Ab initio calculation of the formation energies of L12, D022, D023 and one dimensional long period structures in TiAl3 compound

The relative stabilities of L12, D022, D023 and several one dimensional long period structures (1D-LPSʹs) in the TiAl3 intermetallic compound are investigated employing the Vienna ab initio simulation package (VASP). The energetic effects due to the tetragonal distortion of the D022, D023 structures and other 1D-LPSʹs are important. The effect of the cell-internal displacements of the atoms in the long period structures has also been studied. After this last stage of relaxation D023 is found to be the ground state. With distortion only, D022 is the most stable structure. 1D-LPSʹs with one and two bands have energies which are very near to those of D023 and D022. The formation energies of TiAl3 in the L12, D022, and D023, structures are calculated. The computed electronic densities of states show that each structure has a pseudo gap in its density of states distribution. The energetic results are discussed in the framework of the axial nearest neighbor Ising model (ANNNI). Predictions of the energy differences from L12 of series of 1D-LPSʹs are provided.