Computational investigation of CaZnGe and CaZnSn half-heusler compounds: Potential candidates for thermoelectric devices

Using density functional theory-based computational techniques, the structural, electrical, optical, thermoelectric, mechanical, along with thermodynamic characteristics of CaZnGe and CaZnSn HH-compounds are reported in this paper. The study employs the Full-Potential Linearized Augmented Plane Wave + local orbital (FP-LAPW+lo) technique within the WIEN2k code, along with the BoltzTraP code for thermoelectric properties and the ELAST package for elastic constants. The studied materials crystallize in the F43m space group with lattice constant of 6.546 and 6.917 Å respectively, exhibiting semiconductor behavior with an indirect band gap of 1.073 eV and 0.921 eV correspondingly. Optical properties, including dielectric constant, refractive index, and absorption spectra, are thoroughly examined. Thermoelectric properties, like the Seebeck parameter and figure of merit, are analyzed, showing a dependence on doping concentration and temperature. Mechanical stability criteria, including stiffness constants, Voigt-Reuss-Hill approximation, and elastic constants, indicate mechanical stability but brittleness in ambient environments for the compounds. Thermodynamic properties, such as bulk modulus, Grüneisen parameter, and entropy, are calculated using Gibbs2 code, providing insights into the materials' thermal behavior across varying temperatures and pressures.