General trends in the structural, electronic and elastic properties of the M3AlC2 phases (M = transition metal): A first-principle study

In this paper, the first-principles pseudopotential total energy method is used to predict the structural, electronic and elastic properties of the M3AlC2 (MAX) phases, where M = 3d, 4d, and 5d early transition metals. Specifically, the effects of the valence electron concentrations (VEC) of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W were examined. The lattice constants are a linear function of the atomic diameter of the M element. In general, M d–Al p hybridizations locate just below the Fermi level and are weaker than the M d–C p bonds, which are deeper in energy. The bulk moduli of the ternary carbides are found to be proportional to the bulk moduli of the corresponding binary carbides. Because the M–Al bonds are less stiff than the M–C bonds, the latter are mainly responsible for the high bulk moduli of the M3AlC2 phases. The M–Al bonds, on the other hand, play a critical role in decreasing the bulk moduli compared to the binary carbides.