Étude des propriétés structurales, électroniques élastiques optiques et thermodynamiques de quelques matériaux ternaires

Abstract

Our work deal with the study of hydrostatic pressure effect on the structural, elastic, electronic optical and thermodynamic properties of ternary compounds: Ca4XN4 with X≡ Ti, Si and Ge. The study is based on the first-principle (ab-initio) calculation by using the density functional theory ﴾ DFT﴿ within the pseudopotential method, by using the CASTEP package. The thermodynamic properties have been investigated by using the GIBBS program which is based on the quasi-harmonic model of Debye. The calculated lattice constants are in good agreement with the experimental measurements. The study of the electronic structure and the chemical bonding properties of the considered compounds, have been performed through the calculation of the band structure, total and partial electronic density of states diagrams (TDOS and PDOS). The electronic band structure calculations suggest that these compounds are insulators. Single crystal elastic stiffness’s (Cij) were calculated and the polycrystalline elastic moduli (B and G) were estimated according to Voigt, Reuss and Hill's approximations. The variation of various optical parameters such as: the dielectric function, the optical absorption, the refractive index, the extinction coefficient, the optical loss function and the reflectivity at 0GPa and under pressure, for our compounds, have been studied. In order to investigate the thermodynamic properties of Ca4XN4 under pressure and temperature effect, we have calculated the variation of the lattice parameters, bulk modulus and thermal expansion coefficient, heat capacity at constant volume CV, heat capacity at constant pressure CP and Debye temperature