Lishi Ma

Phase stability, elastic anisotropy and electronic structure of cubic MAl2 (M = Mg, Ca, Sr and Ba) Laves phases from first-principles calculations

By performing first-principles calculations within the generalized gradient approximation, the phase stability, elastic constant and anisotropy, and density of states of cubic C15-type MAl2 (M = Mg, Ca, Sr and Ba) Laves phases have been investigated. Optimized equilibrium lattice parameters and formation enthalpies agree well with the available experimental data. Elastic constants C ij have been evaluated, and these C15-type MAl2 Laves phases are mechanically stable due to the meeting of C ij to the mechanical stability criteria. Polycrystalline elastic moduli have been deduced from elastic constants by Voigt–Reuss–Hill approximation. Plastic properties were characterized via values of B/G, Poissons ratio ν and Cauchy pressure (C 12-C 44). The elastic anisotropy has been considered by several anisotropy indexes (A U , A Z , A shear and A comp), anisotropy of shear modulus, and 3D surface constructions of bulk and Youngs moduli. Additionally, the sound velocity anisotropy and Debye temperature were predicted. Finally, electronic structures were carried out to reveal the underlying phase stability mechanism of these Laves phases.

Phase stability, anisotropic elastic properties and electronic structures of C15-type Laves phases ZrM2 (M = Cr, Mo and W) from first-principles calculations

Abstract Systematic investigations of phase stability and mechanical properties of C15-type ZrM2 (M = Cr, Mo and W) Laves phases were performed using first-principles calculations. The formation enthalpies of ZrM2 are in good agreement with the theoretical and experimental values. The elastic properties, including elastic constants and moduli, Poisson’s ratio and B/G, were discussed. The elastic anisotropy was also investigated via the anisotropy indexes (AU, AZ, Ashear and Acomp), the anisotropy of shear modulus and the 3D construction of bulk and Young’s moduli. The elastic anisotropy of ZrM2 is in order of ZrCr2 < ZrMo2 < ZrW2. The variations in the shear modulus and hardness show similar trends with increasing values from ZrCr2 to ZrW2. The electronic structures for these C15-type Laves phases were analysed to obtain deeper understanding of chemical bonds and phase stabilities. Finally, the sound velocities and Debye temperatures were also investigated.