Structural stability, elasticity, thermodynamics, and electronic structures of L12-type Ni3X (X = Al, Ti, V, Nb) phases under external pressure condition.

In this paper, the effect of pressure on the structural stability, elasticity, thermodynamics, and associated electronic structure of L12-type Ni3X (X = Al, Ti, V, Nb) phases is investigated using a first-principles approach. It is shown that pressure leads to volume compression of the Ni3X phase and reduction of the lattice parameters. The increase of pressure promotes the increase of elastic constants, bulk modulus, shear modulus, and Young's modulus. And there is an extremely strong linear correlation between the pressure and the elastic constants. The calculated elastic constants indicate that the pressure leads to strong mechanical stability and ductility of the Ni3X phase. Mechanical anisotropy of the Ni3X phase also increases with increasing pressure. The electronic analysis shows that the increase in pressure leads to enhanced Ni-d-orbitals and X-d-orbitals hybridization and increased electron transfer. The order in terms of electron accumulation intensity is Ni3Ti > Ni3Nb > Ni3V > Ni3Al. It is more directly reflected in the charge density difference diagram. This is in agreement with the results of the enthalpy of formation (ΔH) and Debye temperature (ΘD) analysis.