Structural, elastic, thermodynamic, electronic, and optical properties of CaMg2AN3(A=Al and Ga): ab initio investigation

The present paper aims to investigate the structural, elastic, thermodynamic, electronic, and optical properties of CaMg 2 AN 3 ( A = Al and Ga) using first-principle calculations and quasi-harmonic Debye model. The obtained ground-state lattice parameters were in good agreement with the experimental values. Pressure effect on the structural parameters was tested up to 20 GPa, the results reveal that the contractions are higher along the c-axis than along the a-axis. The computed single-crystal elastic moduli show that the unidirectional constant C 11 is about 60% greater than C 33 . Cauchy pressure and Poisson ratio suggest that the chemical bonding in CaMg 2 AN 3 is a mixture of covalent and ionic characters. Elastic anisotropy was discussed using different approaches, and the results show a weak elastic anisotropy. By means of Gibbs program, we have evaluated the thermodynamic properties such as Debye temperature θ D , heat capacities C v and C p , and expansion thermal coefficient under pressure ranging from 0 to 20 GPa and at temperature ranging from 0 to 1500 K for both compounds. The evaluated value of Dulong–Petit limit of both the semiconductors is 360.5 Jmol - 1 K - 1 . Band structure curves show a direct band gap of about 1.88 and 0.78 eV for CaMg 2 AlN 3 and CaMg 2 GaN 3 , respectively. Density of states and charge densities analysis confirm the predicted ionic-covalent bonding in both nitrides. Additionally, optical functions such as the refractive index, the reflectivity, and the absorption coefficient were calculated and discussed for two polarized radiations. Graphic abstract