Prédiction à partir des différentes phases cristallines des propriétés physiques et mécaniques des céramiques dentaires

Abstract

We have used the pseudo-potential and plan wave method (PP-PW) based on density functional theory (DFT) to examine the physical and mechanical properties of dental ceramics systems based on the crystals Li2Si2O5, Ca5(PO4)3F and MgAl2O4, by calculating the structural properties, phase stability, elastic properties, electronic and optical properties of these crystals (phases). The various properties were calculated in the framework of the local density approximation (LDA) and the generalized gradient approximation (GGA) using CASTEP code. The calculated structural properties such as the equilibrium lattice parameters, cell volume and the bulk modulus are generally in good agreement with the available experiment and theoretical results. The structural stability of the different phases was evaluated by calculating their formation enthalpies. The obtained results show that these phases are energetically more stable, thus suggesting the thermodynamic stability of the studied materials. Our study of elastic properties indicates also that these phases are mechanically stable in the normal conditions. Our values of the polycrystalline elastic moduli are relatively close to the experimental values, thus indicating the reliability and the predictive power of the applied method. We have found from these values and the hardness values that the lithium disilicate phase (Li2Si2O5) exhibits a higher stiffness than that fluorapatite (Ca5(PO4)3F), but it is less hard than the spinel phase (MgAl2O4). To further elucidate the insulating nature of the different dental systems, we have calculated the band structure and density of states (DOS) of Li2Si2O5, Ca5(PO4)3F and MgAl2O4 compounds. The calculations indicate that these phases have an insulator character. Optical parameters such as refractive index, extinction coefficient, absorption coefficient and optical reflectivity have been determined from the calculations of the complex dielectric function of these compounds. The results obtained allowed as to provide an insight into the optical behavior of the studied materials.