropic, optical, and thermal properties using Density Functional Theory (DFT) with the Cambridge Serial Total Energy Package (CASTEP) code. Our analysis of the lattice parameters closely aligns with previous theoretical and experimental findings. The positive phonon dispersion curve confirms the dynamical stability of RNiSb (R = Sc, Y). The elastic constants meet the Born criteria, indicating the mechanical stability and brittleness of the RNiSb (R = Sc, Y) solids. While ScNiSb displays elastic isotropy, YNiSb exhibits elastic anisotropy. Electronic band structure and Density of states (DOS) calculations reveal that ScNiSb and YNiSb have indirect band gaps of 0.44 eV and 0.589 eV, respectively. We also determined key optical properties such as absorption coefficient, dielectric function, conductivity, reflectivity, refractive index, and loss function. The optical properties calculations revealed strong photoconductivity, and high reflectivity, all of which show given the materials use in the microelectronics, and optoelectronics application. Furthermore, the Debye temperature and minimum thermal conductivity of ScNiSb decrease with the replacement of Sc by Y, highlighting its potential as a material for thermal barrier coating (TBC). Finally, we computed the Helmholtz free energy ( F ), internal energy ( E ), entropy ( S ), and specific heat capacity ( C v ) based on the phonon density of states.