Etude des propriétés des matériaux dioxydes

Abstract

The structural properties, elastic constants, electronic structures and optical properties of CeO2 and ThO2 were studied by the DFT within the GGA. The calculated equilibrium lattice constants and bulk moduli for the two compounds were compared with those obtained with other theoretical methods and with experimental data when available. The calculated pressures at which these compounds undergo a structural phase transition from fluorite to cotunnite phase are close to the experimental results, the pressure induced structural phase transition occurs at 28.9 GPa for CeO2 and 29.8 GPa for ThO2. The calculated elastic constants indicated that the two phases of CeO2 and ThO2 are mechanically stable in the studied pressure range. Moreover, the dependence of the band gap on the applied pressure is first obtained. Results show that when cubic structure transforms into orthorhombic structure under pressure, the Eg value is reduced. The optical properties of CeO2 and ThO2 compounds with the physical quantities, such as the complex dielectric function have been presented in this work.