Résumé
First principles calculations are done for Mg2X (X = Si, Ge or Sn) antifluorite compounds and their solid solution in order to investigate their pseudo-binary phase diagram. We find formation energies that agree qualitatively with experiment for the parent compounds. For X = Si and Ge, there is complete solubility, but there is a miscibility gap in the pseudo-binary phase diagram Mg2Si-Mg2Sn. These results agrees with the most recent experiments and phase diagram assessment for these pseudo-binary phase diagrams. We also find that the energy bandgap strongly decreases when Si is substituted by Sn, in agreement with the experiment. Supercell calculations are also done for determining the most stable defects and the doping indued by thse defects in the three parent compounds. From this study, we deduced that the intrinsic p-doping in pure Mg2Si can be attributed to the presence of magnesium atoms in interstitial position. Coversely, in Mg2Ge and Mg2Sn, there are other stable defects and this explains why they can also be n-type.