Phase stability, structural and elastic properties of C15-type Laves transition-metal compounds MCo2 from first-principles calculations

• HfCo2 has the highest phase stability.
• All the C15-type Laves phases MCo2 are mechanically stable.
• The degree of elastic anisotropy is ordered as: ScCo2 < TiCo2 < YCo2 < NbCo2 < TaCo2 < ZrCo2 < HfCo2.

First-principles method is performed to systematically investigates structural, phase stability and mechanical properties for the Laves phases MCo2 (M = Sc, Ti, Y, Zr, Nb, Hf, Ta) with C15-type structure. The calculated equilibrium structures and formation enthalpies are very close to the available experimental and HfCo2 has the highest phase stability. The elastic properties, including elastic constants, Poisson’s ratio and anisotropy index are also calculated. Shear modulus and hardness of MCo2 have the same variation tendency; the degree of the elastic anisotropy for MCo2 is in the order: ScCo2 < TiCo2 < YCo2 < NbCo2 < TaCo2 < ZrCo2 < HfCo2. Finally, Debye temperatures and sound velocities are also investigated.

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