First-principles study of polymorphism in Ta4AlC3

The electronic structure and phase stability of Ta4AlC3 with αα and ββ polymorphs are studied by first-principles calculations. The calculated formation energies are −0.649 and −0.576 eV/atom for the αα and ββ polymorphs respectively, which means that both of them are thermodynamically stable phases. The total energy of αα- Ta4AlC3 is about 0.0866 Ry lower than that of ββ- Ta4AlC3, indicating that the αα polymorph is more stable. The strong hybridization between Ta1 5d and C1 2p, Ta2 5d and Al 3p in αα- Ta4AlC3 results in strong interactions between Ta1–C1 and Ta2–Al atoms, which stabilizes the αα polymorph of Ta4AlC3.