Calcul ab initio des enthalpies de formation des composés ZrAl3 et HfAl3

The relative stabilities of L1 2 , D0 22 , and D0 23 structures in ZrAl 3 and HfAl 3 compounds are investigated employing the Vienna ab initio simulation package (VASP). In ZrAl 3 and HfAl 3 compounds, the energetic effects related to the tetragonal distortion are important and lead to the stabilization of the D0 22 and D0 23 structures with respect to the L1 2 structure. The effect of the cell internal displacements of the atoms in the D0 23 structure is studied. In the case of the HfAl 3 compound, the D0 23 structure appears as the most stable structure after this last stage of relaxations. In the case of ZrAl 3 compounds, the D0 23 structure is the most stable structure in both distorted and fully relaxed stages of the relaxation. The results are discussed in the framwork of an antiphase boundary model.