Etude du premier principe des propriétés électroniques, optiques et mécaniques des matériaux hôtes.

Abstract

We investigate the electronic, thermodynamic and bonding properties of the ThGeO4 host material by means of pseudo-potential method within the framework of density functional theory. Zircon-type ThGeO4 is found to undergo a pressure-driven phase transition to tetragonal scheelite structure, and beyond to monoclinic fergusonite ones. Emphasis is placed on the trends of the dynamical stability and anisotropic behavior related to structural phase transition. Linear as well as cubic thermal expansion component show a different directional dependence as a function of temperature for the investigated polymorphs of the compound. The origin of the difference in the unit cell expansion is found to be related to the distortion of the ThO8 dodecahedra. The analysis of the non-covalent dispersion of the zircon and scheelite structures reveals a counter-balance between destabilizing interactions due to steric crowding and the current attractive and repulsive ones.