Cohesive, electronic, and structural properties of Al3Li: An important metastable phase

The cohesive and electronic properties and the structural stability of Al3Li in its fcc-based L12 and bcc-based D03 structures are investigated with use of the first-principles all-electron full-potential linear augmented-plane-wave (FLAPW) method. Particular care was taken to ensure convergence of the total energy as a function of the inherent numerical parameters in order to obtain high precision. To further understand the calculated stability, the electronic structure of some superstructures (notably Al7Li and Al5Li3) was also determined. The equilibrium properties of the metastable L12 structure are in good agreement with experiment. A simple picture emerged which emphasizes the importance of the anisotropic bonding between the Al atoms with the Li basically donating its valence electron to strengthen the Al bonds. The bulk moduli were found to decrease with increasing Li content; by contrast, the calculated Youngs modulus of the L12 phase is high (1.20 Mbar) compared to the bulk modulus (0.72 Mbar). Both results are in keeping with the picture of anisotropic Al-Al bonding.