First-principles phase stability and elastic properties of Al-La binary system intermetallic compounds

The phase stability and the elastic properties of Al-La binary system intermetallic compounds were thoroughly investigated using first-principles calculations. Firstly, the 0 K phase diagram for this system was calculated using the formation enthalpy convex hull construction, which indicates three metastable phases, namely Al4La (I4/mmm), Al4La (Imm2), and AlLa3 (Pm-3m). Then, the stability of Al11La3 was examined at temperatures lower than 1000 K compared with the two Al4La allotropes and the Al + Al2La two-phase equilibrium. The results demonstrate that the needlelike phase in Mg-Al-La based alloys should be indexed as Al11La3, which is thermodynamically stable, with no decomposition under aging. Thirdly, AlLa3 (Pm-3m) is more stable than AlLa3 (P63/mmc) at temperatures higher than approximately 590 K, which well agrees with the experimental results. Finally, the elastic properties and vibrational properties for the stable Al-La intermetallic phases were calculated in this work.