The influence of the X atoms and Al 3p occupied states in AlTiX2AlTiX2(X=Fe,Cu,Co,Ni)(X=Fe,Cu,Co,Ni) intermetallics

The electronic structures of the ternary (Heusler) L21L21-phase compounds AlTiX2AlTiX2(X=Fe,Cu,Co,Ni)(X=Fe,Cu,Co,Ni) are calculated by first-principles using full potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The ab initio results are analyzed with a simplified model for Al-based compounds containing transition metal (TM) atoms. The results show that the total density of state (DOS) depends strongly on the positions of TM atoms, and the TM d DOS not only connects with the pseudo-gap which is the indication of the stability of the intermetallic ternary Hume–Rothery (H–R) alloys, but also plays a crucial role in hybridization with other element valence electrons. However, the Al 3s states are repelled far away from the Fermi energy in all studied samples, and the Al 3d states are far more extended-like in the character than the d states. Furthermore, the total DOSsDOSs in all the studied samples are modulated by Al 3p states and the Al 3p states are more sensitive than d states to change in the electronic interactions. Then, the Al 3p is also responsible for the major part of the H–R stability of the intermetallic compounds which we have concerned with here. Indeed, the DOSsDOSs of the studied alloys show a pseudo-gap near the Fermi level, commonly attributed to the H–R phenomenon. Especially, the AlCu2TiAlCu2Ti has more particular flat total DOS than the other AlTiX2AlTiX2 alloys (X=Fe,Co,Ni)(X=Fe,Co,Ni), which shows the so-called half-metallic behavior or poor metallic character.