Etude des propriétés structurales, élastiques et électroniques des composés antiperovskites de type XNCa3.

Abstract

This manuscript presents a theoretical study, within the density functional theory framework (DFT) and the pseudopotentials with planes waves approach, of the structural, elastic, electronic and thermodynamic properties for the antipérovskites compounds XIVNCa3 with XIV ≡ Ge, Sn et Pb et XVNCa3 with XV ≡ P, As, Sb et Bi. The structural, elastic and electronic properties have been calculated within the two approximations for exchange correlation energy: local density approximation of Ceperley and Alder parameterized by Perdew and Zunger (LDA-PZ) and the generalized gradient approximation of Perdew-Burke Ernzerhof (GGA-PBE), 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 equilibrium geometries of the studied materials have been optimized at 0 K for different pressure values between 0 and 40 GPa by using the CASTEP package. The study of the electronic structure and the chemical bonding properties of the considered compounds, under pressure effect, have been performed through the calculation of the band structure, total and partial electronic density of states diagrams (TDOS and PDOS) and the valence electronic charge distribution maps. For a good description of the mechanical behavior of the studied compounds, we have first calculated theirs single-elastic constants Cij. The obtained numerical values of Cij have been then used to estimate the elastic anisotropy, verify the mechanical stability of the antipérovskite structure, and also to calculate the sound waves velocities in the principles directions. Based on the Voigt-Reuss-Hill method values, we have investigated the elastic properties of the considered material in polycristallin state by using the calculated anisotropic elastic constants Cij : the isotropic elastic moduli including bulk modulus B, shear modulus G, Young modulus E and Poisson’s ratio ƞ have been calculated. The elastic properties have been completed by calculating the isotropic acoustic waves velocities and Debye temperature. In order to investigate the thermodynamic properties of XIVNCa3 and XVNCa3 antiperovskites 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 as function of temperature for different pressure values.