Analysis of the Stabilizing Interactions and Thermodynamic Studies in Aluminum-Transition Metal Alloys (Ti, Sc, Mn, Fe) Using Solid-State Electron Density

Abstract

The solid-state structures of Aluminum-Transition Metal (Al3TM) Alloys (TM = Ti, Sc, Mn, Fe), have been explored in detail using computational electron density methods. Topological analysis of the electron density in Al3Ti alloys revealed two interesting types of interactions between the atoms in the layered Al3Ti alloy structure lattice; viz. Al-Al and Al-Ti interactions. Two types of both Al-Al interactions and Al-Ti interactions were observed between the atoms in the same plane (2.725 A apart), and those on adjacent planes or layers (2.884 A apart). All interactions in the same plane of the Al3Ti alloy are stronger than those on adjacent planes, owing to the high values of the electron density and the bond distances between the interacting atoms (Table 1). The Laplacian of the electron density in a plane of the alloy indicates that Ti atoms are polarized towards the Al-atoms thereby transferring most of their valence electron density to Al (Figure 2b). Similar interactions were observed in Al3Sc alloy but these interactions were weaker than those in Al3Ti alloy. This signifies that Ti and Al atoms in the alloy are interchangeable or completely miscible, and indicates an increased stability of the alloy compared to Al3Sc alloy. In addition, analysis of Al3Mn and Al3Fe alloys indicate that these alloys were more stable compared to Al3Ti and Al3Sc alloys. Furthermore, the thermodynamic studies of Al3TM alloys (TM = Ti, Sc, Mn, Fe) were investigated. The results confirm the conclusion that Al3Ti and other Al-based transition metal alloys play little or no active role in the reversible re/dehydrogenation of Ti-doped NaAlH4. These alloys are thermodynamically stable.